Gluing Down Larger/Heavier Components - Page 1
Forum section: electronics / general

author: meshtron
author_rank: Regular Contributor
timestamp: March 03, 2024, 08:09:50 pm
content: So, I have not had a failure with this yet, but just playing with boards, the two large bulk caps I have "feel" a little less stable to me than I'd like. Picture of board and board in housing below andhere isthe specific capacitor.My parts will frequently be used in a relatively high-vibration environment (think automotive). The housing I design doesn't physically touch the caps (but probably could) - I made that choice because I didn't want the risk of a slight misalignment between board/cap/housing to induce some stress on the joint. So, I'm thinking about gluing these down just for extra insurance against vibration.I am assembling and reflowing these myself, so I have lots of options available (I think). I could put double-sided tape in the top, inside of the housing cavity where the caps live which would stabilize them from the top, but which would make it harder to disassemble the device (which will happen frequently while we're testing/validating but infrequently once we're in production).I could apply some glue, but I'm not sure the right type of glue and process to do so. I would think it would have to be post-reflow, but them I'm just hoping the glue wicks down into the right spot or holds onto the edges. I could also physically add a hole in the board under the cap (but obviously beyond the pads) and glue from the bottom, but again hard to guess how good of a bond I'd get and it seems like glue viscosity would become very important.Or maybe there's a glue I can apply before reflow that wouldn't affect things? That would be nice but seems a tall ask and a good way to cause other fiddly issues.Anyway, looking for something relatively simple to do if such a thing exists. Or, looking for someone to tell me I'm overthinking this and should wait until ACTUAL physical failures occur before I start solving that problem. Thanks all for any input as always!

author: mariush
author_rank: Super Contributor
timestamp: March 03, 2024, 09:11:46 pm
content: It looks like a bit too little solder to me, especially in the area of the potentiometer and the dip switches. edit : on second thought it's probably fine.Anyway, are you against through hole capacitors? You have a 0.1" header on the board, so it's not like the capacitors would be the only ones that are through hole.Your capacitors are also 125c rated, do you really need 125c rating? The estimated lifetime of polymer capacitors is not like with electrolytics where you double the lifetime with every 10 degrees in temperature, it's way more higher lifetime on polymers.Panasonic ZS (4k @125c) is through hole, 10mm and 10.5mm tall :https://www.digikey.com/en/products/detail/panasonic-electronic-components/EEH-AZC1V271B/13574513Rubycon PZS (3k @ 135c) is also through hole , same size :https://www.digikey.com/en/products/detail/rubycon/35PZS270M10X9/15964385With through hole, you could pour a bit of selastic (electronics grade potting compound) around the caps for further rigidity...

author: jc101
author_rank: Frequent Contributor
timestamp: March 03, 2024, 09:22:00 pm
content: I've used some Dow Corning 744 around the base of and between SMD electrolytic caps before, specifically as the environment was high vibration. Added after board testing prior to putting the boards in the enclosure. Never had a failure.Cheaper similar alternatives no doubt exist.https://www.dow.com/en-us/pdp.dowsil-744-rtv-adhesive-sealant.03321916h.html#properties

author: meshtron
author_rank: Regular Contributor
timestamp: March 03, 2024, 09:29:10 pm
content: Quote from: mariush on March 03, 2024, 09:11:46 pmThanks for the thoughts! The headers are there for flashing and testing and I'm using them (almost always) with pogo pins in a fixture I built. So, strong preference to stay away from through-hole for these only because they become the only PTH parts on the board. I'm not morally opposed to hand soldering, but the less hand work I have to do the better.Only reason I used the higher-temp rated caps is that this is a pretty high-current board (up to 20A) and I expected the pours/connection points around the caps to get warmer than what I actually see. Turns out the driver chip (DRV8144S) is where all my heat comes from and most of the rest of the board stays at or below 50C. So, I might be able to find some lower-temp caps when I run out of these.

author: meshtron
author_rank: Regular Contributor
timestamp: March 03, 2024, 09:33:09 pm
content: Quote from: jc101 on March 03, 2024, 09:22:00 pmThat seems quite straightforward! The 48-hour cure time would be a bit of a bummer, but sounds like maybe I could warm them slightly to accelerate that a bit, hopefully enough that I could cure them overnight and fully assemble the next day. Thanks for the tip, I will order some up to play with!EDIT: Aaaaaahhhh! Also seems like 744 also only comes in white. Catastrophic for my stealth motif, but I'll find a workaround

author: jpanhalt
author_rank: Super Contributor
timestamp: March 04, 2024, 12:34:00 am
content: What about a hot-melt glue. Simple, cheap, and used in a lot of import electronics. Easily removed with IPA, if needed. There are lots of options for final physical properties. See: 3M. It can be a difficult company to deal with as a small producer.

author: Mangozac
author_rank: Frequent Contributor
timestamp: March 04, 2024, 12:43:50 am
content: Quote from: meshtron on March 03, 2024, 09:33:09 pmWhy not apply it as the very last step before you assemble into the enclosure? No need to wait for it to cure.I prefer silicone to hot melt glue. Any time I've opened a product that's a few years old that used hot melt glue it has lost its bond.

author: jpanhalt
author_rank: Super Contributor
timestamp: March 04, 2024, 12:49:18 am
content: Not all hot melt is made the same. That's why I mentioned 3M (there are probably other quality producers). Sure, silicone sticks like snot, so does hot-melt snot (credit cr glue). The biggest advantage to hot melt is the ease with which it is completely removed by wicking IPA on it.

author: Smokey
author_rank: Super Contributor
timestamp: March 04, 2024, 01:53:51 am
content: Some Silastic between the caps to mechanically couple them will greatly reduce breakage due to vibration. Essentially turns two 2-Pad devices into one 4-pad device.Ex.

author: Kean
author_rank: Unknown
timestamp: March 04, 2024, 09:44:13 pm
content: Have you considered adding a small piece of adhesive lined EVA foam in the case lid above the caps to put slight pressure on them?Adjust the thickness or density of the foam to match the gap and desired rigidity.

author: thm_w
author_rank: Super Contributor
timestamp: March 04, 2024, 09:53:51 pm
content: Quote from: Kean on March 04, 2024, 09:44:13 pmThis is the easiest if you ever want to take the enclosure apart again. If you don't care about taking it apart can fill the thing with silicone.I do the adhesive foam method to hold lithium cells in.

author: meshtron
author_rank: Regular Contributor
timestamp: March 05, 2024, 08:52:02 pm
content: Yeah, that might be the answer. It would be simple, cheap, and effective.I would want something that still allowed the upper housing to be removed if it had to, but since I'm printing housings out of PETG I bet things will stick much better to the caps than the plastic so pretty low risk of pulling a cap off.

author: tszaboo
author_rank: Super Contributor
timestamp: March 05, 2024, 10:27:52 pm
content: Quote from: meshtron on March 03, 2024, 09:33:09 pmThe 744 is an RTV silicon, which means it vulcanizes at room temperature. After 8 hours or so you can move it, probably even sooner, just don't drop it. It's specifically suggested for electonics.