Gents,

 

We have gotten some boards in house in which the soldermask is failing.

 

SYMPTOMS:

o LPI solder mask bubbles off of copper.  Looks a lot like SMO Tin Lead, but it is really SMOBC

 

o 98% of the time it happens at a soldermask edge.  That is to say at the edge of a via, at a score or route, etc, where the soldermask stops.

 

o 98% of the time is occurs in a large area of copper.  That is to say that if we use copper on an outer layer as a shield or a thermal heat sink, and this large copper area has some untented vias in it, that is where the failure will be.

 

o Symptoms appear after wave solder. 

 

o Happened on several board designs from a single supplier. 

 

o Sent PCB's out for analysis to several places who found no inherent issue with the bare PCB's.  Mask adhesion was good.  No contamination.

 

o We repeat the problem in all of our factories.  Supplier says they are not seeing this at other customers.

 

o Process improvement activities at the supplier seem to indicate that more attention to scrubbing, drying, and then getting the soldermask on in a timely manner has improved the situation, but we wish to identify root cause and be sure we kill the beast.

 

Comments?  Anyone live through this before?

 

 

 

 

Thanks,

 

Lang
x5046