BGA reballing techniques and equipment

[Joe24]

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.

[diif]

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.

[Joe24]

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.

[diif]

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.

[Joe24]

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.

[diif]

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.

[Joe24]

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.

[diif]

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.

[Joe24]

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....

[diif]

Re: BGA reballing techniques and equipment

Its says Amtech and it is genuine Amtech.

[Joe24]

Re: BGA reballing techniques and equipment

Well I'm trying the exact method as you've outlined, and I have yet to successfully reball a chip using the stencil holder and Amtech 559 flux (there are 2 different variants of 559, I'm using NC-559-V2-TF). Made 5 different attempts this afternoon, varying the process a bit each time. So I'm calling BS here. You must be working with larger pitch chips or something. Or are drastically misrepresenting your success rate with this method. Invariably, a bunch of solder balls run together, and I spend the next couple hours removing bridges and manually replacing solder balls in the damaged areas. Or just starting over. Tedious and frustrating, to say the least. Have tried various amounts of genuine Amtech 559 flux, down to a layer so thin that it won't even hold the solder balls in place. No joy. What are you doing different?

[Joe24]

Re: BGA reballing techniques and equipment

This is 0.45mm solder balls on 0.7mm or so pitch. Specifically, an Nvidia GP106 GPU.

[diif]

Re: BGA reballing techniques and equipment

Well I'm trying the exact method as you've outlined, and I have yet to successfully reball a chip using the stencil holder and Amtech 559 flux (there are 2 different variants of 559, I'm using NC-559-V2-TF). Made 5 different attempts this afternoon, varying the process a bit each time. So I'm calling BS here. You must be working with larger pitch chips or something. Or are drastically misrepresenting your success rate with this method. Invariably, a bunch of solder balls run together, and I spend the next couple hours removing bridges and manually replacing solder balls in the damaged areas. Tedious and frustrating, to say the least. Have tried various amounts of genuine Amtech 559 flux, down to a layer so thin that it won't even hold the solder balls in place. No joy. What are you doing different?

What equipment and technique are you now using that is different from your first post ?

[Joe24]

Re: BGA reballing techniques and equipment

Was using direct heating stencils. Now trying a reballing jig that takes 90mm stencils. The kind you mentioned, with the removable top and a slide vise that holds the chip. Direct heating stencils are okay for small stuff, but once you get up to the bigger GPUs, stencil warping becomes a huge issue. Also changed to Amtech flux, which is what the internet says I should do.

[Joe24]

Re: BGA reballing techniques and equipment

The problem is that the solder balls run together after I remove the stencil, and even more so when I begin applying heat and the flux warms up and gets thinner. Probably 100-200 solder balls to replace manually every time, which is getting close to 10%.

[diif]

Re: BGA reballing techniques and equipment

How are you applying heat ?

[Joe24]

Re: BGA reballing techniques and equipment

Hot air soldering gun at minimum fan, with the snout removed for minimum air velocity, and a decent distance away (4"). Some balls are running together before I even start heating, so that's at best only part of the problem.

[diif]

Re: BGA reballing techniques and equipment

You need to use indirect heat if you're not using direct heat stencils. I place the chip on my hotplate after the balls have been placed.
Balls shouldn't be running together before you've added heat.

[Joe24]

Re: BGA reballing techniques and equipment

Oh I agree with you there, they really shouldn't move. Anyhoo, what type of hotplate do you mean? One of those smooth-top ones they use for removing phone screens, or the ceramic circuit board preheater style? I might give it a go in my bench oven (former toaster oven). If you're talking about the smooth-top heaters, I don't see that working on a GPU, because the die is considerably smaller than the BGA base. Especially a GP106.

[diif]

Re: BGA reballing techniques and equipment

A Honton HT-2020.