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Comment by dishsoap | Hacker News Reader

I wonder what the reasoning is for grinding off the old chip instead of desoldering properly? Maybe the heat would damage something?

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It's hard to see but the original NAND is epoxied to the motherboard, which wouldn't come away easily with heat. I'm not sure what the purpose of the epoxy is but he goes to the trouble of replacing the epoxy later in the video so there must be a good reason for it.

The epoxy protects from physical shocks and also helps manage the effects of thermal expansion, either of which could crack solder joints over time.

Ah, not taking any chances after bumpgate.

Apple has been epoxying BGAs at least as far back as the iPod nano 1st gen, released in 2005

I’ve seen some fascinating slo mo videos of devices bouncing from a decent fall in an X-ray machine. The battery in particular squishes way more than you think should be possible or right. Epoxy makes a ton of sense when you consider the shock that it takes.

It's called "underfill" and it's common for BGAs since the chip doesn't have the same thermal expansion as the PCB

The chip has an epoxy underfill. It softens slightly in the heat and desoldering is probably possible, but the amount of force required means you're likely to damage something in the process.

From the creator, in a reply:

"CNC is the safest and most efficient way. Using a hot air gun to remove it normally will cause irreversible damage to other components on the motherboard."

Yet, he uses hot air gun to solder the new chip. There are ways to safely remove that old nand chip, but why would they show the state of the art methods?

The epoxy below the original chip would require a lot more heating to remove than soldering in a plain chip.

CNC drill removal is safe and can be done consistently by a machine with consistent predictable results.

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