My circuit board contains 11 x 11 matrix 1mm pitch BGA, The device was tested in socket on evaluation Board. We handed over the actual PCB & devices for re-flow. The assembly house first re-flowed all the SMT components other than BGA. BGA was placed after first re-flow, Micro stencil was used for dispensing solder paste. It was reflowed using a BGA rework station,After attaching the device , the Board was not functioning and the problem is traced to BGA. when inspected, we found the outer rows of the BGA balls are melted excessively. Edges of the BGA is warped to the board side. But X-Ray shows no solder bridging. But smallar sized BGA pad is seen on 2 nd column & 3rd row from bottom. Is there any other problems ?. What could be the root cause ? Pictures attached.
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