Hello,
I have been having some troubling issues when it has come to BGA Placement and I was hoping if there have been others who have been able to resolve similar issues.
We are curently doing reworks on a variety of BGA, but seem to be having issues with only one particular PCB. The issue I am currently having is that we seem to be having intermittent failures when it comes to placing our 38mm x 38mm BGA onto the large PCB (nearly 40cm X 25cm). Our success rate seems to be rather low (around 60% to 70%).
Naturally the first thing I went after was my profile on the APRXL5000 OKI Device, but after numerous and expensive X-Ray and Barascopic analysis, we could not tell that there were any issues with the placement itself. Furthermore, the amount of warping that is occuring seems to be controlled to a minimum, which was extremly difficult to get to considering the size of the PCB and component.
We are currently baking the BGA on a weekly basis, and depending on the moisture level on the BGA, we bake them every 72 hours. We are also buying the components directly from prominent sellers. Also the fact that we are able to get a success rate higher than 50% shows to me that the components themselevs seem to be reliable.
The issues we are seeing after the placement itself is that the component exhibits symptoms as if it were shorted internally. As we do X-Ray analysis, we found to be no bridges or any other such issues with warping, open or voids. We were even concerned with the Head-in-Pillow effect that are discussed in other discussion forums. This was ruled out upon when we removed some of these faulty components. We found that the pads were sufficently connected by examining the remaining solder residue on them. We are currently at a loss on explaining what the possible causes of our issue is.
We are using a Dual Heater which has 5 zones to rework the component. A scrap board was used to develop the profile, where holes were drilled at different points in the area. I made the profile to ensure that the Temperature Differential does not exceed 15 Degrees C. The profile along with the support bars ensure that the PCB does not overly warp.
We finally ensured that the issue was related to the component itself by lifting the BGA and testing the board for shorts and other issues. These tests showed no issues with the PCB once the BGA was lifted. We can tell that the BGA is the root cause of the problem, but not why.
I am not sure at which temperature the wire bonding in a BGA geos critical and breaks. Would anyone know if that is a possibility, because the Broadcom BGA which we are working on currently has a built in thermal conduit from the top of the BGA where an external heatsink can be attached.
Have others come across similar issues? If so, have there been resolutions to such issues?
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