|Ask the Experts|
September 2, 2009
Mysterious Solder Balls
We are facing issues with a double sided board assembly, after bottom side reflow. In some of the fine pitch component locations, solder balls are popping up from via holes causing bridging. What might be causing the solder ball problem and how can we prevent it?
|Expert Panel Responses|
This could be attributed to couple things: Is the solder finish HASL? As solder finish may not be applied to clean copper and the HASL thickness could be plugging the via holes. Other options which could affect solder via hole intrusion. Solder aperatures in the stencil are allowing solder to enter the hole. Solder is wicking from pad of logic device, into via hole. You might allow your assembler or PCB fabricator to solder mask the holes. Tenting the vias on the topside will prevent solder paste intrusion in to the pads.
Capital Equipment Operations Manager
Specialty Coating Systems
It sounds like you are overheating the previously reflowed side of the board, during the second reflow operation. This is causing the solder to flow out of the vias onto the PCB. Try turning the temperature down on the subzone of the reflow oven.
Regional Sales Manager
OK International Inc.
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