Underfill chips

[Adenitz]

Hello,
Today I saw a video from PLD in which he replaced two chips CD3215 that had underfill. It was pretty complicated procedure of removing the chips and cleaning the board. What exactly is the purpose of underfill? Is it to protect chip‘s pins from liquid damage, to improve resistance to stress or shocks or something completely different?

Thanks.

[mon2]

Re: Underfill chips

https://www.henkel-adhesives.com/ca/...hermal%20shock.

[reformatt]

Re: Underfill chips

Mainly to prevent movement of the chip and cracking the balls. But board flexion/shock on a MAC is very minimal (compared to something like a phone). Phones maybe, but MAC's? CD3215's are on the edge of the board, so board flexion is going to be almost non existant.

It's there to hinder repairs, pure and simple. Liquid resistance could be accomplished in many other ways, but I wouldn't say MAC's give any consideration to that in their designs.

[piernov]

Re: Underfill chips

Several MacBooks have been subject to physical stress on the board causing problems. Somewhat common RAM slot issue on 820-3115, common GPU VCore controller issue on 820-3332, less common GMUX problems on the older A1286, possibly also the cause of the common CPU-related failure on A1534…
They did fix the 820-3332 problem on the following A1398 machines at least.

Not sure it was really necessary to underfill the USB-C controllers though. At least it's a very good protection against liquid damage but I doubt it was the intended purpose.
Sadly it indeed it makes the work harder when the failure is caused by something else.

[ugamazing]

Re: Underfill chips

Thankfully, Apple removed the underfill (on USB-C controllers, anyway) on boards after 2017. They probably realized how commonly those chips need replacing, and their own repair facilities likely had to deal with the underfill as well. But the 2016/2017 boards...ugh. The underfill still exists around nands/WiFi ICs and things, but not the CD321* controllers anymore.

I've read of some certain types of underfill-specific solvents (and acids I think) that can dissolve the underfill in certain cases. But, I've not any experience with them and don't know if any exist for the specific underfill used by Apple.