How to protect circuit boards that must be exposed to weather?

It might be worth using 3528 automotive LEDs. These have a leadframe which gives some mechanical compliance. Also, make the SM pads larger than usual to get more solder into the joint.

John

Underfill

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.

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.

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.

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.

Flexible conformal coating will prevent the coating from stressing solder, as can happen with rigid materials due to differential thermal expansion.

As Buzz mentioned, underfill can help if your assembler has the capability.

Regards, Glen

No, the tower is on its own, no risk of shock at least!

Thanks for that information!

Copper ground plane is planned.

It is not so much vibration as much as thermal changes over a day in the sun...times many days!

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?

I will look into that too.

Thanks for taking the time!

John :-#)#

You can solder right through acrylic conformal coating.

Cheers

Phil Hobbs

Board stiffeners to reduce warping, compliant mounting to allow thermal expansion without restraint, and cooling with a fan blowing up the column should all help some with that.

The non-toxic part is the issue there. Miller-Stephenson sells a conformal coat stripper which will remove all coatings except epoxy which they claim is environmentally friendly but I haven't used it or read the MSDS:

Underfill is generally epoxy, glues the components to the board, great for shock and vibration but terrible for rework.

Drat, I didn't think of that as a problem. These panels are currently screwed (4 screws on each of two sides) to an aluminum column...it makes sense that the column expands with temperature changes and if the boards are secured tightly (8 screws/panel) then this could be part of the issue. Flexible mounting needs looking into!

I'll take a look into that.

I think with new panels that securing the chips to the board with underfill might well be a good idea.

Thanks!

John :-#)#