Hi Jan-
     
     I would suggest taking a look at how/where the shield plated thru 
     holes are connected to the internal board planes. If those plated thru 
     holes are connected to several of the internal planes then you have a 
     heat thieving condition impacting your ability to solder. Check with 
     your design folks and see if there is any possibility of getting some 
     relief or minimization the internal plane connections. You can also 
     look at adding a small amount of solder paste at the shield base to 
     help promote solder filleting - the solder paste will reflow during 
     wave soldering due to the temperatures involved. Good Luck.
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]


______________________________ Reply Separator _________________________________
Subject: SMD remelt
Author:  [log in to unmask] at ccmgw1
Date:    4/9/97 3:15 AM


Hi all,
     
We have a minor problem at wave soldering shields on 8-layer FR-4.
The problem is that we need a very long dwell time (6-8secs) to get the 
solder to wet all around the shield, it's very critical because it has 
to be a tight joint. This leads to a high temperature at topside of the 
board at soldering, and inside the shields we have SMD-ICs which joints 
reach an temperature to about 209 degC. 
But then if i raise the preheating temperature and lower the dwell time, 
the shields won't get this tight joint and misses corners and some 
long-sides, this cost some to rework.
Some additional info: Seho wave solderer, NO-CLEAN flux, We put some 
extra flux around the shield, we use a chip-wave to get better wetting. 
Anyone have more ideas?
     
/Jan Merstrand
Wave Soldering Technician 
     
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