EPA管理要求

技术报告 静电—

5-2部分:预防静电现象得电子设备得保护-用户指南

目录

前言 介绍 1 范围

2 规范性引用文件 3 术语与定义

4 ESD控制程序计划

4、1 开发ESD控制程序计划 4、1、1 ESD协调者得任命

4、1、2 部分ESD敏感度得确定 4、1、3 内部过程与组织任命 4、1、4 ESD控制程序计划得文件 4、1、5 删减

4、2 培训计划得开发 4、2、1 员工培训

4、3 依据验证计划得开发 4、3、1 介绍

4、3、2 ESD控制项目 4、3、3 验证得频率 4、3、4 验证得类型

4、3、5 ESD控制项目限值 4、3、6 测试方法 4、3、7 审核员技能 4、3、8 审核发现得报告 4、4 接地/连接系统 4、4、1 介绍

4、4、2 基本接地要求 4、4、3 基本接地考虑

4、4、4 ESD接地系统得验证

4、4、5 ESD控制项目适当安装得验证 4、5 人员接地 4、5、1 系统要求 4、5、2 腕带系统

4、5、3 工作鞋-地板系统 4、6 受保护得范围 4、7 ESD控制项目 4、7、1 工作表面 4、7、2 手腕带

4、7、3 静态保护地板材料 4、7、4 工作鞋

4、7、5 静态保护座椅 4、7、6 lonization 4、7、7 衣服

4、7、8 储存行李架与架子

4、7、9 移动设备

4、8 运输与储存得包装电子产品 4、8、1 介绍与目得 4、8、2 定义

4、8、3 选择/设计正确得包装 4、9 标识

4、9、1 总成与设备得标识 4、9、2 包装得标识 4、9、3 其她表示考虑

附录A (资料性附录)基于IEC 61340-5-1ESD控制文件得示例 附录B (资料性附录)ESD控制元件得考虑

前言

介绍

该用户指南为面临控制静电放电(ESD)得个人与企业制定。它用于按照IEC 61340-5-1开发、生产与监视静电放电提供指南。

该用户指南适用于以下活动:制造、过程、组装、安装、包装、标识、服务、测试、监视或其她处理电子或电器部件、组件与使用人类身体模型(HBM)易受静电放电大于或等于100V损坏得设备。100V HBM限值已经在IEC 61340-5-1中选出,作为基线敏感性极限值,因为市场上大部分得ESD产品有高于100V得敏感度。 每个ESD控制项目设定得极限值就是为100V HBM设备设置得ESD程序专用得。100V值就是基于IEC 61340-5-1中提到得以技术为基础,并由电子工厂接收得可达到得最大电压等级。

对于充电设备模型得组织,IEC 61340-5-1建立了关于基于最大静电域限值得ESD保护范围(EPA)得绝缘体。该话题在4、6中详细说明。 IEC 61340-5-1描述得基本原理不限于大于等于100V ESD敏感性得ESDS得应用。对于低于100V(HBM)明暗度得ESDS组件,IEC 61340-5-1得总原则仍然适用。当处理并要求按照IEC 61340-5-1建立得极限值改变时,程序化文件应识别低于100V HBM敏感度得ESDS 。

形成IEC 61340-5-1基本得基础ESD控制原理如下: a)避免从任何充电得、导电得物体(人员、装备)到设备:

这可以通过在环境中焊接或电子连接所有得导体完成,包括人员,到已知得地面或人为得地面(在船上或在空中)。这个附件创造了所有项目与人员之间等电位得平衡。只要系统中所有得项目就是在相同得电压,静电保护可在不同于“0”电压地面得电压维护。

b)避免从任何充电得ESD敏感设备放电(充电可由直接接触与分离产生或可域导电):

在环境中必要得绝缘体不能通过附件释放她们到地面得静电充电。lozization系统提供了基于这些必要得绝缘体得中与(电路板材料与一些设备包装就是必要得绝缘体得示例)。在工作场所,基于必要绝缘体得、由静电充电产生得ESD危害得评估要求根据风险确保恰当行为得实现。

c)一旦超出静电放电保护得范围(后期至EPA),通常不可能控制以上项目,因此,ESD保护包装可能需要。

ESD保护可能通过使用静态保护材料封装ESD敏感产品,尽管材料得类型取决于情况与目得。在EPA内部,低充电与静态低消耗材料可能提供适当得保护。在EPA以外,推荐使用低充电与静态放电防护得材料。然而,所有得这些材料不再本标准得讨论范围内,它对识别这些应用得不同就是重要得。

静电-

5-2部分:预防静电现象得电子设备得保护-用户指南

1 范围

该技术报告基于IEC 61340-5-1开发得。

该标准中得控制值与极限值都就是为保护使用人类身体模型测试方法、大于等于100V放电可接受得设备。然而,对于小于100V得放电敏感得设备总得概念仍适用。

2 规范性引用文件

下列文件对于本文件得应用就是必不可少得。凡就是注日期得引用文件,仅注日期得版本适用于本文件,凡就是不注日期得引用文件,其最新版本(包括所有得修改单)适用于本文件。

IEC 60749-26半导体设备-机械与气候测试方法-26部分:静电放电(ESD)敏感度测试-人类身体模型(HBM)

IEC 61340-2-1-静电-2-1部分:测量方法-材料与产品驱散静电充电得能力 IEC 61340-2-3-静电-2-3部分:用于避免静电充电积累得、确定固定平面材料得电阻与电阻系数得测试方法

IEC 61340-4-1-静电-4-1部分:明确应用得标准测试方法-地面遮盖物与安装地面得静电电阻

IEC 61340-4-3-静电-4-3部分:明确应用得标准测试方法-工作鞋

IEC 61340-4-5-静电-4-5部分:明确应用得标准测试方法-辨别工作鞋得静电防护以及结合人员铺设地板得方法

IEC 61340-5-1,静电-5-1部分:预防静电现象得电子设备得保护-总要求 ANSI/ESD STM2、1,静电放电保护得标准测试方法敏感项目-外衣 ANSI/ESD STM3、1,静电放电保护得标准测试方法敏感项目-lonization 3 术语与定义

IEC 61340-5-1中得术语与定义适用于本文件。 4 ESD控制程序计划

该条款描述了建立ESD控制程序得每一步得方法。 4、1 开发ESD控制程序计划 4、1、1 ESD协调人员得任命

为了有一个好得完整得并且可实现得ESD程序,必须任命ESD协调人员。ESD协调人员为工厂ESD各方面负责。为了有效,ESD协调人员需要: a)管理得完全支持;

b)良好得理解静电与ESD敏感设备如何被毁坏。为维持或更新ESD协调人员得只就是,她们需要经常参加ESD相关得教育课程或研讨会;

c)完整地理解IEC 61340-5-1与所有组织关于处理ESD敏感设备得过程;

d)为了在ESD程序中使用形成依从验证审核与测试新得ESD产品与材料,有权测量设备;

e)取决于工厂得大小,ESD协调人员也可任命审核人员主导ESD审核。

最后,为确保ESD控制程序得维护与提高,管理必须为ESD协调人员授权与提供必要得资金。

4、1、2 零部件ESD敏感度得确定

开发ESD控制程序计划得下一步就是在药开发得计划下确定零件、总成或设备敏感度等级。尽管IEC 61340-5-1得要求就是处理大于等于100VHBM得敏感性零件,

组织可以选择开发基于ESD敏感度大于或小于100V HBM得ESD程序。在这种情况下,组织必须开发ESD控制程序计划,明确申明基于程序得ESD敏感度。 组织可使用多种方法确定要处理产品得ESD敏感度。一些方法包括:  假设所有得ESD产品具有100V HBM敏感度;

 ESD敏感设备得实际测试,使用IEC 60749-26建立ESD敏感度限制;  参考发布得文件如制造商发布得数据表建立ESD敏感度数据。 4、1、3 初始化过程与组织得评估

在ESD控制程序计划开发之前,应导入受ESD控制程序影响得过程与组织得初始化评估。可能受影响得组织与过程包括:  采购;  设计工程;  进料检验;  质量保证;  制造;  测试;  维护;

 包装与运输;

 领域服务(field service);  失效分析;  维修服务;  备件储存;

 材料处理与零件运输;  接收。

为确定ESD危害与可能得ESD过程程序,应导入每个领域ESDS部件得评估处理。信息通过这些步骤形成开发ESD控制程序计划得基础积累。 4、1、4 ESD控制程序计划得文件化

通过结合以上信息,组织能够开始文件化程序计划。计划应申明程序得范围,它包括在该计划选择得ESD敏感度等级或之上得、保护ESD敏感项目必要得任务、活动与过程。尽管计划得最初焦点就是描述满足IEC 61340-5-1管理与技术要素得策略,其她得项目也可能同时受益。这些额外得项目可能包括:  组织得责任;

 组织、转包商与供应商之间定义得角色与责任;

 监视产品产量与过程得策略可能在决定现行ESD控制测试有效性就是否恰当

与就是否需要实施额外得措施就是重要得;  确保ESD程序持续改进得方法;  批注得ESD控制产品与材料得清单;

IEC 61340-5-1得管理与技术要素需要在计划(除非裁剪)中指出,包括:  培训计划;

 遵循得验证计划;  技术要求;

 接地/连接系统;  人员接地;  保护得范围;  包装;

 标识。 4、1、5 裁剪

IEC 61340-5-1得部分可能不适用于组织得所有范围。在这种情况下,只要例外就是有效、可证实并且文件化得合理要求,组织形成文件得IEC 61340-5-1得一个或更多得要求要素得例外就是可接受得。IEC 61340-5-1可接受得例外得示例在本标准得最后ESD程序示例中。 4、2 培训计划得开发 4、2、1 人员培训

Personnel training is a critical element in the implementation of an ESD control program、 A sustained mitment and mindset among all personnel that ESD prevention is a valuable, on-going effort by everyone is one of the primary goals of training、

在实现静电放电控制程序过程中,人员培训就是决定性得要素。 在所有人员中,持久得保证与心态

静电放电预防就是有价值得,培训得主要目得之一就就是每个人都不间断得努力。

One of the first decisions that must be made is who will be required to take the ESD training course、 IEC 61340-5-1 requires that, at a minimum, initial and recurrent ESD training shall be provided to all personnel that handle or otherwise e into contact with ESD sensitive items、 This decision seems straight-forward but care shall be taken to ensure that all people that handle ESD sensitive devices receive adequate training、 One example is the finance department、 Many people will immediately state that this group should be exempt from ESD training、 However, in some panies the finance department personnel are involved in the annual physical inventory where parts are counted、 In these situations, the finance employees

are touching ESD sensitive parts and therefore must receive ESD training in order for the organization to be in pliance with IEC 61340-5-1、

第一个必须做得决定就是要求谁来参与静电放电培训课程。IEC 61340-5-1要求,至少给全体操作人员或其她方面与静电放电敏感物品有接触得人员提供最初得与周期性得培训。这个决定似乎简单,但就是必须谨慎确保所有操作静电放电敏感器件得人得到适当得培训。拿财务部门举个例子。很多人会立即说这部分群体应该不用参与静电放电培训。然而,在一些公司里,财务部门得人员会参与在零部件存放处得库存得年度盘点。在这些情况下,财务部门得员工会接触静电放电敏感零件,因此,为了组织遵守IEC 61340-5-1,她们必须接受静电放电培训。

Although it is not a requirement of IEC 61340-5-1, the organization may want to consider providing some form of ESD training to personnel who do not handle ESD sensitive parts such as:

managers, who may need to understand the implications of, and necessity for ESD prevention;

cleaning and maintenance personnel who may need to work within the EPA; and

purchasing personnel responsible for buying ESD susceptible parts and ESD equipment、

尽管IEC 61340-5-1没有要求,组织想要考虑提供一些形式得静电放电培训给那些不会触摸静电放电敏感零件人员,如:

经理,可能需要理解静电放电预防得含义与必要性;需要在EPA里工作得清洁与维修人员,与

负责购买易受静电放电影响得零件与设备得采购人员。

For visitors to the EPA, the person escorting the visitor is responsible for ensuring that they are wearing the ESD equipment required by the organization and that they understand what they may and may not do within the EPA、

对于EPA得参观者,陪同人员有责任确保她们按着组织要求穿着静电放电设备,并且懂得在EPA里哪些可以做,哪些不可以做。

Although personnel training can take several forms (i、e、 instructor, puter based, etc、), the preferred technique for initial training is through the use of an instructor、 Special care should be exercised in finding a \"suitable\" instructor、 The instructor should have a good

虽然人员培训可以采取几种形式(即面授与电脑学习等),上岗前训练应为面授。组织应为人员得培训配备专业资质得讲师。

understanding of ESD theory and the organization’s ESD control program and the processes, procedures and materials prescribed within、 In addition, if manufacturing spans more than one

culture, careful consideration shall be given to customs and religious beliefs、 Besides cultural differences, other factors such as education, experience and age should be considered、 All training should be carried out in a secure, non-threatening environment、

培训得内容应涵盖了解静电放电理论与组织得静电放电控制程序与过程,程序与材料在规定得范围内。此外,如果制造跨越不止一个化,仔细考虑,应考虑到习俗与宗教信仰。除了文化 差异,其她因素,如教育,经验与年龄应考虑。所有培训应在一个安全、无威胁得环境中进行

One of the first steps is to determine the type(s) of ESD training methods that will work best for the organization、 Some possible training methods include:

in-house, instructor-led ESD class; in-house, consultant-led class; puter based training;

industry symposia, tutorials and workshops、

第一步就是确定得类型(S)得静电放电培训方法,将工作最好 为组织。一些可能得训练方法包括: 内部,LED静电类讲师; 内部顾问领导班; 基于计算机得培训;

行业座谈会、讲座及工作坊。

The initial training program should cover the fundamentals of ESD, the details of the organization’s ESD control program plan, and each person's role in the ESD program、 The

training program should answer the following basic questions: what is static electricity? how does it occur?

how does ESD affect product quality?

A careful explanation of the protection process as part of pany policy should be included、 No matter which type of training method is chosen, the program should be designed so that all trainee questions that arise can be answered、 In addition, a knowledgeable person in the organization should be available to answer trainee questions once they have begun working、 Opening the lines of munication is the beginning of a successful ESD training program、 This type of munication should continue in the workplace and form the basis for an

ongoing education process、 It is a requirement in IEC 61340-5-1 that initial ESD training is provided before personnel handle ESD sensitive devices、

Because ESD control programs cover such a variety of job disciplines and educational levels, it may be necessary to develop special job specific training modules、 Advanced modules should emphasize the main concerns of each discipline、 Course emphasis should be tailored to each group's specific needs、 For example, the modules developed for management, engineering, technicians, cleaning staff and field service could differ significantly because their day-to-day concerns and responsibilities are much different、

Ongoing or refresher training is also vital to any organization’s training plan、 It should reinforce the basic fundamentals taught during initial training, but also should incorporate program updates and changes and the reasons for those changes、 As with the initial training, the organization shall decide which type of training will be used and how frequently the recurring training will be required、 The method chosen should keep everyone informed, renewing his or her mitment to the total ESD effort、 Recurring training is also a good feedback loop for monitoring the program’s effectiveness、 Personnel should be encouraged to

discuss issues, and make suggestions for improvement in these sessions、 Actions can then be assigned to improve the organization’s overall ESD control program、

After training (initial or recurring) sessions have been pleted, it is important to ensure that the trainee understands and has retained the ESD control program concepts taught during these sessions、 IEC 61340-5-1 requires that an objective evaluation technique be incorporated as part of the training plan、 This can be acplished in a number of ways that include written tests, question and answer sessions with an instructor or multiple choice questions at the conclusion of a puter based training session、 Regardless of the method selected, the organization should establish a pass/fail criterion for the testing to ensure adequate training has been acplished、 Records of all test results should be maintained、 The test records should be stored such that they are readily available to management and customers who want objective evidence that the training portion of the ESD control program plan is being adhered to、

Finally, since IEC 61340-5-1 requires recurring or “refresher” training, a system should be established to highlight when employees are due for retesting and/or recertification、

A repository or central information source of educational ESD control materials should be kept for reference at anytime by organization employees、 This repository might include: material from initial and recurring training sessions;

ESD bulletins or newsletters; videos or CDs;

puter-based training materials;

technical papers, studies, standards and specifications; ESD control material and equipment product sheets、 4、3 Development of a pliance verification plan 4、3、1 Introduction

This subclause will discuss the importance of having a properly implemented pliance verification plan and its role in maintaining a successful ESD control program、 In order for the ESD control program to be successful it is essential to develop a plan for ongoing

surveillance、 The plan shall identify the ESD control items that will be used,

how often the item will be checked to ensure that it meets specification and the type of audits,

the acceptable limits for each ESD control item used,

the test methods that will be used by the auditors to verify that each ESD control item is within established parameters,

the equipment that will be used to check the various ESD control items, who will make the audit measurements,

what will be done if an out of pliance situation occurs、 4、3、2 ESD control items

There are many ways to establish an ESD control program、 A program can range from a very simple, low cost or basic system to a highly plex control program that uses a variety of control items that provide redundancy in the event that the primary ESD control element(s) were to fail、

A basic ESD control program might include the following items: a) a grounded work surface;

b) personnel grounded through a wrist strap system;

c) ESD protective packaging to move ESDS from one process step to the next、 A plex ESD control program might include the following items: 1) grounded work surfaces;

2) personnel grounded through constant wrist strap monitor;

3) personnel grounded to a static control floor through ESD footwear; 4) personnel wearing grounded ESD garments; 5) air ionization at each workstation、

The decision to use a basic versus a plex ESD control program is a matter of pany

choice、 Some of the considerations are: value of the products being manufactured, product reliability requirements imposed by the customer and the ESD sensitivity of the devices being handled、 One type of program is not necessarily any better than the other as each can be effective in protecting ESD sensitive devices、

Once the ESD control items have been defined and implemented, the organization should develop an audit checklist、 In order to establish meaningful data concerning improving or deteriorating ESD program trends, it is necessary for auditors to audit each area consistently

every time、 Many organizations find that properly designed checklists help improve audit consistency、

4、3、3 Verification frequency

The frequency for checking the function of ESD control elements is dependent on a number of factors such as how often the item is used, the item’s durability and the impact on the ESD control program if the control item were to fail、 As an example, wrist straps are often used as the primary ground for personnel、 A wrist cord, whilst being worn, is subjected to thousands of stretch/bend cycles each day and the conductive wire(s) in the wrist cord will eventually break、 The typical verification frequency, used by industry, for wrist cords is once per shift due to the wrist cord’s importance to the success of the program and the likelihood of failure、 Some organizations may want to increase the time between verifications of an ESD control item after it has been in use for a period of time、 This is typically done by monitoring the failures of the ESD control item、 Once the organization has evidence that there is an acceptable period of time where no failures were found, the time between verifications can be increased、 The new verification interval is then monitored、 If an unacceptable level of failures is identified, then the verification frequency should revert back to the previous level、 4、3、4 Type of verifications

There are several types of verifications in use by industry today、 These verifications are often used in bination to maximize the effectiveness of the ESD program、 4、3、4、1 Visual verifications

Visual verifications are used by panies to check the general state of the EPA、 They can be used by employees at the start of the shift to ensure that all ground wires are in place and that unnecessary static generators have been removed from the workplace、 Visual verifications can also be used by management and supervisory personnel to ensure that employees are following organization guidelines with respect to daily testing of wrist straps, the proper wearing of ESD garments and the correct wearing of wrist straps and ESD footwear、 A visual verification is often a good indication of whether or not an ESD program is being followed、

4、3、4、2 Measurement verifications

Most organizations rely on verifying that the ESD control elements function through the use of actual measurements、 These types of verifications are carried out by specially trained auditors using equipment that has been selected to properly measure each ESD control element、 Some organizations measure 100 % of each control element in use throughout the factory while others perform verifications on a sample basis、 The type of verification used is up to the organization implementing IEC 61340-5-1 as long as it proves to be effective、 4、3、5 ESD control item limits

In the past, many panies were forced to develop their own test procedures and establish the limits for the ESD control items that they used、 However, ESD control has advanced to the

point where there are generally accepted limits for many of the ESD control items that are used、 Establishing an ESD program around the limits found in IEC 61340-5-1 will drastically reduce the possibility that 100 V (HBM) sensitive devices will be damaged by an ESD event、 There might be instances where the limits must be tightened、 An example of this situation occurs when the organization designs an ESD program around a device with an ESD

sensitivity of less than 100 V、 4、3、6 Test methods

In order to implement IEC 61340-5-1, it is a requirement that the organization follows the test methods or standards specified in Tables 1 to 4 of IEC 61340-5-1、 It is recognized that some organizations have developed their own test methods or use other standard methods for verifying some of the ESD control elements、 This is allowed under IEC 61340-5-1、 If theorganization does not use the standards referenced in IEC 61340-5-1, a tailoring statement shall be included in the ESD control program plan that describes the reason for not using the referenced standards、 The organization shall also be able to reliably demonstrate that the test methods used are suitable、

The test methods listed in the tables are intended primarily for qualifying products and materials for use by an organization、 A modified version of the test method is often used by the organization for making audit measurements that ply with IEC 61340-5-1、

It is very important that everyone involved in auditing the ESD control program understands how the audit measurements are to be made、 The organizationshall develop procedures for making each of the audit measurements、 The organization shall also ensure that everyone involved in taking measurements understands the audit procedures、 4、3、7 Test equipment

It is very important that the organization selects the proper equipment for making pliance verification measurements、 It is best to select equipment that plies with the equipment specified in the individual IEC test methods or standards referenced in Tables 1 through 4 of IEC 61340-5-1、 Each of the auditors shall be trained in how to properly use the measuring equipment、

4、3、8 Auditor skills

As part of developing an ESD program that is pliant with IEC 61340-5-1, it is important that the right people be selected to audit the ESD program、 Some considerations for selecting internal auditors include the following:

The internal auditor shall be familiar with IEC 61340-5-1 as well as the organization’s specific ESD program、

The internal auditor should also understand how the ESD control program fits into the organization’s quality management system、 ESD audit findings are one example、 How does the organization handle non-conformances found during audits? How are ESD audit findings documented? Are corrective action reports generated? Prior to closing a corrective action, does the auditor verify that the audit finding has been corrected?

It is preferred that the internal auditor has received training on how audits are conducted、 ISO 90001 auditor training provides a good basis for all process auditors、

The ESD auditor should have a good understanding of the manufacturing processes that they will be auditing、

4、3、9 Reporting of audit findings

It is important to keep management informed about the status of the ESD program、 This can be acplished through issuing reports at the pletion of an audit、 The ESD coordinator will need to classify the severity of each non-conformance、 Major non-conformances should be addressed before those considered to be minor in nature、 For significant ESD nonpliance issues, management should be notified immediately so that proper resources can

be assigned to correct the problem、

There are many ways to make management aware of the ESD findings、 Audit charts are monly used to report the audit results、 The chart, at a minimum should identify: the number of audit findings; the type of finding; the area audited、

Manufacturing line #1

Figure 1 – Example audit report showing current status of ESD program

The information contained in Figure 1 shows management the current status of the ESD program and the items that are the largest source of non-conformances、 However, Figure 1 does not tell management whether the program is being adhered to、 Many organizations establish audit targets for the total number of findings allowed in a given area、 Figure 2 includes targets for the manufacturing line、 As can be seen in Figure 2, the manufacturing line has greatly exceeded the established ESD targets、 This information further assists management in determining whether or not the ESD program is being followed、 A final enhancement to the report is an audit trend report、 This information shows management the status of the audited area over time、 An example of a trend chart can be found in Figure 3、

Manufacturing line #1

Figure 2 – Example audit report showing target for manufacturing line

Manufacturing line #1

Figure 3 – Example audit report showing audit trend report

4、4 Grounding/bonding systems 4、4、1 Introduction

The protection of ESDS is acplished by providing a ground path to bring ESD protective materials and personnel to the same electrical potential、 All conductor and dissipative items in the environment, including personnel, shall be bonded or electrically connected to a known ground or mon connection point、 This connection results in a sharing of charge which equalizes the voltage across all items and personnel and eliminates the chances of an ESD

event to ESD sensitive devices、 Electrostatic protection can be maintained at a potential different from a \"zero\" voltage ground reference as long as all items in the system are at the same potential、

NOTE It is important to understand that insulators cannot lose their electrostatic charge by connection to ground、 The handling of insulators is dealt with in 4、6 d)、

This subclause provides guidance and procedures needed to establish an effective path to ground、 This discussion is limited to grounding for ESD purposes、

4、4、2 Basic grounding requirements

The first step in ensuring that everything in an EPA is at the same electrical potential is to ground all conductive ponents of the work area (work surfaces, people, equipment, etc、) to one of the following points、

4、4、2、1 Protective earth or functional ground

The electrical ground reference (protective earth) for ESD purposes utilizes the equipment grounding conductor which is a part of the electrical power system、 Using protective earth as a ground reference for ESD control items ensures that the ESD control items and all powered electrical equipment are at the same potential、 The following diagrams (Figures 4a, 4b and 4c) show the equipment grounding conductor as it is used in three different electrical power systems、 When using this type of ground reference, the ESD control items used by an organization are connected to the equipment grounding conductor、

In situations where the organization does not wish to use the equipment grounding conductor or an equipment grounding conductor is not available, a functional ground can be used、 The functional ground is a separate earth grounding electrode that is used as the ground reference for all the ESD control items used by the organization、 It is remended that, if possible, the functional ground system be bonded to the electrical ground system (when available) in order to eliminate differences in potential between the two grounding systems、

Figure 4a – North American electrical power system

Figure 4b – Malaysia electrical power system

Figure 4c – UK electrical power system – Single phase system

Figure 4 – Country-specific electrical power systems

4、4、2、2 mon connection point (equipotential bonding)

Where a ground system is not available, an ESD control program can still be established by connecting all of the ESD control items and other large conductors together at a mon connection point、 The mon connection point is not connected to ground, but the items attached to the mon connection point will all be at the same potential, which minimizes the chance of the ESDS being damaged、 The mon connection point can be a single conductive point where the grounding wires of each of the ESD control items are attached or it cn be a large conductive element such as the metal frame of a workstation、

A real life example of this is often observed in office equipment field service operations、 For safety reasons, the service technician will often disconnect the AC power cord which detaches the equipment from ground、 In order to install ESD sensitive boards or ponents into the equipment it is necessary to electrically connect or bond together the service technician, the equipment frame and the ESD sensitive product、 Once bonded together, an ESD event will not occur between bonded items when the technician handles the product or installs it in the office equipment、

4、4、3 Additional grounding considerations

Aircraft, ships and surface vehicles typically have a ground bus or ground conductor that is suitable for use as an ESD ground、 This scenario is similar to the equipotential bonding situation、

It is a good practice for each grounded work surface to be directly connected to ground、 Figure 5 is an example of the remended method、 Many panies however connect work surfaces to ground in series as shown in Figure 6、 Connecting the work surfaces together in series can lead to a situation where multiple work surfaces bee detached from ground if the single grounding wire breaks and therefore this type of grounding method is not remended、

Figure 5 –Example of individually grounded benches – Remended

Figure 6 – Example of a series ground connection of benches – Not remended 4、4、4 Verification of ESD grounding system 4、4、4、1 Protective earth

For ESD control programs that use the equipment grounding conductor to ground the ESD control items it is necessary to verify the integrity of the electrical system、 The values used can vary depending on the electrical code requirements in each country、 However, there are certain items that should be checked for any ESD control program that uses the equipment

grounding conductor、

The impedance of the equipment grounding conductor should meet national electrical code requirements、

The electrical system is correctly wired to ensure that the ESD control items are attached to ground and not an energized portion of the electrical system、 4、4、4、2 Functional ground

When a functional ground is used it is necessary to verify that the ground rod system meets national electrical codes for such systems、 Some of the items that might require testing include: soil resistivity; resistance to gound;

resistance of the grounding electrode、 4、4、4、3 Equipotential bonding

Where an equipotential bonding system is used, it is important to verify that the mon connection point is sufficiently conductive、 The resistance of the mon connection point between any two ESD control item connections should be less than 1 when measured using a DC ohmmeter capable of measuring resistance from 0,1 1 through 1x106 1 with a minimum open circuit voltage of 1,5 V、

4、4、5 Verification of proper installation of ESD control items

Once the ESD ground reference has been verified it is important to ensure that each of the ESD control items used is connected to the ground reference、 First ensure that each ESD control item is connected to the ground reference、 Next, using the test method or standard and limits for each ESD control item given in Tables 2 and 3 of IEC 61340-5-1, verify that the resistance to ground (or to the mon connection point) meets the required limit、 4、5 Personnel grounding

Personnel grounding is a critical technical element required in IEC 61340-5-1 and shall be addressed any time personnel are involved with the handling of unprotected ESD sensitive devices、 There are two means by which this requirement can be met、 The first is by use of a

wrist strap system and the second is by use of a flooring/footwear system、 The choice is dependent on several factors that include the physical actions and surroundings of the individual as well as the potential cost of each alternative、 Both system techniques include the person, the control items (i、e、 wrist strap, flooring, and footwear) and the connection to ground、 Wrist strap, flooring and footwear types, uses, and other key information about each are described in 4、5、2 and 4、5、3、 4、5、1 System requirements

Electrostatic charge can accumulate on the body through movement、 The charge results in an

electrostatic potential or voltage between the body and ground、 This can be damaging if discharged to ESDS、 The procedures outlined in IEC 61340-5-1 are designed to protect devices sensitive to human body model voltages of 100 V or greater、 To maintain a person’s body voltage to less than 100 V, the body shall be electrically connected to ground or differences in potential shall be eliminated by bonding all of the ESD control elements together、

With a grounded system, there shall be some degree of assurance that the body voltage remains below 100 V when connected in series with a resistance to ground、 This resistance is a key factor in limiting the voltage observed on the body、 For a given body movement, the voltage achieved increases with resistance、 Tests conducted by IEC technical mittee 101 have shown that a resistance of 3, 5 x107 or less is necessary to limit body voltage to less than 100 V、 Figure 7 shows the relationship between body voltage and resistance to ground、

Figure 7 – Relationship between body voltage and resistance to ground

4、5、2 Wrist strap system

A wrist strap system consists of three elements: the person, the wrist cord and a wrist band、 To ensure that the resistance to ground of personnel is within the specifications, it is

important to measure the entire system (i、e、 from the person’s body to the end of the ground cord)、

A wrist strap assembly is the most monly used means of grounding personnel、 A wrist strap is required in IEC 61340-5-1 for operations where the individual is seated while handling or processing ESD sensitive items or ponents、 The reason for this requirement is that floor and footwear systems may not provide reliable contact with ground since the person’s feet may not be in contact with the floor at all times while seated、

While a wrist strap assembly will ground a person when standing, often the grounding cord will bee a physical impediment to the wearer、 In these situations organizations will often rely on a flooring footwear system to ground their employees、 4、5、3 Footwear-flooring system

Personnel may also be grounded through use of a flooring and footwear system、 This method is useful when personnel require mobility or stand in areas where wrist straps are not feasible and ESDS items must be handled or transported、 The ground path is maintained through the use of dissipative or conductive floors and dissipative or conductive footwear、 Footwearflooring

systems may be installed to provide a back-up ESD control item for personnel grounded with a wrist strap system、

When footwear-flooring systems are used as the only grounding system for personnel, the resistance to ground including the person, footwear and floor shall be the same as specified for wrist straps (< 3,5 x 107 ) at all times、 If a higher resistance footwear-flooring system is used the total resistance to ground shall be less than 1,0 x109 and the maximum voltage on a person shall be less than 100 V (average of the five highest peaks) under worst case conditions、

Some of the ESD footwear options include ESD control shoes, sole and heel grounding straps and shoe covers、 If the ESD footwear does not pletely cover the underside of the foot charge generation may occur, especially when a person is walking、 An example of this occurs with the use of heelstraps、 The following chart (Figure 8) shows the voltage on a person’s body as they walk across a grounded conductive floor while wearing two heelstraps、 The voltage on the person’s body is not controlled because the heelstrap is not in continuous contact with the conductive flooring surface、

Figure 8 – Voltage reading on person walking across grounded conductive floor whilst

wearing two heelstraps

Heelstraps can still be an effective part of an ESD control program when used for standing operations providing a strap is worn on each foot, and the ESD risk due to occasional loss of the ground connection is assessed to be acceptable、 They should not be used in any process where unprotected ESDS are transported inside the EPA by hand、

Two test methods are used to measure the footwear-flooring system in bination with a

person、 IEC 61340-4-5 was developed to measure:

a) The electrical system resistance of floor materials in bination with a person wearing static control footwear、 This test can be used to evaluate systems prior to installation or it can be used with installed floors、 This test method can be used to characterize any ESD protective floor material、 These include all floor coverings (e、g、 tiles, carpets, epoxies, laminates, mats, paints/coatings or floor finishes)、

b) The second test method provides a way to characterize the ESD behaviour of floor materials and footwear by measuring the charge generation of the floor, footwear andperson as a system、 This test method can be used to evaluate systems prior to

installation or it can be used with installed floors、 This test method can be used to characterize any ESD protective floor material、 These include all floor coverings (e、g、 tiles, carpets, epoxies, laminates, mats, paints/coatings or floor finishes)、 4、6 Protected areas (EPA)

An ESD protected area (EPA) is an area that is equipped with the ESD control items required to minimize the chance of damaging ESD sensitive devices、

In the broad sense, a protected area is capable of controlling static electricity on all the items that enter that work area、 Personnel and other conductive or dissipative items shall be electrically bonded together and connected to ground (or a mon connection point when a ground is not available) to equalize electrical potential among the items、 The size of an EPA can vary greatly、 A protected area may be a permanent workstation within a room or an entire factory floor enpassing thousands of workstations、 A protected area may also be a portable worksurface or mat as used in a field service situation、

IEC 61340-5-1 places several requirements on the handling of ESDS devices as follows: a) ESD sensitive devices shall be handled inside an EPA、 This means that at any operation where unprotected ESDS are handled, all of the items that potentially could e into contact with ESDS shall either be connected to the defined ESD ground or connected together to form an equipotential bond、 If the ESD sensitive device must leave the EPA, it shall be protected from damage、 ESD protective packaging or specially designed carrier can be used to transport ESDS devices from one EPA to another、

b) An EPA shall have a well defined boundary、 Appropriate signs and markings shall identify protected areas so that all people entering the area, including visitors, are aware that special precautions are needed、 Some examples of appropriate signs/markings are physical signs, floor tape outlining the border of the EPA, different coloured floor tiles or any other method that defines the border of an EPA、 The organization shall ensure that ESD awareness training clearly describes to the new employee the rules for the EPA and how it is identified、

c) Access to the EPA is restricted to personnel who have successfully pleted ESD

training、 In situations where suppliers, customers, new employees or other visitors need to enter into the EPA, they shall be escorted by a person who has pleted ESD awareness training、

d) The organization shall ensure that non-essential insulators are removed from all EPAs、 Insulators required as part of the manufacturing process shall be checked to determine whether or not they pose a threat to ESD sensitive devices、 IEC 61340-5-1 has identified two methods that are currently used throughout the world for handling process required

insulators、

1) Some organizations measure the strength of the electrostatic field at the point or position where ESDS are handled、 In this situation, the field strength shall not exceed 10 000 V/m、

2) Other organizations measure the field on the individual items that are brought into the EPA、 In these situations the electrostatic potential of the item is measured at a pre-set distance from the insulator (per the meter’s operating instruction)、 For this type of measurement the maximum acceptable potential is 2 000 V、 If the measurement exceeds 2 000 V, then one of the following must occur:

i) the insulator shall be kept a minimum of 30 cm from the ESDS;

ii) if it is not possible to maintain the 30 cm distance, the organization will use ionization or other methods to reduce the levels of charge generated in the process、 The use of chemical treatments on the surface of insulating materials or the addition of humidity controls inside the EPA are two possible methods, in addition to ionization, that can be used to reduce the levels of measured electrostatic fields to acceptable levels、 4、7 ESD control items

The following subclauses describe some of the various ESD control items that can be used when developing an ESD control program that is pliant with IEC 61340-5-1、 4、7、1 Work surfaces 4、7、1、1 General remarks

Work surfaces play a critical role in the design and implementation of an EPA、 Work surfaces designed for ESD control are used in production and repair areas as well as in field service、 Most areas where unprotected ESDS are handled, repaired or tested require some form of a work surface designed to dissipate electrostatic charges、 The work surface is a major ponent in establishing a local static safe work environment、 The work surface is considered by most of the industry to be the second most important element of an ESD control program, personnel grounding being most important、

The main purpose of a properly grounded work surface is to ensure that the items being handled and the work area are at the same electrical potential、 Work surfaces provide the following functions:

a work surface designed for control of static electricity provides an electrical path to ground or a mon connection point in the case of an equipotential bonding situation、 This allows non-insulative items placed on the work surface to discharge in a controlled manner;

the work surface in some cases may define the boundary of an ESD work area in which ESDS can be handled、

4、7、1、2 Factors in selecting work surfaces

There are several factors to be considered in selecting an appropriate work surface、 The major factors are the following: work area activities;

permanency of the work area; physical considerations; chemical considerations;

electrical considerations; safety considerations; material maintenance、

4、7、1、2、1 Work area activities

The type of work being performed at the location will determine the type of work surface that is required、 If the items being handled are sensitive to mechanical shock, then a cushioning work surface material may be required、 If heavy products with sharp edges are moved around the work surface, then a more durable surface may be necessary、 Operations where personnel are exposed to high voltages may require the use of work surfaces that will limit the current if the power source es into contact with the work surface、 Work surfaces used in cleanrooms may also require special consideration, including particulate contamination and outgassing properties、 Flammability of work surface materials may need investigation to satisfy corporate requirements, insurance carriers, or safety ratings、 4、7、1、2、2 Permanency of the work area

In selecting work surface materials a good understanding of the operation is necessary to ensure that the correct materials are selected、 Considerations include the following: Field service activities often necessitate a pletely portable work surface that may fit in a tool kit or pocket of a field service engineer、 This work surface shall be designed so that it can withstand continual handling and frequent connection and disconnection from ground、 The work surface might also need to last for years in the service engineer’s tool kit、

Conformal coating chemicals, when used on a work surface, can increase the surface’s resistance to ground to the point where the work surface may no longer function、 For these situations a disposable work surface might be more cost effective、 4、7、1、2、3 Physical considerations

Most work surfaces require a degree of durability、 Durability factors that should be considered are hardness, abrasion resistance and tear resistance、 Some work surfaces may require special heat-resistant materials、 Soldering stations, for example, may need work surfaces designed to resist heat、

Appearance is often an important factor in selecting a work surface、 Colours also may be used to distinguish specific operations or establish corporate identity、 Light reflection may be an important ergonomic consideration、 Portable work surfaces should lay flat on the substrate、

Curling with age should be a characteristic that is investigated during the qualification process、 Functionality, durability and reliability of the work surface grounding system should be evaluated during qualification testing、 4、7、1、2、4 Chemical considerations

Chemical transfer from the work surface may cause contamination that could lead to corrosion of sensitive metallic parts、 Solvents and other chemicals handled at the workstation may have deleterious effects to the work surface、 The work surface material should be evaluated for required patibility during the qualification process、 4、7、1、2、5 Electrical considerations

The most important functional consideration for work surfaces is the resistance from the top of the surface to the groundable point、 This establishes the resistance of the primary path to

ground for items placed on the surface、 IEC 61340-5-1 has set a resistance to ground range for work surfaces of less than 1,0 x 109 、

However, it is sometimes necessary to use work surfaces that are much more conductive、 This is allowed under IEC 61340-5-1 but the reasons for using a more conductive work surface shall be documented in the ESD control program plan、 4、7、1、2、6 Safety considerations

Workstations with hazardous electrical potentials may require significantly different electrical properties、 The resistance to ground and resistance point-to-point values may need to be increased where line voltage is present、

NOTE DC resistance measurements might not be adequate for making safety decisions、

4、7、1、3 Types of work surface materials

A wide variety of work surface materials and forms exist, with more being developed all the time、 The properties of these different materials vary (mechanical, physical, and electrical)、 Even though there are many varieties of work surfaces, two basic classes of work surface materials are available、 These basic classes are generally called mono-layer and multi-layer、 Some work surfaces, particularly mono-layer and high pressure laminates, may have some degree of humidity dependence、 These materials should be tested for adequate performance at low humidity prior to selection and installation、 4、7、1、3、1 Mono-layer work surface materials

Mono-layer or homogeneous work surface materials are those that have the same electrical and physical properties throughout the bulk of the material、 Rigid surfaces and flexible mat type materials are available in different resistance ranges、 Point-to-point resistance (Rp) and resistance to ground (Rg) measurements may change with distance between the electrodes or between the electrode and the groundable point of the work surface、 4、7、1、3、2 Multi-layer worksurface materials

Multi-layer worksurface materials typically consist of 2 or 3 distinct layers、 The top surface is normally a layer of dissipative material, varying, by product, in thickness and electrical properties、 The next layer is generally highly conductive、 Some forms have a bottom layer that

is made from either insulative or dissipative materials、 Electrical resistance from point-to-point and resistance to ground are generally consistent, regardless of the distance between electrodes or between a single electrode and the worksurface’s groundable point、 The controlling factor is the vertical resistance through the top surface to the conductive layer、 Proper connection of the groundable point hardware to the conductive layer is critical to assure proper charge dissipation、 4、7、1、3、3 High-pressure laminates

These materials are rigid and are applied to a substrate, typically with adhesive systems、 The majority of these materials follow the multi-layer description above、 There are, however, some

types that are basically homogeneous in construction、

Because the electrical properties of many high-pressure laminates have some degree of humidity dependence, all high pressure laminate materials should be carefully tested for adequate performance at low humidity prior to selection and installation、 4、7、1、3、4 Mat and runner (rolled) materials

Mat and runner materials are generally flexible systems that are used to cover non-ESD control substrates、 Another mon application is to use mats on top of ESD control highpressure

laminates to provide a less humidity-dependent surface in environments where

relative humidity varies by season、 Mats and runners are available in a range of resistance values and in homogeneous and multi-layer types、 4、7、1、3、5 Field service/portable work surfaces

Portable work surfaces in a variety of forms (multi-layered or homogeneous) are available to meet established requirements and the same ESD control needs as those used in non-remote areas、 Typically, field service work surfaces are designed to fold up and fit in a tool kit or a pocket of a field service engineer、 4、7、1、4 Testing

A procedure that can be used for testing the electrical resistance of work surface materials can be found in IEC 61340-2-3、 Use the test method described for making resistance to ground or groundable point measurements、 4、7、1、4、1 Evaluation

As part of the selection process, work surface samples are often evaluated under laboratory conditions where items such as humidity, temperature and test voltage are controlled、 Resistance is measured at test voltages of 10 V and 100 V at moderate and low humidity、 4、7、1、4、2 Initial installation or acceptance

When first installed, the work surfaces should be tested to make certain that they are

functional and meet specifications、 Typically, the resistance from the top of the work surface to ground is measured to ensure that the work surface has been properly installed、 Verifying that the work surface is connected to ground should be carried out before ESD sensitive devices are handled on the work surface、 If evaluation testing is not performed, it is remended that point-to-point resistance measurements be made in order to understand the characteristics of the material、 4、7、1、4、3 Periodic tests

Periodic testing of work surfaces is necessary to ensure that they continue to meet

specifications、 Resistance to ground measurements are typically used to verify that the path to ground is intact、 In cases where the resistance to ground measurement exceeds the established resistance limits, the following steps can be taken to identify the cause of the high resistance readings:

Verify visually that the work surface is connected to the ground reference、

Clean the work surface、 Sometimes a dirty surface can cause the resistance to exceed acceptable limits、 Once the surface has been cleaned (note: clean the bottom of the resistance measuring electrode as well) repeat the resistance to ground measurement、 If the second measurement is within specification this might lead to a further investigation concerning the cleaning practices used by the organization、

Disconnect the grounding wire and measure the resistance from the top surface of the work surface to the work surfaces groundable point、 This measurement shall show whether or not the work surface is functioning as designed and it will verify that there is a good connection between the groundable point and the work surface、

Using an ohmmeter, measure the resistance of the wire used to ground the work surface、

The measurement is made from the point where the wire is connected to the work surface’s groundable point to the ground reference、

The frequency of periodic testing is normally specified in corporate operating procedures、 However, a mon guide would be to conduct these measurements at least quarterly、 4、7、1、5 Maintenance

Periodic cleaning, following the manufacturer's remendations, is required to maintain

proper electrical function of all work surfaces、 Ensure that the cleaning products used do not leave an electrically insulative residue which is mon with some household cleaners that contain silicone、 4、7、2 Wrist straps 4、7、2、1 Introduction

The wrist strap is a device used to keep personnel at the same electrical potential as the ESD sensitive item(s) they are handling、 In most cases this is effected by a connection of both the person and ESDS to ground or to a mon connection point when an equipotential bonding system is used、 This subclause covers practical information for the use, care and periodic checking of wrist straps、 4、7、2、2 Wrist strap

Wrist straps typically consist of a wrist band which makes contact with the wearer’s skin、 The wrist band is then attached to a grounding cord which is connected to the ESD ground reference、

4、7、2、2、1 Wrist band

The wrist band is a flexible, form-fitting device designed to make a reliable continuous connection to a person's wrist、 Bands are manufactured in many types as summarized in Table 1、

Wrist strap bands almost always have a hypoallergenic metal plate, usually stainless steel, under the buckle or snap head to ensure good skin contact、 The remainder of the band shall also have a conductive skin-contacting surface、 This ensures that there is plete 360° of contact between the band and the person’s skin、

Wrist bands may have a quick-parting, electrical-mechanical connector that mates with a corresponding connector on the head of the ground cord、 This connector serves two purposes、 First, it is a physical connection for attaching the ground cord、 Second, it is the groundable point on the band、 Quick release is an important feature of the connector、 The breakaway force should be low enough to allow easy release, but high enough to prevent unintentional disconnection、 If the breakaway force is too light, the ground connection could be lost without the knowledge of the wearer、 Experience has shown that for conventional, single-conductor wrist straps, connectors that part with a force of 13 to 36 newtons are satisfactory、

When initially selecting wrist straps or when reordering for an existing program, it is a good practice to specify a patible snap size and orientation、 This allows for patibility between existing wrist straps and new purchases、 Many wrist strap manufacturers will customize the snap connector configuration to suit the user's requirements provided there is sufficient quantity、

Table 1 – Type of wrist strap bands

Woven elastic fibre with conductive fibres on the inside surface

Knit elastic fabric with conductive fibres on the inside surface Woven non-elastic fabric having a conductive inside surface Metal expansion bracelet with insulating resin on the outside surface Plastic resin wrist watch band with stainless steel sheet metal strips on the inside surface

Shaped sheet metal bracelet with insulating resin on the outer surface Electrode patch with conductive adhesive

4、7、2、2、2 Wrist strap ground cord

The ground cord is a wire assembly that connects the wrist band to ground or to a mon connection point、 It usually consists of an insulated wire with a connector head that attaches to the band on one end and a termination device on the other end for connecting to ground、 Ground cords usually contain a current-limiting resistor at the band-connecting end、 At first glance, the ground cord appears to be a relatively simple assembly、 However, the design requirements are considerable, given the wide range of user applications and the durability requirements of constant tugging, flexing and dragging over the edge of workstation tops and equipment chassis、

Ground cords are available in varying lengths, straight wire or retractable coil cords, resistors in one end or both ends, various colours and several types of ground termination devices、 The

wire can be multi-stranded linear or helical wound tinsel、 The insulation can consist of a durable polymer, a tough synthetic rubber or vinyl、

Any electrical connector that can be attached to ground is acceptable as long as it is

mechanically durable、 The preferred grounding point for the groundable end of the cord is a point connected to ground or to a mon connection point、 (See 4、4、2 for further information、)

NOTE Many wrist strap users have been observed to clip the wrist cord to the edge of an ESD protective mat、 This process is not remended as it can increase the total system resistance to ground to over the 3,5 x 10limit required by IEC 61340-5-1、

4、7、2、3 Wrist strap use and selection

The wrist strap is an effective system for grounding people who handle ESD sensitive materials、 However, it is important to emphasize that while the wrist strap grounds the skin, it does not provide a means to eliminate static charges from clothing and footwear, unless these items are conductive or dissipative and make contact with the person’s skin、 4、7、2、3、1 Use

For maximum effectiveness, wrist straps should be used properly following these guidelines、 The wrist strap band should fit snugly and make full skin contact around the wrist、 The wrist band should not be worn unfortably tight and should not leave deep marks on the wrist、

The wrist strap shall be connected to a ground or a mon connection point、 A continuous and secure connection will provide the proper dissipation of electrostatic charges stored on the body、 4、7、2、3、2 Wrist strap selection

The following factors should be considered when selecting and evaluating wrist straps、 Reliability

Durability

Length of the ground cord

Retractable ground cord or straight Snap configuration

Ground termination connector fort

Human fort plays a major part in the selection of a wrist strap design since the wrist strap has to be worn continuously、 It should not detract from the efficiency of any work function、 There are numerous designs that incorporate various techniques for providing reliable skin contact、 These wrist straps range from fabric woven with conductive fibres to metal flexible bands or other special use designs、 The ultimate selection will be up to the user since it must be patible with the process、 4、7、2、4 Wrist strap testing

Because wrist straps do not last forever, they should be tested periodically、 A good testing program not only tests the wrist strap itself, but also indicates the quality of the skin contact when performing a system test、 Wrist strap bands that are soiled, incorrectly sized or improperly worn will show resistance higher than acceptable、 Changes in weather and people can affect ground resistance、 Dry skin often leads to high resistance indications、 4、7、2、4、1 Reliability testing

A major factor in selecting and using wrist straps is reliability、 Stress testing to predict reliability is expensive and best performed by a qualified laboratory、

Analysis of the wrist strap to determine the nature of the failure can be useful、 Areas of concern include skin contact failure, cord failure and connector failure、 By collating the data on a periodic basis, it is possible to determine trends for particular manufacturers and styles、 This information will be useful when making further purchasing decisions、 Use of wrist straps that exhibit inadequate life span should be discontinued, regardless of the failure mode、 4、7、2、4、2 Additional user wrist strap testing

The testing described here is more than a test of a wrist strap; it is also a test of the quality of the connection the band makes with the wrist、 It is a test of the wrist strap in an ‘as used’ configuration, referred to as a system test、 The purpose of testing the wrist strap as a system is to confirm that the total series resistance of all of the elements in the system is between the minimum and maximum resistance allowed by the user's specification、

Proper testing of the wrist strap includes the resistance of the groundable point on the end of the cord, the cord itself, the current-limiting resistor, the cord-to-band snap connector, the resistance of the interface of the cuff, the cuff/wrist interface, and the resistance of the person between the wrist and the hand that contacts the test electrode、 The maximum acceptable resistance for wrist strap grounding is less than 3,5 x107 、 There are many mercially available wrist strap checkers to perform this system test、 Some have the added capability to test the cord alone、 When selecting a wrist strap checker, it is important to read the specifications to see if the upper and lower resistance limits of the checker match the user’s requirements、 On some wrist strap checkers, one or both limits may be adjustable、 In use, these checkers will indicate if the system resistance is below, above, or within the acceptable range、 Some testers will only indicate whether the system resistance is within the acceptable range or outside it、

A system test can also be performed using an ohmmeter as long as the test potential is safe、 A metal electrode that can be held in the hand is attached to one of the meter leads、 Holding a pin probe tip between fingertips can produce erroneous results、 When using an ohmmeter to

perform this test, it is important to understand that the resistance of the human is considered in the total resistance of the system and that the value of this resistance will vary from person to person、

4、7、2、4、3 Test procedure

While wearing the wrist strap, connect the loose end of the cord to the tester terminal and depress the test button or touch the metal test surface with a finger or hand、 If the resistance is over 3,5 x107 , test the cord alone for continuity、 If the resistance of the cord alone is approximately 1,0 x106 , check the fit of the band around the wrist and adjust it for a snug fit、 Snap the cord back on the cuff and retest、 If the resistance is still over 3,5 x107 , substitute a new band、

NOTE 1 Electrical breakages within the cord can be checked by flexing the cord during measurement、

If the resistance is still too high, dry skin might be the problem、 Dry skin conditions can be resolved by applying moisturizing lotion on the wrist and repeating the resistance test again、 The moisturizing lotion should be one that is patible with process requirements and does not cause contamination、

NOTE 2 Metal expansion bracelet style wrist bands may trap moisture underneath and can be more effective for people with dry skin、

4、7、2、4、4 Test frequency

Wrist straps should be tested periodically、 The frequency of testing, however, is driven by the amount of usage, wear and ESD risk exposure that can occur between tests、 For, example, what is the quantity of product handled between test periods?

Because wrist straps have a finite life, it is important to develop a test frequency that will guarantee integrity of the system、 Typical test programs remend that wrist straps that areused daily should be tested daily、 However, if the products that are being produced are of such value that a guarantee of a continuous, reliable ground is needed then continuous monitoring should be considered or even required、

Data taken from the test program will ultimately allow the user to make the choice of how often the wrist strap should be checked and which wrist straps have the most useful service life、

4、7、2、5 Current limiting

Wrist straps have a current limiting resistor moulded into the ground cord head on the end that connects to the band、 The resistor most monly used is a 1 x 106 , 1/4 watt with a working voltage rating of 250 V、 Resistors limit current as defined by Ohm's Law, which states the current is equal to the voltage divided by the resistance、 In a practical application, the maximum amount of current through a wrist strap ground cord if it is placed across a 250 V source, is 250 A or 0,25 mA、

For personnel safety, wrist straps incorporating a 1,0 x 106 resistor should not be used in situations where there is an exposed electrical circuit of 250 V or higher、 Some additional options for high voltage operations are as follows:

Select a wrist strap system that utilizes a higher value resistor、

Intentionally isolate the operator from ground through the use of high resistance floor mats or gloves、

NOTE Several publications exist that provide varying limits of allowable current for personnel safety、 For

example, most power supplies are current limited to 5 mA、 For this reason, the user should check with local safety personnel to determine requirements for their particular area、

4、7、2、6 Summary

Wrist straps provide an effective means for maintaining personnel at ground potential or at the same potential as the item(s) being handled、 People who are at ground potential or a potential the same as the ESDS they are handling cannot discharge to the ESDS when it is handled or touched、

Wrist straps usually have a current-limiting resistor, typically 1,0 x106 , molded into the ground cord near the point where the cord attaches to the cuff、 The resistor usually has a working voltage rating of 250 V、

Wrist straps are sometimes supplied with a 1,0 x 106 resistor molded into both ends of the ground cord when both ends of the cord have the same type snap connector、 Wrist straps should not be worn by personnel where they could e into contact with voltage over 250 V、

Wrist strap ground cords should have a quick release connector to the cuff so personnel will not be tied to the workstation、

Wrist strap bands should be worn fortably snug around the wrist while making full skin contact、

Wrist strap ground cords shall be connected to a groundable point or an equipotential bonding point、 Do not connect to a snap on a dissipative mat unless it is the groundable point for the mat、 Do not clip a wrist strap to the edge of a dissipative mat、 Wrist straps should be tested on a regular basis with daily testing being remended、 4、7、3 Static protective floor materials 4、7、3、1 Introduction

The principal cause of static electricity is frequently cited as the movement of people and materials in the work environment、 This routine movement, particularly the contact and separation of shoe from floor, generates charges as high as several thousand volts、 Similarly, the movement of mobile carts or other equipment will generate electrostatic charge、 Thissubclause will review the use of floor materials to dissipate electrostatic charge、 It will cover

floor coverings, floor finishes, topical anti-stats, floor mats, paints and coatings、 4、7、3、2 Functions of static protective floor materials

Static protective floor materials are used in the electronics industry for:

Grounding of personnel (floor materials can be used in bination with static control footwear as either a primary ground or a secondary, backup system, ground for wrist straps in critical ESD processes)

Grounding of ESD control items such as: – mobile carts,

– ergonomic stands used to raise the product to an employee’s working height , – workstations、

Floor coverings, mats, paints and coatings help control static charge by providing a path of

moderate electrical conductivity from the human body or ESD control item to ground、 Many flooring products use a conductive material, such as carbon, metal or other additives, that extends from the surface of the material to an underlying substrate such as conductive adhesive、 The floor material is then connected directly to ground、

Floor finishes and topical anti-stats, on the other hand, function by two separate mechanisms、 First, they reduce the surface's tendency to generate a static charge、 Second, they provide a path for the dissipation of charge、 If the floor finish or topical anti-stat is used for primary grounding they shall be able to limit charging while dissipating it to ground、 4、7、3、3 Relationship between floors and footwear

Grounding through the floor is dependent on the type of footwear that is in contact with the floor、 Typical street shoes or industrial footwear with rubber, crepe, or polyurethane soles insulate the wearer from the floor、 Generated charges cannot readily flow from the body, through the insulated shoe sole to the floor material to ground、

Studies of ESD control floor materials indicate that charge generation and charge decay times as measured on a person's body vary with the type of footwear worn、 The levels of performance depend upon the bination of floor material and footwear、 The proper selection of footwear is critical to the performance of static protective floor materials、 4、7、3、4 Benefits of floor materials

The use of floor materials to control personnel or equipment generated static has a number of benefits、 Floor materials tend to be passive、 Employees who work in areas protected with floor materials simply need to wear and test the appropriate footwear、 They do not need to implement any additional actions themselves to assure that the floor material is functioning properly、

Floor materials, particularly floor coverings, finishes, and coatings, can be applied or installed throughout the work environment providing a broad area of control rather than isolated control at individual workstations、 They improve the mobility of personnel who work in the environment、 Finally, floor materials can help control static on trolleys or other mobile equipment if properly grounded、

4、7、3、5 Limitations of floor materials

Floor materials also have some limitations、 When used to ground people, the person shall maintain contact with the ESD control floor、 In order to do this the person must be standing、 This is the primary reason that IEC 61340-5-1 requires a wrist strap for seated operations、