screw down PCB capacitor mounting solution? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2018, 04:51:16 am
content: So I have a strong dislike of adhesive being used with components on a PCB.As far as mounting options for for PCB capacitors, the only thing I have seen is that the better caps like Sprague sometimes have more pins, I think its mostly for mis insertion protection but I suspect they are more robust.Given the fact that most capacitors like newer SMD ones already have a little plastic base,Would it be reasonable to assume a regular low end cheap 3d printer would have sufficient manufacturing tolerances to produce small brackets that go over capacitors to fasten them to a PCB to match or exceed the protection offered by silastic compound?I thought about doing this by hand before but its quite a lot of parts to make it right out of metal so it looks decent and has a minimal form factor and it seems like a good job for a 3d printer if good filament is used, with the only problem being weakness at high temperatures. I mean without stamping or advanced manufacturing processes,my high end home use idea was to use metal plates with holes in them. So you would have a top roof plate that compresses the capacitors (or multiple caps) with 4 threaded rods (soldered to the top plate) acting as legs, with another metal plate inserted over the rods with holes in it to act like capacitor brackets that would slide over the capacitors and through the threaded rods and be soldered in place at the right height, then have the threaded rods go through the PCB and be attached to the base with nuts from the bottom, this way it could be done without spacers, but the problem would be that you would need to remove the PCB completely to access the capacitors, otherwise if you made spacers you could remove it from the top but then you have alot of small pieces.But this assembly would be very stiff so I am wondering how would it compare to a solution with silastic (which acts as a damper) since its flexible, and if a 'top hat' that is fastened to the PCB with bolts made with a 3d printer could work.You would need to account for the burst disk on the capacitors and make holes on top of any solution btw if you do it so you don't make a bomb.Would you still need some kind of vibration rubber gasket thing between the top of the capacitors, and another one around the perimeter of the fastener? Could it cause unforeseen consequences?My metal scafolding idea would be pretty open so I don't think it would affect the thermal performance too much, but the plastic??

author: helius
author_rank: Super Contributor
timestamp: December 17, 2018, 06:28:26 am
content: If you're willing to use screws, why not use screw-in capacitors with their supplied mounting clamps.

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2018, 06:29:47 am
content: link?\i never saw that system for anything other then monster sizeand not for like polymers and high end onesand their like 20$ minimum, you can do this real cheap if you make the parts to reinforce regular caps.... an example being here:https://www.digikey.com/product-detail/en/cornell-dubilier-electronics-cde/CG801U050R2C/CG801U050R2C-ND/1595578kinda crazy pricing and almost no choice with eSR and other performance specific things, not suitable for normal use, and you still need some kind of base plate under it you need to make yourself, their chassis mount not pcb mount, pcb won't like thatand the electrical connection is screwed so you can't manufacture it easily and offer reinforcement as an option etc

author: Messtechniker
author_rank: Frequent Contributor
timestamp: December 17, 2018, 07:17:31 am
content: Quote from: coppercone2 on December 17, 2018, 04:51:16 amMe too until I found this:Paste Hama 00007091 or Walimex 17368. Conrad has it. You my even find it in some supermarkets in the photography section.It is kneadable, reusable, removable without residues. Photographers use it to hold small items in place. I use it all the time to prevent lightweight objects like scopes from being pushed back or to attach small temperature sensors to a wall, for example. The missus uses it instead of wax to attach candles. Because it does not solidify, it is easily possible to set up the candles strait even after some time.

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2018, 07:52:51 am
content: will that stuff tolerate being at like 60C for 5 years upside down? and i don't know much about moisture etc. Good thing to add to inventory but I still want to know mechanical options.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 17, 2018, 09:20:32 am
content: I've seen nylon furniture, brackets, spacers, etc. used on very tall caps, and maybe on horizontal caps that they wanted to bereallyfancy with.If you're worried about mil-spec quality, then do what mil-spec does. They have the numbers to back it up. Anything said here is just hear-say!But don't go complaining that a $100 metal-case capacitor is too expensive!Tim

author: SeanB
author_rank: Super Contributor
timestamp: December 17, 2018, 09:55:02 am
content: MIL Spec for capacitors is to stick them down with a blob of conformal coat, after using some lacing twine ( or a small tie wrap with stainless steel clip) to hold them to the board. If you have a few in a row then they would mill out a mounting bar for them, either aluminium with a PTFE foam shock absorber, or from engineering nylon and use a through board setscrew and nylock bolt with a washer and insulator both sides. Really high shock loading flexible conformal coat the lot, then hard conformal coat the entire board into a potted block.

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2018, 10:31:57 am
content: Quote from: SeanB on December 17, 2018, 09:55:02 amdo you have a picture of what this looks likecan this still work without the conformal coat or the lacing twine (this is what I am trying to avoid, crazy disassembly procedures).What does this shock absorber look like? How is it configured?

author: coppercone2
author_rank: Super Contributor
timestamp: December 17, 2018, 10:42:36 am
content: Quote from: T3sl4co1l on December 17, 2018, 09:20:32 amhow do I find out what document to look at preferably with pictures and tolerances or do they do all this stuff in order to pass tests with their own in house mechanical development?At most I can think to measure the cap when its cold and when its hot to see how much it expands using a micrometer then I am not sure how to make a bracket for it (are you allowed to squeeze them or should they always be allowed to wiggle a little bit or is this where foam comes in but then how do I find out how hard the foam should be so they don't get squeezed too much?this is alot of weird ass mechanical shitand if you use some kinda foam how do you test how much its squeezing the capacitor because it has its own temperature coefficient.I was just planning on getting a appropriate drill and reamer to make the holding brackets but I don't know about this foam