I am curious what methods are most suitable for securing PCBs. I have a large PCB which is fixed to a sheet metal enclosure using #4-40 x 1/4" stainless steel screws. The receiving end is a #4-40 captive standoff (PEM product). Initially I was not doing anything to prevent the screws from vibrating out. Sure enough, I started getting complaints that the screws were backing out just during shipping alone. So, I started to use a loc-tite product. This works well, but it's very labor intensive to put a drop on each screw. I have not used a lock washer as it tears up the PCB. Any suggestions?
Securing PCBs – Screws Vibrating Out
mechanicalpcb
Related Solutions
It's not about wire size and trace width. Those are dictated by the current no differently than for low voltage lines. The issues is insulation and spacing.
To be safe, leave 5mm creapage distance between anything line-connected and everything else. There are various standards, but if you can keep to 5mm spacing, you're pretty much covered.
I can hear Russell already typing in New Zealand warning you in capital letters and italics how dangerous anything connected to the line is. Yeah, yeah, he's right but I'm figuring you know not to stick your finger in a light socket and put the other hand on the kitchen faucet. Besides, if you want to kill yourself that's your business. That's why we keep a supply of Darwin awards around.
There's a lot more to this, but I gotta now. Just remember, 5mm and don't touch the kitchen sink.
No problem. I had to look for a picture that illustrates the technique:
You make a PCB with plated through holes on the PLCC's pads, so at a 1.27 mm pitch, and mill the four sides so that you get the half holes like in the picture. These are easily solderable on the old PLCC footprint, it's an often used technique, called castellation.
A picture of a complete board:
and another one:
or this one from a question posted 1 minute ago:
You get the idea.
You'll have to find a part which fits inside this small PCB, but given the miniaturization of the last years that may not be a problem.
edit 2012-07-15
QuestionMan suggested to make the PCB a bit larger so that the PLCC's solder pads are under it. For BGAs the solder balls are also under the IC, but that's solid solder balls, not paste, and I don't know how solder paste will behave when squeezed between two PCBs. But today I bumped into this IC package:
It's the "Staggered Dual-row MicroLeadFrame® Package (MLF)" of the ATMega8HVD, and it has pins under the IC as well. This is 3.5 mm x 6.5 mm, and weighs a lot less than the small PCB. That may be important, because thanks to the low weight capillary forces of the molten solder paste can pull the IC to its exact position. I'm not sure if that will also be the case for that PCB, and then positioning may be a problem.
Best Answer
Crinkle washers (aka wavy washers) do the same job as shakeproof/star washers and don't damage the PCB. They can also be removed and re-tightened more often than star washers without degradation.