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Old 10-14-2021, 03:59 AM   #1
Joe24
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Post BGA reballing techniques and equipment

I work mainly with larger (2000-3000 ball) BGA chips, typically 0.4-0.55mm solder balls. I've reballed many of these, and it's always a royal PITA. My current system is direct heat stencils and hot air, which works but is very tedious. Typically takes me 3 hours, which is about 2 hours too many. And to make matters worse, today i discovered that one stencil must be warped, because as soon as I apply heat, 1/3 of the stencil lifts away from the chip and all the solder balls run together. Unfortunately that's the only stencil I have in that size, atm. You know... we've all had weeks like that.

So, what materials, stencils, flux, techniques, tricks, etc. do you guys use? There's gotta be better ways to do things. Please don't just be all grandiose and vague ("Use better stencils!" without specifying exactly which stencils are 'better' in your opinion, etc.). If you have something that works, I'd like enough information so that I can go buy it myself.
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Old 10-14-2021, 04:09 AM   #2
diif
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Default Re: BGA reballing techniques and equipment

You need to identify where the time is going.
I use Amtech 559 flux and indirect heat stencils in a holder.
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Old 10-15-2021, 12:48 AM   #3
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Default Re: BGA reballing techniques and equipment

Time goes to initial cleanup, solder ball placement, inspection, and patching defects. 559 flux holds the balls in place? I've never used indirect stencils, don't know much about them.
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Old 10-15-2021, 01:38 AM   #4
diif
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Default Re: BGA reballing techniques and equipment

Clean up is quick, a large blob of leaded solder followed by some Chemtronics braid, done just after the chip has been removed whilst there is still some heat in the board.
Placing the balls and ensuring only one is in each hole is the most time consuming part. I tip some balls into the stencil holder and tilt it so they fill all the holes, then tip out the excess.
Yes, 559 holds the balls in place, the lightest of smears is required.
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Old 10-15-2021, 09:26 AM   #5
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Default Re: BGA reballing techniques and equipment

Sounds faster than what I'm doing. I dump a bunch of solder balls on top and chase them around with a Q-tip. Direct heat stencils don't have a stencil holder around them to stop the loose balls from leaving town. 559 must be better at keeping stuff in place than what I'm using. Flux I'm currently using is some ChipQuick water-wash stuff, which is okay for some things, but yeah the balls would run all over the place if I removed the stencil like your method.
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Old 10-15-2021, 09:53 AM   #6
diif
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Default Re: BGA reballing techniques and equipment

You could make a little wall around the stencil with some plasticine/modelling clay/blu tac to stop them rolling away.
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Old 11-01-2021, 03:18 PM   #7
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Default Re: BGA reballing techniques and equipment

Can't buy Amtech flux in my country. Seems to be a US-only thing. There are all kinds of Chinese fakes available, but the real thing doesn't seem to be available.
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Old 11-01-2021, 05:19 PM   #8
diif
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Default Re: BGA reballing techniques and equipment

Yes, there are plenty of fakes but it's not just a US thing. I bought mine in the UK off Ebay.
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Old 11-02-2021, 12:15 AM   #9
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Default Re: BGA reballing techniques and equipment

Just because it says Amtech... if you got yours from eBay, I'm almost certain that you're not using genuine Amtech.

Anyhoo, Amtech themselves will sell to my country from their website amtechdirect.com, so we'll give 559-ASM and 213 fluxes a go.

I've since been reamed out by multiple people for using water-wash flux for reballing. I didn't find it very good anyway, turns real watery and runny when it gets hot, beads up like water does, which is why the stencil needs to stay in place until the balls are fused. But they also say the residue from water-wash flux is a problem. Even though the stuff I'm using (ChipQuik SMD4300TF30) says no-clean and I don't use more than a thin smear, the fact that it's water wash apparently means there are some nasty corrosive detergents left under the chips. And it's also hygroscopic as hell, which doesn't help the corrosion issue. I know from experience that it's a pain to clean up with Q-tips/IPA99, seems like you can never get it all. And after a couple heat cycles, more residue spreads out from under the chips....

Last edited by Joe24; 11-02-2021 at 12:20 AM..
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Old 11-02-2021, 01:44 AM   #10
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Default Re: BGA reballing techniques and equipment

Its says Amtech and it is genuine Amtech.
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