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December, 2019
The Dramatic Impact of ESD on the Shop Floor
By Gordon McAlpine, Production Manager, Dynamic EMS
cal short or dielectric breakdown. A buildup of static electricity can be caused by triboelectric charging or by electrostatic induction, which has a dramatic impact on the shop floor. Sometimes these effects are blatantly obvi-
E
ous, like igniting solvents. In other occasions, it can be less obvious, such as dust buildup, coating problems and components jumping out of tape and reel. Then, there can be the scenario of “ESD sales by fear,” where the ESD experts will make you be- lieve that it is even necessary to wear an ESD wrist strap while using a smartphone. Views on ESD go from one extreme to the other.
Keeping on Top of ESD ESD is a concern in the EMS environment,
but in manufacturing it has more to do with the environment than ESD alone. Studies show that low humidity can impact production throughput. This is not surprising when considering the drying effects of low humidity, leading to a possible link between low humidity and ESD. Static electricity is an issue in a variety of en-
vironments. One of the earliest examples of wrist straps was during the Second World War, where op- erators mixing explosive materials were grounded. In the manufacturing environment, the
biggest risk of static charge comes from other peo- ple. To take precautionary steps, machinery should be wired correctly and grounded, as should benches. Manufacturers should consider every person
lectrostatic discharge (ESD) is the sudden flow of electricity between two electrically charged objects caused by contact, an electri-
to be a mobile static electricity generator. Their movement, no matter how slight, will generate static electricity, with walking around the shop floor generating the largest amount. There are mitigating factors that aid or dimin-
ish static charges through dissipation. These in- clude: 1 mW current limiting resistor straps; static
placement nozzles and drying out of solvents, lu- bricants and oils. In electronics manufacturing we can see 0402 chip resistors start to jump out of reel pockets at 35 percent RH. Solder paste viscosity in- creases due to drying out, which also increases the risk of blocked apertures in stencils. It is easy to see the impact of static electricity and humidity on product throughput. Most ESD testing involves specialized equip-
ment, which provides a “pass” or “fail.” Of course, this testing is valuable. However, investigating or even just daily monitoring can be cumbersome, es- pecially in a fast-paced, high-mix, low-volume fa- cility.
If you accept that the largest contributors to
ESD are humidity levels and people, such as a shop floor machine operator, then measuring and recording humidity can be easy. What must be es- tablished is the humidity level in the environment and if it presents an issue.
Measuring with LCDs Dynamic EMS uses LCD displays. These
ESD is a constant hazard in electronics manufacturing, ruining components or igniting flammable solvents.
mats and benches grounded through a resistor; and controlling humidity —relative humidity (RH) levels of 50 percent and above have been found to reduce the risk of static buildup in people. The opposite is true when static levels are lower, with increased dust levels causing blocked
high-impedance components work on very low en- ergy, such as static. The company measures the grounding of machines and benches, board storage ages, wrist straps, and anywhere a person touches or carries a PCB assembly. When a person moves, they build up static
charges. The charge decay and drain is dependent on whether there is a connection (drain source) to ground. In most cases, this drain source is either through wrist straps (when sitting) or heel straps (when walking).
Continued on next page
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