Path: ...!weretis.net!feeder8.news.weretis.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: John Robertson Newsgroups: sci.electronics.design Subject: Re: How to protect circuit boards that must be exposed to weather? Date: Wed, 7 Aug 2024 14:34:14 -0700 Organization: A noiseless patient Spider Lines: 88 Message-ID: References: <1rxsO.16610$yI05.8707@fx38.iad> Reply-To: spam@flippers.com MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Wed, 07 Aug 2024 23:34:17 +0200 (CEST) Injection-Info: dont-email.me; posting-host="635856a27b82b5343efa4d15f32f832b"; logging-data="3563747"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX19pbMyMOUU6gVG+DtcfTFZK7+eDVqzV5+o=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:twc6EcTnndMNSGz0fMwwKK8t5/Y= Content-Language: en-US, en-CA In-Reply-To: <1rxsO.16610$yI05.8707@fx38.iad> Bytes: 4497 On 2024-08-06 3:27 p.m., Glen Walpert wrote: > On Thu, 1 Aug 2024 17:50:29 -0700, John Robertson wrote: > >> I have another problem - display panels on an outdoor hammer game - the >> style that you swing a hammer at a pedestal and it lights up a column of >> LED panels with 8x8 graphics. >> >> The one I am repairing was made in 2001 and it is breaking down. The >> surface mounted serial drivers are loosing connection to the PCBs from >> being thermally stressed over a couple of decades of outdoor use and I >> want to make replacement panels (the original company has abandoned the >> product) that will be more durable. >> >> Currently on the rear (somewhat protected) side of the board is the >> electronics, covered (or course) with a conformal coating. The outer >> side is an 8 X 8 matrix of LEDs in groups of 8 for each pixel of the 64 >> pixels on the panel. >> >> There are 40 - 8 x 8.75 inch panels going up around 30 feet... >> >> Is there a better way to solder on SMD devices to help avoid thermal >> solder failure? After connection corrosion, the biggest problem is >> solder failure of the SMD pads to the PCBs. >> >> Thanks! >> >> John :-#)# > > If the column of lights is attached to the same base as the hammer target, > there could be significant solder fatigue from the vibrations traveling up > the light column. No, the tower is on its own, no risk of shock at least! > > Switching to lead-free will improve fatigue resistance. While there are > lead-free alloys specifically designed for good fatigue resistance, and > any solder mfgr app engineer could make a recommendation, the standard > SAC305 is a significant improvement over tin-lead according to numerous > test results published in the industry trade magazines like SMT > Technology. Thanks for that information! > > Stiffening the boards with a thicker material or with stiffeners will > reduce thermal bowing from sunshine. Leaving all unused area covered with > copper ground plane and white or light colored soldermask might help. Copper ground plane is planned. > > Flexible mounting to isolate vibration might help, perhaps clamp between > silicone foam strips with rubber bushings around the screws or similar, > could also provide sealing of the back side. It is not so much vibration as much as thermal changes over a day in the sun...times many days! > > Flexible conformal coating will prevent the coating from stressing solder, > as can happen with rigid materials due to differential thermal expansion. Conformal coating is part of the problem for repairs. While it is flexible it doesn't peel off easily at all - which I guess is the intent - but this does make it harder to repair. Are there conformal coating that respond well to a solvent that isn't toxic? > > As Buzz mentioned, underfill can help if your assembler has the > capability. I will look into that too. > > Regards, > Glen Thanks for taking the time! John :-#)# -- (Please post followups or tech inquiries to the USENET newsgroup) John's Jukes Ltd. #7 - 3979 Marine Way, Burnaby, BC, Canada V5J 5E3 (604)872-5757 (Pinballs, Jukes, Video Games) www.flippers.com "Old pinballers never die, they just flip out."