There are many possible causes for solder mask lifting at wave solder.
The most common causes are surface prep before solder mask
application and final cure of the solder mask. Something you can try is an
oven bake, at cure temp (normally 300F), before you begin assembly. Try
30 to 60 min dwell time.  This will serve two purposes:
1. Help insure proper cure of the solder mask
2. Drive out moisture that may have been picked up by the mask or the
base laminate.

Be careful to not over bake the solder mask as this will cause some
solder masks to become brittle. Check with your supplier to find out what
the masks you are receiving can withstand.

You didn't mention if the flaking was over the laminate or over
conductors. This could help pinpoint the cause.

As far as testing incoming boards to IPC SM 840C, it would be impossible
to test to all of 840's requirements. Some of the tests take a month to
complete. 

Hope the info helps,

Bob Metcalf
Morton Electronic Materials
714-730-8356

>>> Jon_Silvernail <[log in to unmask]> 07/26/96 08:03am >>>
     
     We are looking for solutions for the random occurrences of the solder

     mask flaking.  We are experiencing the flaking from several board 
     manufacturers and several different masks, LPI and Dry Film.  The 
     flaking is occurring during the wave solder process.  
     
     We use a no-clean flux and spray fluxer.  We  run at 4.5 ft/min., with 
     a top side temperature at 210F, with five feet of bottom side IR 
     preheat and 2 feet top side.  Our incoming inspection does not test to 
     IPC840C, does anyone? 
     
     Thank you,
     
     Jon Silvernail
     [log in to unmask]
     

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