conformal coating PCBs with onboard connectors

[Winfield Hill]

Last year I hand coated the first 15 circuit boards
of my 60-sensor bee-hive monitor, but for the next
15 boards I'd like to use a conformal coating house.
I faced two problems in coating the boards, first,
about 20 pcb-mounting connectors (through-hole, not
that it matters), and second, a host of test points
that I didn't want to seal over.

I solved the first problem with specially-made plugs
and the second with shrouded pins to keep holes dry.
This meant mounting the board with plugs and pins,
spraying, let dry, dismount, and repeat, one board
at a time. Painful and time consuming.

I dunno how to approach the conformal coating house,
will they have magical tricks to solve the problems?


--
Thanks,
- Win

 

[George Herold]

On Thursday, April 25, 2019 at 4:57:51 PM UTC-4, Winfield Hill wrote:

Last year I hand coated the first 15 circuit boards
of my 60-sensor bee-hive monitor, but for the next
15 boards I'd like to use a conformal coating house.
I faced two problems in coating the boards, first,
about 20 pcb-mounting connectors (through-hole, not
that it matters), and second, a host of test points
that I didn't want to seal over.

I solved the first problem with specially-made plugs
and the second with shrouded pins to keep holes dry.
This meant mounting the board with plugs and pins,
spraying, let dry, dismount, and repeat, one board
at a time. Painful and time consuming.

I dunno how to approach the conformal coating house,
will they have magical tricks to solve the problems?


--
Thanks,
- Win

Win, I don't know (so maybe I should just shut up.)
But I'm going to suggest calling/emailing/ some places and
see what they say. If you are doing a small run ~100 or less
then you want to find a small guy who will work with you a bit.
Maybe you can have connectors waxed or covered..
Are you in a hurry? Of course the small guy may cost more.

George H.

 

[whit3rd]

On Thursday, April 25, 2019 at 1:57:51 PM UTC-7, Winfield Hill wrote:

I faced two problems in coating the boards, first,
about 20 pcb-mounting connectors (through-hole, not
that it matters), and second, a host of test points
that I didn't want to seal over.

I dunno how to approach the conformal coating house,
will they have magical tricks to solve the problems?

I'm sure they must have tricks; I've seen conformal coatings on
boards with edge connectors, after all.

One approach I've used, is to get a latex molding compound
(TAP plastics sells it in tubs)<https://www.tapplastics.com/product/mold_making_materials/mold_making_supplies/tap_premium_liquid_latex_rubber/62>

and blob it over the parts you want protected. After it dries, it's easy to
pull off (and it's water-based, most hydrophobic coatings won't attack it).

Another old solution is 'washable solder mask', but that's a ... different kind
of coating.

 

On Friday, 26 April 2019 01:59:42 UTC+1, whit3rd wrote:

On Thursday, April 25, 2019 at 1:57:51 PM UTC-7, Winfield Hill wrote:

I faced two problems in coating the boards, first,
about 20 pcb-mounting connectors (through-hole, not
that it matters), and second, a host of test points
that I didn't want to seal over.

I dunno how to approach the conformal coating house,
will they have magical tricks to solve the problems?

I'm sure they must have tricks; I've seen conformal coatings on
boards with edge connectors, after all.

One approach I've used, is to get a latex molding compound
(TAP plastics sells it in tubs)<https://www.tapplastics.com/product/mold_making_materials/mold_making_supplies/tap_premium_liquid_latex_rubber/62

and blob it over the parts you want protected. After it dries, it's easy to
pull off (and it's water-based, most hydrophobic coatings won't attack it).

We used to use that to keep solder off. Put it on with a nozzled bottle. It just rubs off with fingers after processing.


NT

Another old solution is 'washable solder mask', but that's a ... different kind
of coating.

 

[Mikko OH2HVJ]

Winfield Hill <hill@rowland.harvard.edu> writes:

Last year I hand coated the first 15 circuit boards
of my 60-sensor bee-hive monitor, but for the next
15 boards I'd like to use a conformal coating house.
I faced two problems in coating the boards, first,
about 20 pcb-mounting connectors (through-hole, not
that it matters), and second, a host of test points
that I didn't want to seal over.

The assembly house I use a lot does selective conformal coating.
The machine they're using is Dima HC-200 dispenser, which can
selectively spray the coating and leave holes for test points and
connectors.

--
mikko OH2HVJ

 

tabbypurr@gmail.com wrote in
news:4e605fba-e199-4484-94e8-f7b6a13dc7bb@googlegroups.com:

On Friday, 26 April 2019 01:59:42 UTC+1, whit3rd wrote:
On Thursday, April 25, 2019 at 1:57:51 PM UTC-7, Winfield Hill
wrote:

I faced two problems in coating the boards, first,
about 20 pcb-mounting connectors (through-hole, not
that it matters), and second, a host of test points
that I didn't want to seal over.

I dunno how to approach the conformal coating house,
will they have magical tricks to solve the problems?

I'm sure they must have tricks; I've seen conformal coatings on
boards with edge connectors, after all.

One approach I've used, is to get a latex molding compound
(TAP plastics sells it in
tubs)
https://www.tapplastics.com/product/mold_making_materials/mo
ld_making_supplies/tap_premium_liquid_latex_rubber/62

and blob it over the parts you want protected. After it dries,
it's easy to pull off (and it's water-based, most hydrophobic
coatings won't attack it).

We used to use that to keep solder off. Put it on with a nozzled
bottle. It just rubs off with fingers after processing.


NT

Another old solution is 'washable solder mask', but that's a ...
different kind of coating.

Yeah... That was the pink stuff sometimes powder blue. But we
masked off any through holes or via that were needed downstream of
the wave or reflow step. If the connectors are through hole, then
mask the holes and solder the connectors on by hand after the wave
or reflow, Or douse the whole thing in the mask, cause it peels
right off like you said.

I would worry about small for factor high pin count connectors as
the pink stuff could get under the pins and alter connector function
/ continuity integrity., even if it wipes clean from their surfaces.

 

[Cursitor Doom]

On Fri, 26 Apr 2019 10:09:48 +0300, Mikko OH2HVJ wrote:

The assembly house I use a lot does selective conformal coating. The
machine they're using is Dima HC-200 dispenser, which can selectively
spray the coating and leave holes for test points and connectors.

I just probe through the coating. Today's coatings are invariably self-
healing IME.




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Cursitor Doom <curd@notformail.com> wrote in
news:q9vdus$2u4$4@dont-email.me:

I just probe through the coating. Today's coatings are invariably
self- healing IME.

Absolutely not. Any breech means that water can then invade the very
thing you were sealing against. And no, regardless of how you think
the material 'feels', it does not 'self heal'. Erroneous 'estimation'.

Repair work on coated mil PCB assemblies requires the worked areas be
resealed. So, since they know what they are doing/talking about, I am
pretty sure commercial work follows. If it needed conformal coating to
start with the reason is almost always moisture barrier related.

 

[DemonicTubes]

On Thursday, April 25, 2019 at 2:57:51 PM UTC-6, Winfield Hill wrote:

Last year I hand coated the first 15 circuit boards
of my 60-sensor bee-hive monitor, but for the next
15 boards I'd like to use a conformal coating house.
I faced two problems in coating the boards, first,
about 20 pcb-mounting connectors (through-hole, not
that it matters), and second, a host of test points
that I didn't want to seal over.

I solved the first problem with specially-made plugs
and the second with shrouded pins to keep holes dry.
This meant mounting the board with plugs and pins,
spraying, let dry, dismount, and repeat, one board
at a time. Painful and time consuming.

I dunno how to approach the conformal coating house,
will they have magical tricks to solve the problems?


--
Thanks,
- Win

We use Techspray's WonderMASK (the pink kind). I find it very easy to work with. Goes on easy, comes off easy, does a brilliant job.

https://www.techspray.com/wondermask