Dear Guenter
     
     Thank you for your advise and I would like to have the 3-
     D graph for reference.
     
     My fax number is (852)27992398.
     
     Best Regards,
     
     KP Chan

    
______________________________ Reply Separator _________________________________
Subject: Re:Solder blow-out in soldered PTH assemblies
Author:  [log in to unmask] at Inter-net-Linkage
Date:    12/31/96 8:29 PM


Dear KP Chan
     
Blow out of PHT solder joints is not only a question of the copper 
thickness but also of the moisture contents of the board and, very 
important, of the quality of the drilled hole. If the PCB manufacturer is 
using the drills too long or if he's feeding too much while drilling ( 
price pressure ) you will find ripped out glass fibres causing hollow 
sections as well as glass fibres reaching out of the drilled walls. Both 
cause a porous copper plating of the holes no matter how thick the final 
plating is especially because the first process step of plating, where the 
walls of the holes are covered electroless with a layer of copper in order 
to make galvanic plating possible, will not cover all these irregularities. 
Give me your Fax number. I can send you a 3-D graph where the average 
amount of voids in a solder joint vs. the average copper thickness and the 
number of not metallized glass fibres after the electroless copper plating 
is shown.
     
Best regards
     
Guenter Grossmann
Federal Institute of Technology
Reliability Laboratory
Zurich
     
     
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