Norm,
     
        Are you absolutely sure they were HASL and not selective solder
     strip. If they were the latter, then it sounds like the "backprinting"
     of the QFP areas had some solution sepage that attacked the edges of 
     the SMT pads.
     
     Groovy
______________________________ Reply Separator _________________________________
Subject: FW: ASSY: Fine Pitch Dewetting?
Author:  [log in to unmask] at SMTPLINK-HADCO
Date:    4/26/96 1:39 PM


     
Rudy,
     Because it was confined to the fine pitch areas, there may be a 
connection to residues but if the problem was solder mask residues, wouldn't 
the result be "non-wetting" with some visible areas of exposed copper?
     These boards were HASL'd by the supplier and they looked just fine. 
 After they went through our IR process, some of the fine pitch pads do not 
stay fully wet with solder.  No exposed copper can be seen, but on some of 
the finished solder connections ~20 - 30% of the pad surface refuses to 
allow the new solder to flow onto it.  Generally these areas are from the 
outside of the pads inward.  None were in the middle of the pad.
      At this point, I'm open to suggestions.
     
           Norm Dill
           [log in to unmask]
 ----------
From: TechNet-request
To: TechNet
Subject: Re: ASSY: Fine Pitch Dewetting? 
Date: Thursday, April 25, 1996 11:19AM
     
Is it possible that the problem is coming from soldermask residues that the 
developer did not remove??  This would account for it not occuring in large 
pad areas, as the developer may have trouble getting into the very small 
areas.
     
Rudy Sedlak
RD Chemical
     
 ----------------------------- Original Post --------------------
     Recently we have seen dewetting (~20 to 30%) that appears only on some
of the fine pitch pads.  Larger pads with various components on the same 
boards are ok.  This has been seen on HASL boards from two different 
suppliers.  There have been no reports of problems with our regular daily 
production lots.
     Any opinions would be welcomed.