Well, as someone who has reworked a few BGAs in his time... I figure I can pop in here and show you guys a link to my other post here: http://www.gp32x.de/board/index.php?/topic/52920-some-questions-about-the-hardware/page__view__findpost__p__838902
No sense in typing that out again since it's all still there... so yeah, it's doable if you're REEAAALLY good at soldering, have the right equipment, and are willing to take the risk.
I wouldn't do it, and I'm the only person I know (in person, duh) who's ever actually been successful in replacing a BGA... just the normal kind of BGA too, not one of these package-on-package ones.
I can comfortably claim that I may be the most skilled solderer on these boards and not be excessively "puffing my chest" so to speak. I know I'm the most skilled at my workplace so this claim isn't too far out there. Notice I say that I MAY be the best... because I really don't know who else is out there or what their skill with liquid tin and lead is and the last thing I'm trying to do is offend, challenge, or make light of anyone else's talents.
Hopefully you get my point as I intended it: if a guy who's good enough to make a claim of possibly being the best soldering hand on the boards AND gets paid good money to be that good at soldering wouldn't try replacing the CPU/RAM BGA package-on-package assembly on his Pandora, then neither should you unless YOU'RE good enough at soldering to make similar claims.
QBJECT said:
Isn't the Package-on-Package connection the sort of thing that would have to be wave-soldered? I can't imagine there'd be any way to redo that with the OMAP attached to a populated board, what with the, y'know, immersion in hot solder that the wave process requires.
Actually, wave soldering is used for through-hole only... these parts are surface-mount. Additionally, during the wave solder process, printed circuit boards do NOT actually get submersed. Instead, a conveyor that only holds the board by the edges brings the boards down to the surface level of the molten pool of solder and glides it across the surface with the bottom of the circuit board just barely touching the solder. Surface tension then soaks the liquid solder up into the holes and accomplishes all that soldering for you. If the circuit board were to actually be submersed in the liquid solder, all the components on it would burn up.
All the parts for our Pandora motherboards are surface-mount and likely assembled by pick-and-place machines. Which means they "silkscreen" a sticky solder paste onto the surface of the circuit board and then run it through a pick-and-place machine which uses air suction to pick up each component from a tape-and-reel and then place it onto the appropriate place on the motherboard. Then after the machine places all the components onto the board it will send the board on to an oven which will bake the entire board slowly and evenly (to avoid warping of the board from the heat) up to just hot enough to melt the solder paste. The paste is sticky enough to hold the components in place until the boards go though the oven.
BGAs usually come "pre-balled" meaning the balls of solder that act as pins are already attached to the bottom of the chip. A pick-and-place machine still places them onto the circuit board but you don't silkscreen solder paste onto the pads first. Instead it would just be some tacky flux to hold the BGA in place until it gets to the oven.
At my company, we have our blank circuit boards go thru the pick-and-pull machines first to get only the BGAs attached. After the BGAs are done baking onto the board, the board is cleaned before being sent through the pick-and-place machine again for all the rest of the parts to be attached with the solder paste. Then after baking and cleaning one more time any through-hole parts are attached by hand. This is industry standard manufacturing techniques so I don't see why the Texas factory would be doing it any different.
Sorry to be so wordy... hopefully now you know a little more about how our Pandoras (and other electronic gadgets) are made and found what I had to say interesting... my apologies if it is not so.
darkblu said:
as a curiosity, i've heard of some ungodly machines used by silicon vendors (particularly AMD, but i'm sure all big fish have such) to literally patch a die post-production. to save time from re-spins of pre-production silicon, etc. think electronic microscope^2 -level of complexity & cost. also, i'm not sure if those would be still viable today as that was circa 130-90nm times.
I have a friend who works at Intel... he gets to play with one of those on a regular basis and oh yeah they still use them for the latest and greatest cutting edge stuff. I forget what they're called exactly, but these machines are used during the prototyping stage more than the actual chip manufacturing process. The chip developers leave extra silicon in there and the machine can focus a laser into the right spot to turn non-conductive paths into conductive ones in the silicon... my friend told me that during prototyping sometimes half of what's in the chip is dead silicon so they have the flexibility to make modifications with these machines. It's a lot cheaper to do a little laser surgery than it is to have a whole new prototype silicon die made.
