I agree with Brian Ellis' response later on.

We also build a double sided board which gets conformally coated, so we
assemble shields and other cleanliness restricting items after the board has
been cleaned for all soldering operations.  We're fortunate in that our CC
process is done by an outside vendor who does an additional cleaning/drying
process, but when I worked for a defense contractor, it was verboten to have
anything on the board that restricted the cleaning agent's flow.

Jan Pelchat
Benchmark Electronics

> -----Original Message-----
> From: Steve Abrahamson [SMTP:[log in to unmask]]
> Sent: Wednesday, May 02, 2001 7:01 PM
> To:   [log in to unmask]
> Subject:      [TN] Unusual Cleaning Operation- Help!
>
> Howdy,
>
> I have got a major mess on my hands.  We may soon be running a double
> sided
> SMT product that needs to be fully cleaned due to a conformal coating
> process.
> Both sides of the assembly have two 2" x 1" x .3" RF Shields that are
> soldered to the PCA.  There are SMT components under the shield, and the
> shields have two .040" holes on top- the rest of the shield is sealed.
> Just in case we cannot clean 100% of the residue out of these shields, the
> customer requires a no-clean chemistry solder paste.  (They claim no clean
> residue has caused problems with past due to issues with the battery
> pack...I am not much of an electrical guy, and cannot refute them).
> They are pushing us towards a vapor degrease cleaning method, since they
> had used the process sucessfully during the design phase with good luck.
>
> Question 1: If we did use a non aqueous solvent for cleaning, especially
> one that has evaporative characteristics (any HCFC replacement), could we
> avoid the "bake out" process?
>
> Question 2: Would a cold soak process with somthing like Bioact be a
> viable
> alternative- and be performed without a bake out?
>
> Question 3: Would ultrasonics be valuable (if we had alternating frequency
> such as with the Smartsonic system), or could more damage be done.
>
> Steve Abrahamson
> 208-898-2695
> [log in to unmask]
>
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