Re-working PCBs.....cannot program microcontroller on PCB due to conformal coating

[treez]

Hello,

We order PCBs with LED drivers on them, and also microcontrollers on them too.

We have just ordered 500 PCBs, and we specified that the PCB factory should populate the PCBs, and conformal coat them.


....We were going to program the microcontrollers on these PCBs with our Pikkit3 which we have on the production floor.....however, the conformal coating has got into the plated through holes of the programming pads and the programmer cannot program the microcontroller.

So we need to remove the conformal coating from inside these 1.2mm diameter PTH's, then solder in 5way pin headers (Farnell 9731105)

5way programming headers:
https://uk.farnell.com/molex/22-03-2051/header-square-pin-0-1-5way/dp/9731105?Ntt=9731105

....we then need to solder in the above pin headers, then program the microcontroller.....then de-solder this 5way pin header, then conformal coat over the PTH's again so that the whole board is still conformally coated.



....The problem is, at the moment we are removing the conformal coating from inside the PTH's by prodding down them with a jewellery screwdriver, and it is taking ages......we really need some solvent to remove the conformal coating , but do not know of one, ...do you know of a solvent for this?

We must remove the 5way pin headers after programming because the conformal coating will not coat over the needle-like pins of the pin header.

The conformal coating is needed because the enclosure may well let in moisture which would otherwise cause shorts on the PCB.

 

[betwixt]

You can solder through most conformal coatings. It doesn't smell very nice so use an extractor fan but the heat of a soldering iron should be enough to break the coating down and allow solder to flow.

If you need a solvent, "ULS" (Ultrasolv) will remove it and you can use "HPA" to re-coat it afterwards. Both are made by Electrolube.

For future designs, just use pads, don't drill and plate them. You can easily connect the programmer to the pads with spring loaded probes and receptacles:
example: https://uk.farnell.com/feinmetall/f10007s150l200/probe-spring-contact/dp/2009282
You may have to make a holder to mount the receptacles in-line but it's simple and you can use it over and over again.

Brian.