If I understand this question right, then the undesirable reflow condition 
 on the topside could be caused by the extra thickness of copper acting as an 
 additional heat sink.  The board would therefore need extra heat in order to 
 solder.
 
 A way to design around this could be the use of thermal reliefs on holes 
 that connect to the planes.  This would limit the heatsinking properties of 
 the internal power and ground planes.
 
 Another thing to look at would be the copper weight on the internal planes.  
 Could these be reduced and still meet your design criteria?
 
 Finally, how much plane area is on the outer layers?  These also tend to be 
 heat sinks during soldering.
 
 


______________________________ Reply Separator _________________________________
Subject: ASSY: Topside Reflow on .062 boards
Author:  [log in to unmask] at SMTPLINK-HADCO
Date:    5/6/96 10:43 PM


 
Text item: 
 
Does anyone have any data on topside reflow on 4L boards? 
We are seeing reflow on .062 4L boards and the thought is that the I/L copper 
thickness is different for reflowed vs non reflowed boards. The boards that 
reflowed showed ~.002" copper while the non reflowed boards showed ~.0012" 
copper. The data is not statistically valid--too few samples.
The construction is single ply 7628 for L1/L2 and L3/L4. Inner layers are 
planes.
 
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