My loss is your gain: had to patch another Fomu. For multiple reasons USB D- wasn't connected (D- pogo pin in wrong location / D- solderball not connected) and so I made another sample to help locate the test jig issue. This time I bypassed an eyepiece to film it - enjoy!
pic.twitter.com/YODk2qtJQx
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Replying to @bunniestudios
Wow. That's amazing. I haven't had the need to rework a BGA, but now I'm inspired to find my own balls to play with (couldn't resist it). Nice vid!
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Replying to @freaklabs @bunniestudios
I should probably clarify. I've never needed to rework a BGA because my lazy butt would just wait the two weeks and respin the board. Never knew there was a technique to soldering jumper wires underneath a CSP.
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Replying to @freaklabs
It's amazing what you can learn on the streets of Shenzhen
Sometimes I peek into the SMD repair shops and glean a technique or two. Some might even say I stole/copied their trade secrets.
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Replying to @bunniestudios @freaklabs
I didn’t know you could get UV soldermask. Off to look for some now! This is also why I miss going to Shenzhen.
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Replying to @N1FIY @freaklabs
This is the tube I'm using in case it helps.
#todayilearned it also partially cures with heat.pic.twitter.com/DAOaEULHhw
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Temp definitely impacts UV cure speed too. I’ve noticed much much longer times when in a cold (40-50F) garage. Nice rework! What’s the reason for wire next to & not under? I think there may be some tweaks to simplify the positioning part of this.
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Wire under leaves no space for the solder, so you either get the ball pushing up the CSP causing disconnects, or excess solder shorting to neighboring balls. Putting it next to the ball causes the molten solder to wick onto the wire, away from neighbors & preserving planarity...
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Ah interesting. What ball size and pitch? What’s the wire gauge? I want to test a few things like hammering the end of the wire flat.
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0.4mm pitch, 0.27mm diameter balls. The wire is 0.1mm diameter, so I guess 38 AWG? Hmm, hammering the end of the wire flat is a clever idea, I hadn't considered that...
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