Dave-
     
     Could you provide the author name and/or publisher for "The Mechanics 
     of Solder Alloy Wetting and Spreading", ISBN 0-442-01752-9?
     
     Thanks
     
     Michael S. Alderete
     email: [log in to unmask]
     


______________________________ Reply Separator _________________________________
Subject: Re: PCB board age
Author:  [log in to unmask] at _internetcc
Date:    9/17/96 11:11 AM


     Good Morning Tom-
     
     I don't know of any specification requirements that would restrict you 
     from using a reflowed pwb but why were the pwbs reflowed after 9 
     months of storage? Any reflow operation will increase the amount of 
     copper/tin intermetallic you have on the pwb. If the fusible solder 
     layer isn't thick enough then you will have the copper/tin 
     intermetallic "grow" to the surface and become oxidized. At that point 
     you can either use a stick of dynamite or an acid flux to make things 
     solderable again! Take a look at figure 6-2, page 162 of "The 
     Mechanics of Solder Alloy Wetting and Spreading", ISBN 0-442-01752-9, 
     for a nice depiction of how the amount of fusible solder available can 
     impact your solderability. I have seen people "reflow" poor solderable 
     pwbs in the past as a method of restoring the solderability but this 
     is only effective if the source of the solderability degradation was 
     heavy surface oxidation. If the source was intermetallic oxidation 
     then the reflowing only makes the pwb worst. This is also the reason 
     many assemblies process HASL fabricated pwbs in short times (6-8 
     months) - the HASL process tends to leave a thinner solder coating 
     than other fusing processes and can be more susceptible to 
     intermetallic oxidation. Good Luck.
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]
     
     
     
______________________________ Reply Separator _________________________________
Subject: PCB board age
Author:  [log in to unmask] at ccmgw1
Date:    9/16/96 4:43 PM
     
     
We stuff and solder (both wave and hand) small runs of PCBs (primarily PTH 
components. Our boare board requirements include individual packaging and 
boards no older than 6 months. A supplier recently shipped us boards that 
were re-reflowed 9 months after their original fabrication. Is this 
acceptable within A-610 for hi-rel commercial applications?  Thanks.
     
Tom Moore
Electro Plasma 
Tom Moore
     
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