Solder preferentially wicking up the leads rather than uniformly over 
     the lead foot and pad sometimes is an indication that the component is 
     reaching reflow temperature much earlier than the printed wiring 
     board. Try hooking up some small thermocouples on both the lead and 
     board pad to see if a change in the heating profile will remedy the 
     problem. A second possibility is that your baking operation is 
     oxidizing the board pads to the point the component lead is more 
     wettable than the board pad. Good Luck.
     
     
     Dave Hillman
     Rockwell Collins
     [log in to unmask]
     


______________________________ Reply Separator _________________________________
Subject: ASSY:Solder Wicking,Fine Pitch Leads
Author:  [log in to unmask] at ccmgw1
Date:    9/19/96 7:37 AM


We are seeing instances of solder wicking up our fine pitch leads and 
causing minimal solder left in the joint to wet the board. What do most 
companies do about solder wicking up fine pitch leads? What can be done to 
minimize this phenomenon?  Does anyone have suggestions that have been 
successful for you? 
Some background process info:
We profile at approximately 215-220 degrees c. 
We are using RMA solder paste.
We are baking our boards (multilayer) prior to reflow soldering. They are 
cool for the print cycle.
We are over 183 degrees c for approximately 70-80 seconds. 
We are using a Vitronics 722 IR oven.
     
Any comments would be appreciated!!! Thanx! 
----------------------------------
Jeffery L. Hempton              Phone: (219) 429-7335   Fax: (219) 429-4688 
Hughes Defense Communications                           Mail Stop: 25-31 
1010 Production Road, Fort Wayne, IN 46808-4106
Email: [log in to unmask]
     
"The reason most people do not recognize opportunity is because it is 
usually wearing a pair of bib overalls and disquised as hard work."    - 
-Thomas Edison
     
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