edwin_on_reddit

Are there any new breakthroughs in developing more reliable lead free solders? Thanks a lot for doing this. I understand if my question isn't in your domain.

For a class project we dissected the PCB of a 2010 model phone (HTC Incredible). To do that we cross sectioned and x-rayed many of the chips to inspect them. One of the mysteries we encountered was explaining the layout of the BGA of this chip. The footprint of the package takes up roughly the size of the frame of that picture. The BGA's partially populated square center pattern was typical of many other chips this size. However the parenthesis-shaped "arms" were a very strange shape, but we had no idea why. Would you care to hazard a guess? This is a Hynix 8 Gb memory chip. I will edit this comment to include a spec sheet shortly.

I can't pull up the datasheet, but the part number is h26m44001car. There were no TSVs in this chip (that we knew of). 1st level interconnects were Au wirebonds that went from the stacked silicon to the chip carrier. We also thought that they might be to anchor the chip down, but then again, why would you want to do that? Putting BGA balls farther away from the neutral axis will increase thermal stress on them. Wouldn't the underfill alone suffice to anchor the chip at the edges?