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Question

Good Morning Sir,

I have 2 questions about paper use in ESD Protected Area and 1 question about table grounding and seek your advice as below:

In our manufacturing floor, paper are used as a reject tag, debug printing result, checklist or ID tag which in contact with the pcba. Our manufacturing floor is control at 30-65 % RH.

Question 1: Can papers at this environment be a treat or can cause damage to ESD sensitive component on the circuit board?

Question 2: How about paper use to print result after test procedures? Is the paper will hold a static charge create by a printer roller and good enough to cause damage to the sensitive components after wrap on the pcba?

Before you answer me, let me brief a bit about my manufacturing EPA. The floor tile is dissipative range (10^6 to 10^7), all workbench is grounded + with dissipative esd mat installed on table surface and people garment with smock, esd shoe and wrist strap. Dissipative glove use to hold the pcba all the time at any station in EPA.

Question 3: My table is made by metal fabrication and accommodate with wrist strap jack and 3-prong socket for equipment grounding and a layer of esd mats on top of table surface with clip & screwed at the edges of the table but one thing I do not install is a 1 Meg resistor at the wrist strap jack. The reason behind is I already have 1 meg ohm resistor build in to wrist strap instrument and all my common ground point to equipment ground is below 1.0 ohm AC. So questions to you will be:

Do I need to:

    1. Install 1 Meg resistor at the wrist strap jack?
    2. If I have equipment such as LCR meter on the table, is there any chance for me to get electric shock if happen to have leakage?
    3. Is my table grounding safe to use?

Your respond is very much appreciated and have a good day.

Best Regards,

Hafizal.

Answer

Question 1: Can papers at this environment be a treat or can cause damage to ESD sensitive component on the circuit board?

Answer: Paper is not typically a serious threat to ESD sensitive items. However, best practice is to use Dissipative Paper or have regular insulative paper in Dissipative Document Holders.

Regular paper is insulative, and the concern is placing ESD sensitive items on the paper interfering with the path-to-ground of the grounded ESD mat. However, paper is hygroscopic (readily absorbing moisture) so often there is sufficient moisture to provide an acceptable path-to-ground. If regular paper is used, discipline not to place the ESDS on the paper should be followed particularly during periods of low humidity.


Question 2: How about paper use to print result after test procedures? Is the paper will hold a static charge create by a printer roller and good enough to cause damage to the sensitive components after wrap on the pcba?

Answer: Coatings on the paper used in a printer may generate higher levels of electrostatic charges. You should measure the charge using a Static Field Meter.


Question 3: My table is made by metal fabrication and accommodate with wrist strap jack and 3-prong socket for equipment grounding and a layer of esd mats on top of table surface with clip & screwed at the edges of the table but one thing I do not install is a 1 Meg resistor at the wrist strap jack. The reason behind is I already have 1 meg ohm resistor build in to wrist strap instrument and all my common ground point to equipment ground is below 1.0 ohm AC. So questions to you will be:

Do I need to:

    1. Install 1 Meg resistor at the wrist strap jack?
    2. If I have equipment such as LCR meter on the table, is there any chance for me to get electric shock if happen to have leakage?
    3. Is my table grounding safe to use?

Answer:

The ESD Association recommends hard ground for the ESD wrist strap grounding point. As you note, there is a current limiting resistor in the wrist strap cord. “The resistance of the conductor from the groundable point ground of any ESD technical element (e.g. worksurface, floor, chair, wrist strap, etc.) to the common point ground or common connection point shall not be greater than 1 ohm. Where a resistor is used in the grounding conductor, the total resistance shall include the value of the resistor.” [Grounding ANSI ESD S6.1 section 6.4.1]

We can provide ESD control expertise; safety questions should be directed to your safety officer. ESD Systems personnel grounding products are Underwriters Laboratory listed. UL Notes: “This product is not recommended for use on equipment with operating voltage exceeding 250 VAC.

CAUTION: The ESD Series is for electrostatic control. It will not reduce or increase your risk of receiving electric shock when using or working on electrical equipment. Follow the same precautions you would use without wrist straps, including:

• Make certain that equipment having a grounding type plug is properly grounded.

• Make certain that you are not in contact with grounded objects other than through the ESD Series.”

 
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