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BGA REWORK ISSUE

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#69692

BGA REWORK ISSUE | 3 July, 2013

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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#69694

BGA REWORK ISSUE | 3 July, 2013

Hi, I had seen your post earlier but had lost my very old log on information. First I will say that BGAs should never be placed and re-flowed with a rework station unless there is absolutely no other option, so I don't understand why your assembly house did what they did. There are 2 things that could have happened to the smaller pad in the lower left. 1. The ball was missing. 2. There was a break down in the solder mask between the pad and via and the ball wicked into the via. However the x-ray doesn't indicate that. I also noticed that the pads in the upper right quadrant appear to be larger. Possibly the PCB pad geometry was not consistent with the others, or the rework station nozzle was making contact with the part which would explain the warping toward the board you mentioned. Unfortunately to me it looks like this BGA needs to be removed, re-balled and re-attached. These are just some thoughts in general. It is not possible to determine root cause without knowing many other things in the design and process. Good Luck

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#69721

BGA REWORK ISSUE | 8 July, 2013

The smaller ball "missing" from the lower left is from solder migrating down into the adjacent via. The solder mask may have been damaged or missing prior to mounting the BGA device. The larger balls at the top right are due to uneven heating during the mounting. That your assembly house did the SMT parts separate from the BGA device is a red flag for me.... Just my $.02 'hege

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