Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

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SMT electronics assembly manufacturing forum.


Liquid, Dispensable Solder Mask

Shane Lay

#4621

Liquid, Dispensable Solder Mask | 20 March, 2000

We are planning on converting to a no-clean soldering chemistry and will need to replace our water soluble liquid solder mask as a result. Does anyone know of a dispensable, "peelable" solder mask I can evaluate? It would be nice to find one that is automatically dispensable by Camalot and Asymtek automated liquid dispensing machines. I would think that all the leading soldermasks would fall within the typical bottomside adhesive cure profiles so I'm focusing first on a good dispensable mask. Thanks in advance!!

Shane

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#4622

Re: Liquid, Dispensable Solder Mask | 21 March, 2000

Shane: We don�t dispense, but we have thought about it. Several points about peelable solder masks in a no-clean (low residue) process:

� Beware of latex peelable solder mask with a low res process without extensive testing. The problem is usually the cure reaction and what out-gasses from the mask during the curing. The good part about that is that you can do the evaluation of the solder mask, while you compare fluxes with your board finishes. � Some peelable solder masks are laced w/ammonium hydroxide and are real SIR killers. This should be a big time concern for low res people. � Natural latex, low ammonia, types were less conducive than higher ammonia content types, but still produce corrosion. The variable in the process seems to be mask thickness. The mask should be applied in as thin a layer as possible. Thick mask must trap ammonia under the mask. Baking a thick layer of the mask seems to make the problem worse, because the mask skins over, the board and protected land pattern are basked in ammonia and corrosion results. (Doesn�t sound like dispensing to me, does it?) � Check your assumption about curing processes as you move through the product evaluation. UV, humidity (light air), and heat cures could be part of your evaluation matrix. � Consider the ability of the mask to "stand-up" under solder heat cycles. Some peelables get crusty after their first cycle.

Good luck Dave F

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Shane Lay

#4623

Re: Liquid, Dispensable Solder Mask | 23 March, 2000

Dave, Thank you for the information. We will be conducting several tests in the near future that will evaluate the corrosion/contamination response as it is our primary concern once we remove our aqueous processes. We are well aware of the effects of outgassing during cure processes. We have had to make changes to our SMA chemistry and cure profiles as a result of voiding and flux entrapment. In your experience, have you found a liquid soldermask that is most compatitable to a no-clean process? Thanks.

Shane

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#4624

Re: Liquid, Dispensable Solder Mask | 23 March, 2000

Sorry, we run a WS shop that doesn't have enough margin to affort to use no-clean. Good luck. Dave F

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