Using a current limiting resistor in the ground cord is the user’s choice; however, the resistor is not for ESD control purposes. Either without resistor or with a one megohm resistor is acceptable, but most all Charleswater ground cords do contain a resistor at the snap end.
Here is advice from our industry’s standard:
“An easily accessible dedicated EBP [EPA ground bonding point] for the wrist strap shall be established adjacent to each working area, or working surface. A sufficient number of EBP shall be provided for operators and visitors.” (EN 61340-5-1 section 5.3.3)
“EPA ground cords shall be used to make electrical connections between groundable points and the EPA ground facility.” (EN 61340-5-1 section 5.3.4)
Regarding 1 megohm resistor, “A nominal 1 megohm resistor is commonly used in wrist straps and to ground work surfaces.” [EN 61340-5-2: Section 5.1.1] However, for Working Surfaces, it refers to “it is allowed, when approved by the ESD coordinator, to use surfaces which are “hard ground” i.e. less than 1 X 10^4 ohms to EPA ground.” (EN 61340-5-1 Note 6 of Table 1)
“The EPA ground facility shall be connected to EPA ground and provide a low resistance path to EPA ground (<2 ohms). When available, the mains protective earth shall be used. (EN 61340-5-1 section 5.3.2)
When an in-line resistor is used in Charleswater’s common point grounds it is isolated from the banana jacks
From ESD User guide CLC/TR 61340-5-2:2008 clause 4.1:
This clause outlines a step-by-step approach that can be used to establish an ESD control program.
4.1 Developing an ESD control program plan
4.1.1 Assignment of an ESD coordinator
In order to have a well thought out and implemented ESD program an ESD coordinator must be assigned. The ESD coordinator is responsible for all aspects of ESD in the facility. In order to be effective the ESD coordinator needs:
- the full support of management
- a good understanding of electrostatics and how ESD sensitive devices can be damaged. The ESD coordinator will often need to attend educational classes or seminars related to ESD in order to maintain or update their knowledge
- a thorough understanding of IEC 61340-5-1 and all of the organization’s processes related to the handling of ESD sensitive devices
- access to measuring equipment for the purposes of performing compliance verification audits as well as testing new ESD products and materials for use in the ESD program
- depending on the size of the facility, the ESD coordinator might also need to have auditors assigned to conduct the ESD audits
Finally, management must provide the ESD coordinator with the authority and funding necessary to ensure that the ESD control program is maintained and enforced.
4.1.2 Determination of part ESD sensitivity
The next step in developing an ESD control program plan is to determine the part, assembly or equipment sensitivity level under which the plan is to be developed. Although the requirements outlined in IEC 61340-5-1 are effective for handling parts sensitive to 100 V HBM or higher, the organization may choose to develop an ESD program based on ESD sensitivities that are greater or less than 100 V HBM. In this situation, the organization must develop an ESD control program plan that clearly states the ESD sensitivity that the program is based on. The organization can use various methods to determine the ESD sensitivity of the products that are to be handled. Some of the methods include: assumption that all ESD products have an HBM sensitivity of 100 V; actual testing of ESD sensitive devices to establish the ESD sensitivity thresholds using IEC 60749-26; referencing ESD sensitivity data in published documents such as manufacturer’s published data sheets.
4.1.3 Initial process and organizational assessment
Before the ESD control program plan can be developed, an initial assessment of the processes and organizations impacted by an ESD control program should be conducted. Organizations and processes that might be affected include:
- design engineering
- receiving inspection
- quality assurance
- packaging and shipping
- field service
- failure analysis
- repair services
- spare parts storage
- material handling and parts conveyance
An assessment of each area where ESDS parts are handled should be conducted in order to determine ESD hazards and possible ESD process procedures. The information accumulated throughout these steps forms the basis for developing the ESD control program plan.
4.1.4 Documentation of ESD control program plan
After gathering the above information, the organization is in a position to begin documenting the program plan. The plan should state the scope of the program which includes the tasks, activities and procedures necessary to protect the ESD sensitive items at or above the ESD sensitivity level chosen for the plan. Although the primary focus of the plan is to outline strategies for meeting the administrative and technical elements of IEC 61340-5-1, other items may be beneficial to incorporate as well. These additional items might include:
- organizational responsibilities
- defined roles and responsibilities between the organization and subcontractors and suppliers
- strategies for monitoring product yields and processes that might be important in determining the effectiveness of ESD control measures currently in place or in assessing whether additional measures should be taken
- approaches for ensuring continual improvement of the ESD program
- a list of approved ESD control products and materials.
The administrative and technical elements of IEC 61340-5-1 that need to be addressed in the plan (unless tailored) include:
- training plan
- compliance verification plan
- technical requirements
- grounding bonding systems
- personnel grounding
- protected areas
Charleswater – your ESD Control Experts. Contact Customer Service for help with your ESD Control Programme.