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How Serious is Static Electricity?
seanadams.com asks: "My company is considering the purchase of a small surface-mount assembly line so we can do our manufacturing in-house, and the issue of static control has come up. We've all been told to take ESD precautions when handling electronics, but how much precaution is enough? Obviously we plan to do the easy stuff like making sure that equipment and work surfaces are properly grounded. However, many shops go even further - conductive shoe straps, wrist staps, special flooring, humidity control, etc. The SMT equipment vendor says that it's unnecessary, and I would tend to agree. I've handled tons of electronics over the years and have never been able to attribute a single failure to ESD damage. Granted, Silicon Valley is a fairly humid area so that may be a contributing factor. Has the ESD threat been blown way of proportion by the guys who sell those little grey bags?"
Basically, you don't have problems with static when your only dealing with a small sample, but increase the sample size, you are increasing your chances of causing damages to something within that sample. So, for a manufacturing operation, I'd say it is worth it.
Perform a benefits/loss analysis. If you handle extremely expensive equipment that can't be damaged, then maybe it would be wise to invest a little more into ESD protection. On the otherhand, if you're manufacturing small boards with little value, then don't invest in ESD protection. You said it yourself, that you have NO cases of ESD damaging electronics as long as you've been there. If one part per million gets damaged and it doesn't cost much to replace, then forget about ESD protection.
Just because you can't immediately establish a cause and effect with ESD, doesn't mean it's not causing damage. ESD can happen without you even noticing and it's especially hard to detect if it doesn't cause a failure outright. I.e. if a discharge doesn't outright kill a product, it can still do damage that increases the likelyhood of failure further on in the life of the product, or even worse, variability. Far worse than a product that you know doesn't work, is one that appears to work but produces wrong or variable output. Combined with the sheer number of products that have the potential to be damaged, increasing your ESD defence will likely give a decent increase your product's overall reliability.
If your product is so cheap that you don't care about failure and just want to produce as many of them as cheaply as possible, then go ahead and skimp on ESD. Just make sure you have a good system to deal with the failing products that will cost you less than the increased ESD defence.
Here is a link. Sorry, all I could find is an Angelfire site. I originally read about it in this book, I think.
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