Vibration protection for SIP-3  1A DCDC isolated reg in automotive - Page 1
Forum section: electronics / projects

author: Psi
author_rank: Super Contributor
timestamp: April 30, 2022, 11:54:21 pm
content: I have a general automotive product (not life-critical) which has those small 3pin SIP DCDC regs.See picture below for what I mean.On the PCB this part is by far the one most likely to be affected by vibration. (Since it's TH and anchored by 3 pins in a single row and they are slightly offset to one side of the part).So I want to add some vibration protection/mitigation to this part when I populate it on the PCB.Two things have occurred to me- Some sort of silicone rubber glue added under/around the parts. (Salastic? I dunno how that word is supposed to be spelled.)- Some sort of rubber pad, like you would use behind a TO220 for isolation, between the DCDC module and the PCB to provide some damping.Does anyone have any better ideas?(Changing to a new part is not an option for this first batch, though I may try to source the SMT version in the future as it has alternating pads out each side instead of only down one side, so is probably more immune to vibrations)

author: Someone
author_rank: Super Contributor
timestamp: May 01, 2022, 12:34:38 am
content: Quote from: Psi on April 30, 2022, 11:54:21 pmSilasticTM

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 01, 2022, 12:37:42 am
content: Quote from: Psi on April 30, 2022, 11:54:21 pmThe generic term is electronics safe RTV. Note that regular RTV is acidic and may cause reliability issues in the long run.

author: Psi
author_rank: Super Contributor
timestamp: May 01, 2022, 12:38:48 am
content: Is Silastic a good option for this sort of part?I'm thinking it might be better to epoxy it on so it's rigid, rather than adding some silicone rubber?Obviously if the part is huge you cant epoxy it because it may crack the epoxy under its own weight when hit by a large vibration. But a 3-SIP module is quite small and not that heavy.

author: nctnico
author_rank: Super Contributor
timestamp: May 01, 2022, 12:39:31 am
content: Gleuing those modules down to the board could be a good idea. Where is this board mounted? If it is not directly on the engine, I wouldn't botter. But maybe test first using vibration table; the legs aren't that long so have little room to flex. If the board is double sided then the solder joint will end right at the housing. It probably is a good idea to keep a bit more distance in the thermal relief so the pad heat ups entirely allowing the tin to fill the entire hole.

author: Psi
author_rank: Super Contributor
timestamp: May 05, 2022, 10:54:06 am
content: Quote from: nctnico on May 01, 2022, 12:39:31 amIt's on a trailer, so the vibrations will be more of a bouncing up/down when driving down the highway.

author: max_torque
author_rank: Super Contributor
timestamp: May 05, 2022, 08:59:23 pm
content: If you can still change the pcb design, simply put through plain through holes of say 3mm diameter immediately either side of the part and secure with a zip tie over the part and round the back of the pcb through those two holes that pulls the dcdc housing hard to the pcb itself!

author: Psi
author_rank: Super Contributor
timestamp: May 05, 2022, 10:47:55 pm
content: Quote from: max_torque on May 05, 2022, 08:59:23 pmThat's a great idea for the next PCB run. Thanks.This current PCB run is already done (but regs not yet soldered to pcb). So i'm just trying to figure out best method to attach them.It's basically a choice between hard glue like epoxy or soft glue like silicone

author: TimNJ
author_rank: Super Contributor
timestamp: May 06, 2022, 03:08:07 am
content: In my experience, you want a relatively stiff variety of RTV silicone.Household RTV silicone from the hardware store is cheap and plentiful *but* it is generally pretty soft, and in my experience, too soft to properly support electronics components. Granted, this tiny little SIP regulator has very little mass, so it would probably be fine. (If you do go this route, just make sure to use a variety which does not produce acetic acid as it cures as this has some potential to corrode conductors.)The silicone RTV used on the assembly line at my work (well at our factory) is pretty tough when it cures. In terms of "toughness", it's somewhere in between hardware store RTV and a rubber car tire.You can also consider a thick adhesive. Most common epoxies are acrylic based. These generally cure glass hard and very strong, but will brittle fracture if stressed too much. Instead, you can try a urethane adhesive, which is still much harder than RTV silicone, but still has some compliance to it.I've used something called Parson PARBOND 905 off McMaster and it was a nice material - very strong, but you can still put a little dent in it it if you poke it with a pick or similar.https://www.mcmaster.com/7448A22/