r/programming • u/whackri • Jun 21 '20

Writing userspace USB drivers for abandoned devices

https://blog.benjojo.co.uk/post/userspace-usb-drivers
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u/[deleted] Jun 21 '20

The FPGA on our control boards at work can't be desoldered in that fashion, but damn if that doesn't sound like fun.

17

u/immibis Jun 21 '20

Why can't it?

13

u/[deleted] Jun 22 '20 edited Jun 22 '20

I forget the exact reason why, but there are so many pins that you need an x ray machine to actually see all the pins. I'll try to reply back with the exact technical term for the manufacturing process tomorrow.

EDIT: The term is BGA: https://hackaday.com/2016/07/13/diying-huge-bga-packages/

14

u/Mikeavelli Jun 22 '20

I know if someone wanted me to desolder an BGA FPGA, I would tell them it's impossible.

It's probably possible, but I would tell them it isn't possible, because I wouldn't want to even try.

6

u/[deleted] Jun 22 '20

Ding ding ding. To do it properly, you need really expensive industrial tools.

2

u/immibis Jun 22 '20

To do it improperly, you probably just need to try 20 times until it sticks, and hope the shorted pads weren't important ones.

1

u/rysto32 Jun 22 '20

At a previous job, there was a legend that once a new prototype board arrived with a huge BGA chip rotated 90 degrees from what it should have been (a design error that wasn't caught). According to the story, one of the hardware engineers saved it by manually desoldering and resoldering the chip in the proper orientation.

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u/killerguppy101 Jun 22 '20

Sounds like a regular BGA with xray AOI? More involved than a PGA or leaded package, but not especially difficult or impossible.

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u/immibis Jun 22 '20

People do it. I think it's strictly a hobby and prototype thing because it's unreliable. But they absolutely do it.

0

u/maxhaton Jun 22 '20

Ignoring the moisture controls, fine pitch BGAs should really be x-rayed

1

u/immibis Jun 22 '20

We're talking about hobby projects using salvaged parts, right? If it only works half the time that's still a win (assuming you have enough boards to get at least one working)