Dear Matthew:
I need some more information regarding your process before commenting.
Am I to understand the gold tabs are nickel/gold plated; then LPI
applied, imaged, and developed? Also, could you give me a physical
description of the stain, a description of your developing process
including bath strength, and method of control, type of developing
solution, and post rinsing procedure including water quality (soft, DI
or hard water, etc.). Is the stain exacerbated during curing? Is there
a higher propensity for staining when the bath is new, or toward the end
of it's life?
Regards,
Ted Stern
612-479-6525
Matthew Byrne wrote:
>
> Has anyone every had experience developing solder mask on gold plated
> boards? We get the impression that the mask has an affinity for the
> gold. It leaves stains that are very hard to remove. We see them
> after developing, & are looking for a method to remove them before
> curing.
>
> Matt Byrne
> HADCO-Owego
>
> ______________________________ Reply Separator _________________________________
> Subject: Re: [TN] Soldermask developing
> Author: "TechNet E-Mail Forum." <[log in to unmask]>, [log in to unmask] at
> SMTPLINK-HADCO
> Date: 2/9/98 12:50 AM
>
> With standard sodium or potassium carbonate developing solutions (generally
> 0.9 to 1.1%), feed and bleed systems for LPI solder masks are maintained at a
> pH level of 10.7 to 10.8. Since the initial makeup of the developing solution
> in the holding tank with DI water is in the range of 11.0-11.2 pH, the system
> is fairly easy to control by feeding directly into the developing sump. A
> number of companies make feed and bleed systems for controlling developing
> solutions. The feed rate is usually controlled by pH of the solution in the
> sump.
>
> These days, a number of companies (Surfact-Tek, Morton, Dexter, etc.) offer
> "doped" developing solution concentrates that are designed for the liquid,
> photoimageable (LPI) solder masks. These concentrates contain amounts of
> sodium or potassium hydroxide that increase the pH of the operating solution
> in the sump (up to 12.0 pH), increase the loading capacity of the developing
> solution and allow for better development of the solder mask out of the holes
> (important if screening is used to apply the mask).
>
> Whichever way you go, I'm sure you will have success with using the feed and
> bleed method to control your developing with your LPI solder mask.
>
> Hope this helps.
>
> Larry Fisher
> Dexter Electronic Materials
> [log in to unmask]
>
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