In a message dated 11/20/2000 10:26:32 PM US Eastern Standard Time,
[log in to unmask] writes:

> We have a bunch of boards where after wave soldering the solder mask is
> wrinkled.

Obviously "aged" boards.  Oh stop, yer killin' me............

>  We have quaratined the remaining bare PCB's but really need to use the
ones
> that are wrinkled.

Are the boards, by chance, solder mask over a melting metal, such as
tin-lead?  Are they wrinkled on both sides of the board or one side only?
Are they SMT boards, thru-hole, or mixed technology?  Are we talking a $10
board or a $1500 board?  What is the end  use environment  or application?

>  We have performed the IPC test using adhesive tape and the mask does peel
> off.

Not surprising.  A wrinkled mask means you have loss of adhesion to the
substrate.  This comes from either the substrate moving and expanding and the
mask to rigid to keep up (e.g. solder mask over melting metal), or a problem
with the mask processing, or pre-mask cleanliness problems.

>  My question to the technet guru's is,  What can we do to these boards so
> that we can use them?

The decision on whether to use them or not depends on what the cause of the
problem is.  If the problem was solder mask over melting metal, shoot the
people that were responsible and move on.  You can probably still use the
boards but be prepared to do lots of de-bridging and lots of inspection.  The
bottom line is what your customer will accept.

If the cause of the problem is poor mask cure, then some baking may complete
the mask cure, at least enough to use.

If the cause of the problem is poor pre-mask cleanliness, then either scrap
the boards or strip the mask and have it re-applied.  Ionic or organic
contamination threatens the reliability and function of your final product.
No amount of conformal coating will stop this problem.

>  We varnish coat all the boards- will this provide enough protection, what
> about if we double coat them?

Double coating would give you more problems than it would solve.  When you
say varnish, do you really mean varnish?  I was applying some to some nice
oak cabinets I made just last night, but I wouldn't apply the same material
to electronics.  Hmm Minwax as a competitor to Humiseal.......  Where was I?
If you meant conformal coating, then you might consider a coating that has a
different moisture permeability.  Acrylic has the most, epoxy the least.
Again, what will your customer accept?

For what it is worth.

Doug Pauls
Technical Director
CSL

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