Hi Technetters,

Over the years I have been involved in discussions about proper hardware to use when mounting circuit boards and if copper should be part of the stackup even if not a ground point.

I'll bet the answer is "it depends".

At one point we used a screw, split lock washer and a flat washer (labor intensive to assemble), then external tooth SEM screws that chewed up the FR-4. So we added a copper pad to act as a washer. SEM screws still chewed up the copper.  With each of these we occasionally had units returned with loose screws.  Enter nylon patch screws with no lock or flat washers but with a copper pad.  No loose screws.

As time goes on there is someone that states the "standard" configuration uses a lock washer and flat washer and no copper.

I know there are SEM screws that incorporate a lock washer (star or split) with a flat washer, so that eliminates the assembly labor.

We make commercial OEM power supplies, no military stuff.  So what do you use and why?

Phil Nutting  |  HVP Senior Development Engineer   |  Excelitas Technologies Corp

Lab: +1 978.224.4332   |  Office: +1 978.224.4152
35 Congress St, Salem, MA  01970 USA
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