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 <jrr@flippers.com>
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: <v90p8p$3co73$1@dont-email.me>
References: <v8hagn$2f8eq$1@dont-email.me> <1rxsO.16610$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."