Rich,

I have several questions.

1. How long were the products in the field?

2. How much time did the "fielded" products spend in conditions of > 60%
humidity?

3. What form was the copper compound found in the coating (oxides,
salts, combinations, ect...)?

4. Are you coating over "no-clean" flux ?

5. Where these boards "reworked" prior to coating?

1-2577 coating is formulated not to form acids during the cure cycle. It
generates alcohol (which can
desolve certain materials).

David A. Douthit
Manager
LoCan LLC



Rich Lasko wrote:

>Good morning all,
>
>
>
>I have a customer who is having problems with a couple of their
>assemblies.  It appears that the conformal coating (Dow Corning 1-2577)
>is reacting with the untinned copper portions of an IC (MC68HC908AZ60A).
>The untinned portion is on the sides of the lead right near where the
>lead enters the package body.  It seems that the copper is leaching out
>into the conformal coating and lowers the resistance between the two
>pins.  (When the two pins are measured they read approx. 80K ohms - 150K
>ohms).  Without the conformal coating the resistance is much higher (>
>1M).  This lower resistance is causing some erratic failures from time
>to time.  When my customer sliced through the conformal coating between
>the pins with an exacto knife the resistance returned to a more normal
>reading and the unit worked fine.  They have sent this unit to a lab and
>the lab report stated that they found traces of copper in the conformal
>coating.  So my questions are as follows:
>
>
>
>1.)     Is it common to have untinned portions of a SMT IC such as the
>one identified above?  Or should the lead be completing tinned?
>
>2.)     Has anyone else seen this type of problem with copper in the
>conformal coating?  If so, what did you do about it?
>
>3.)     Is there a concern from a solder paste position and how the flux
>in the paste reacts with the copper and then is ultimately conformal
>coated in a later process?  (This question applies to both an aqueous
>SMT process and a no-clean SMT process)
>
>
>
>Need a little help and insight here.
>
>
>
>Thanks!
>
>
>
>Rich Lasko
>
>
>
>
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