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To my understanding BGA reflowing is a technique which aims to reconnect bad solder joints on a BGA chip, BGA reballing is a technique to desolder and then resolder a BGA chip both aim to do the same thing although the latter seems like a more "clean" way to do it.

However I've read multiple times online that these techniques are often used during GPU "repair", sometimes with dead GPU chips which will give the illusion that the resoldering of the BGA joints underneath the chip are what repaired it, whilst actually it's solder joints inside the chip which melted and reconnected to the die that repaired it.

This prompted me with a couple of questions, Is this true? If we had a GPU with bad BGA solder joints and we wanted to reball it how would we do that without damaging the insides of the chip, could we possibly use heat resistant tape or something similar? How would you actually repair a dead GPU chip?

Edit: https://www.ifixit.com/Answers/View/440780/reballing+a+PS3+actually+works+or+not+,+and+how+long+it+lasts.

See the second comment in the thread, there's a person who explains it in more detail.

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  • \$\begingroup\$ about 12-13 years ago I had a IBM Thinkpad with a BGA GPU. It was known to fail sometimes due bad soldering (the process was new for so large chips it was said). It was "repaired" with just put it back to the reflow oven without desoldering/reballing. In fact we use reballing in development when a BGA Chip needs to be tested outside of the board or when you have a low number of prototype chips and soldered one to a bad board. So putting it on a working board sometimes is a high value. \$\endgroup\$
    – schnedan
    Commented Feb 12, 2022 at 8:16

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The melting point of the internal (flip-chip) package to die solder is a higher melting point than the external balls. This allows the BGA to be soldered in the first place.

So it can be re-balled and used again, once it’s been tested, without disturbing the die attach.

Which brings me to the most common use of reballing: failure analysis. The ‘failed’ chip removed from the board, is RMA’d, then reballed and retested using the ATE fixture.

This is valuable to the manufacturer as feedback on their test coverage, but it also ensures that you don’t mount a dead chip onto your board (boards can only survive a couple of removal/replace cycles before issues like pad lift begin to happen.)

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  • \$\begingroup\$ Thank you for your answer, could you read the edit? Is it just bogus or is there something which leads him to think this is the case? It makes sense that the the internal solder joints have a higher melting points, like you said otherwise the whole concept of reballing wouldn't make very much sense. So I assume as long as we stay below that melting point we'll be fine, now if one of those internal solder joints would be bad how would we go about fixing that? \$\endgroup\$
    – icyli2
    Commented Feb 12, 2022 at 3:35
  • \$\begingroup\$ You wouldn’t in most cases. While it’s possible to detach and reball a die, then remount it on a substrate, the whole process is too expensive except for the very most expensive ICs like big FPGAs, and then only if FA is to be done. It’s not worth it for a GPU. Also, the vendor can use x-ray to inspect for bad flip-chip joints and thus identify that as the failure point. \$\endgroup\$ Commented Feb 12, 2022 at 7:10
  • \$\begingroup\$ Very insightful, makes more sense now especially when you mention x-ray to inspect the flip-chip joints. I assume GPU manufactures such as Sapphire for example would also get details of the melting point of the internal solder in the flip chip and develop a special heating curve? And pair that with x-ray and other checks to ensure the internal solder joints aren't damaged when soldering on the chip to the PCB for the first time? How would a tech repair shop ensure that the issue is a bad solder joint inside the flip chip given they don't have access to an x-ray machine? \$\endgroup\$
    – icyli2
    Commented Feb 12, 2022 at 22:26
  • \$\begingroup\$ And in factories, when a BGA chip is soldered on for the first time, would they typically heat it from the top (which would heat the flip chip as well) or heat the solder joints from the bottom, then go about placing it on the PCB? \$\endgroup\$
    – icyli2
    Commented Feb 13, 2022 at 0:02
  • \$\begingroup\$ BGAs are mounted in an IR reflow oven, using a specific pre-heat then peak-heat cycle. Heat is applied to both sides of the board. Also, the board has solder paste applied prior to placing the components. \$\endgroup\$ Commented Feb 13, 2022 at 0:13

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