If you are making product to an IPC class 2 requirement then you only 
     need 50% fill (see page 52 in the IPC-610 book figure 4-2).  Also in a 
     previous life we had a 15 layer board that had  the same problem and 
     the way we were able to cure this was at the end of the wave solder 
     process we would bring the board around before it had a chance to cool 
     to much and run it right through the wave solder machine again.  By 
     doing this we were able to keep the board hot enough that as it went 
     through the wave solder machine again we would get good flow to the 
     top side .  
     
     Good luck.


______________________________ Reply Separator _________________________________
Subject: ASSM:  Top fillet formation
Author:  [log in to unmask] at _internetcc
Date:    12/20/96 3:49 AM


Hello Technetters,
     
I need some advises. I have a  6- layers board. I try to wave solder it, 
the solder 
at the ground point is not able to flow up to the top side of the board, in 
fact, it
doesn't flow above 75%.
     
We have tried using a solder-iron and set to temperature to 450 deg. cel. and 
hopefully able to force the solder through the PTH. Too bad, it didn't work 
anyway
and it in fact has caused some lifted pads.
     
We use full blow Nitrogeneous wave-solder machine, and the flux we use is 
only 1.2% solid content. And if the preheat temperature set to high, the flux 
gets degraded before it even reaches the wave..
     
I would like to know if anyone could advise me how wave-solder such a board 
with a great heavy thermal mass.
     
Thanks in Advance..
     
     
     
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