|Ask the Experts|
August 4, 2008
Reflow PCB with BGA's and CSP's
We are trying to reflow a PCB that contains both BGA and CSP's. During reflow we are seeing solder being sucked into vias, rather than being consumed by the BGA balls. Is there a way to keep this from occurring?
|Expert Panel Responses|
Unused vias should be protected from pulling the solder off BGA pads and any other pads for that matter and this is usually accomplished by using solder mask or solder resist to tent the unused vias. Check IPC-A-600 REV G, page 40, 41, and 42 for information on how this should be requested from your board suppliers.
Vice President, Technical Director
Couple of ways to approach this problem.
Vice President Technology
There are two common solutions; one would be to apply solder mask over the open vias, and the other is to redesign the board with dog bone shapes so that there is a small trace between the pad and the via. This will prevent the solder from migrating across the pad and down the via. Can you turn down the temperature of the subzone of your oven? This might be the easiest solution, as solder flows to areas of highest temperature. This might just work.
Regional Sales Manager
OK International Inc.
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