About the soldermask

This is one of the main reasons for solder mask over bare copper (SMOBC)

soldermask is not flexible enough to not crack and peel when the solder underneath it reaches the
melting point.  I have been involved in bare PCB manufacture for over 12 years, and do not know
of an additive.  SMOBC is the way to go.

About warp and twist.  The percentage noted is the % of the longest dim of the PCB.  5% of a 10
inc long pcb is .050".  The quickest way I know of to measure the warp of a pcb is to lay the PCB
flat, with the bow up.  then a .050 pin gauge can be rolled under the bow.  If it fits, the bow
and twist is greater than spec.

David Ciufo
DC Circuit Design  Inc.
[log in to unmask]


mdsn500 wrote:

> We had some boards in with LARGE areas of tin/lead, unmelted, with
> soldermask applied to them. This lot had peeling of the mask from the
> unmelted(PrimarySide) as well as secondary side. What are some specific
> additives that can be called out to help this problem?
> Also, how is Bow and Twist measured? What does the percentage indicate?
> Would appreciate any help. Thanks everyone-
>
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