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Need an ESD Guru

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Need an ESD Guru | 17 October, 2006

I'm in the middle of developing an ESD program at my company, trying to adhere to S20.20 as much as possible (and the suggestions of the ESD audit conducted before I got here).

I've been discussing the pros/cons of pink-poly foams and black foams. Both items are currently being used, and, as far as my rusty memory goes, this needs to change. I am, however, having some difficulty in explaining this to my boss, as I can't remember the details.

As I recall, pink-poly bags and foams etc are generally anti-static, that is...they resist the generation of static electricity. While the black foams and carbon impregnated bags are conductive/static-dissipative.

As I also recall, conductive/dissipative is better than anti-static. However, I'm having trouble articulating exactly why this is the case. Anyone have any advice for making this argument?

As a side note, we're also discussing the need for ground mats in the work area. Obviously benches that are being regularly used need ESD mats, but one argument that I'm losing is that if we're assembling boards on ESD safe foams, and transporting them on ESD safe trays/racks, why do I need an ESD mat on the benches. Assuming that the boards are not removed from their foams/transports onto the benches.

Thanks for any help/advice.


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Need an ESD Guru | 17 October, 2006

It all has to do with charges being drained. IIRC the pink stuff won't build up a charge but doesn't drain it well. As for the need for mats, how are charges being drained now? I don't think you can have no charges building up.

With ESD all you can do is all you can do. No system will prevent all ESD damage, all you can do is minimize it.

A sales guy told me he went to a place that said they didn't have an ESD problem. He asked why their rework area was bigger than their production area.

I worked at one place that got new owners sometime after I had left that implemented ESD practices. The repair people were looking for the failed boards to fix but their simply wasn't as many.

What is your fall out rate?

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Need an ESD Guru | 17 October, 2006

In the past, black poly was used as a bridge between pink poly and shield bags because of slightly lower cost and offering some shielding as opposed to none with pink poly. However, as the price of shield bags continue to drop the usage of black poly will likely drop as well. Because black poly bags are opaque, the bag's contents must be removed for identification. This creates a new opportunity for static damage.

ESD Protection Links *



ESD materials classification Conductive materials: * Surface resistance (IEC 61340-2-3)10^2< Rs< 10^5 ohm * Volume resistivity (ESD STM 11.12) Pv< 10^5 ohm-m. Dissipative materials (typical EPA-area materials): *Surface resistance (IEC 61340-5-1)10^6 < Rs< 10^9 ohm Low-Charging materials (Antistatic): * Surface resistance (IEC 61340-5-1)10^9 < Rs< 10^11 ohm * Static decay < 10 s (RH 12%) and < 2s (RH 50%) ESD-Shielding materials: * Discharge shielding (ESD STM 11.13)Energy E < 50 nJ Note! All values must pass in RH 12% and RH50%, Temp. 23*C conditions.

Resources for developing an ESD Control Program: * EIA-625, Requirements for Handling Electrostatic-Discharge-Sensitive Devices (ESDS) * Appendix K of Mil Handbook 263B - ESD damage prevention checklist * MIL-STD-1686C, ESD Control Program [Electrostatic discharge control program for protection of electrostatic parts, assemblies and equipment.] * ESD Association Advisory, ESD ADV-2.0-1994 --Overview of ESD fundamental guidelines from effective control of electrostatic caused problems. --Discusses the causes of ESD and the different types of device failure. --Material electrical characteristics --Device sensitivity: How much static protection is needed --Chapters on: ---Points of control ---Implementing an ESD control program ---Audits and checklists ---Symbols ---Device testing * ESD Program Management: A Realistic Approach to Continuous Measurable Improvement in Static Control; Dangelmayer, T; Kluwer Academic Pub 1999 e2; 0412136716

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