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Old 03-14-2022, 08:25 AM   #21
myth77
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Default Re: BGA reballing techniques and equipment

My suggestion is to use direct heat stencils. In my expirience the indirect method will work only with bigger bga lik gtx 1070 or so...but with pch you need to be very carefull to work with indirect method.
I also started with indirect method..for me it made much more sense to use indirect heat stencils..and seems to be clearer method...But i didnt get good results and keep reballing same chip several times.... Maybe i am clumsy but i am just writing what i feel and have expirienced.

But when/if you use direct heat reballing it is very important to:

1. use a good quality stencil (one that will not warp easy) from trusted seller,
2. use a good flux,
3. before applying solder balls allways check with microscope assemblies for misaligned holes because it will not be easy to remove stencil from bga if holes were not aligned,
4. apply solder balls,
5. start with heatgun with low air flow...until stencil, solder balls and bga is slowly heating,
6. when you see that solder balls are melted remove heatgun and aplly flux direct on stencil...and again heat it with heatgun,
7. after that waith till everything cools,
8. try to remove stencil from chip but do not make to much preasure,
9. if its not coming off try using a heatgun again but just a little to melt the flux...and you should be able to remove stencil,
10. when stencil removed see if any solder ball is missing on the chip, if yes put it on directly on the chip and try to heat it again with heatgun,
11. clean it with isopropyl alcohol.

good luck!

Last edited by myth77; 03-14-2022 at 08:32 AM..
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Old 03-14-2022, 10:46 AM   #22
Joe24
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Default Re: BGA reballing techniques and equipment

GTX 1070 is the exact same BGA footprint as the one I'm currently working with. In my experience, this is pretty much the size limit of what direct heating stencils will do. Any direct heating stencils larger than this seem to warp no matter what you do or who you buy them from. Laws of physics at work: heating sheet metal causes it to warp. Ask anybody who welds. Which is why I'm trying to get indirect heating stencils to work instead, because I have a couple TU102 chips to transplant, and am not optimistic about direct heat stencils for the job.
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Old 03-14-2022, 11:13 AM   #23
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Default Re: BGA reballing techniques and equipment

Adding missing solder balls is easy. It's not so easy to clean up merged solder balls without nuking the rest.
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Old 03-14-2022, 11:41 AM   #24
mferna14
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Default Re: BGA reballing techniques and equipment

Everyone has different techniques. But I do it in a very differenct way, try it & one will never go wrong.

1) Remove all the old solder balls from the old chip with wick. Use solder Iron heat about 350. Once the chip gets hot you will notice how the wick makes its place & remove the solder balls & makes the chip smooth as ever.
2) Clean the chip with alcohol
3) choose the correct size balls
4) Now see the Chip's solder pad diagonally. You can choose any two point on the far end diagnoally. You have to solder JUST 2 BALLs (SAME SIZE) diagonally on either side so that the stencil sits in well & does not move. Again use less heat, around 300~350. The 2 balls on either side will melt on the solder pads of the chip.
5) Now add good BGA flux, spread with finger, you will get a smooth finish. DO NOT OVER FLUX, or the ball will bubble up from the stencil holes.
6) Align the Stencil, you will notice that with the 2 ball soldered diagonally hold the stencil in place & wioll not move.
7) Now put in the balls. I like to threw a few hundered of them & spread them out with a toothpick & the remaining I just add to the holes. Patience is virtue & surely will take some time but very enjoyable once done.
8) When all the balls are in place., see under MS. Time to use hot air. With low fan speed & heat 350, let all the flux melt & take in the solder balls & you see flux melting, DO NOT apply more heat & leave the chip to COOL DOWN for 2~ 4min. What happens is that the flux joins all the balls & the balls do not bubble up when applying heat next time.
9) Giving a finish. Now final stage, raise the air & heat a bit more. & you will notice that now after the chip cool down the ball do not bubble up & remain in place & start to melt on the chip's pads & once you see all are SHINNY, you are all set.
10) DO NOT CLEAN THE CHIP WITH ALCOHOL AGAIN AS PEOPLE DO as this flux will be helpful for soldering the chip again to the motherboard & later ULTRA SONIC cleaning with do the cleaning job. You can always use Hot air with low heat on the chip without the stencil to spread out the flux evenly.
GOOD LUCK & Hope you learnt something new. Thanks

Last edited by mferna14; 03-14-2022 at 11:54 AM..
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Old 03-15-2022, 02:26 AM   #25
myth77
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Default Re: BGA reballing techniques and equipment

Quote:
Originally Posted by Joe24 View Post
GTX 1070 is the exact same BGA footprint as the one I'm currently working with. In my experience, this is pretty much the size limit of what direct heating stencils will do. Any direct heating stencils larger than this seem to warp no matter what you do or who you buy them from. Laws of physics at work: heating sheet metal causes it to warp. Ask anybody who welds. Which is why I'm trying to get indirect heating stencils to work instead, because I have a couple TU102 chips to transplant, and am not optimistic about direct heat stencils for the job.
I have reballed several gtx 1070 and 1060 chips and didnt have any problem with warping...its just a quesiton of good stencil and patience with heating and airflow.

For chip that size i think you can go with indirect heat stencil and probably you will not have any problem with merged solder balls....
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Old 03-19-2022, 12:33 PM   #26
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Default Re: BGA reballing techniques and equipment

Tried using the indirect stencil on GP106 followed by heating in my bench oven. Still using Amtech 559. Better results than with hot air, but still needed to fix 30-50 balls (including the ones I had to remove and replace in order to clear the bridges; I take a needle nose tweezers and squeegee the bridge towards the nearest open area in the grid, which can nuke another half dozen balls if they're in the road).

You can see after stenciling where the solder balls are starting to wander around already. I baked the chip and jig all together, to minimize handling of the chip. Jig is all metal, not going to hurt it.
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Old 03-19-2022, 12:57 PM   #27
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Default Re: BGA reballing techniques and equipment

Quote:
Originally Posted by myth77 View Post
I have reballed several gtx 1070 and 1060 chips and didnt have any problem with warping...
Yes, but as I said, in my experience doing anything BIGGER than small GPUs like GP106/GP104 (37mm x 37mm) is an issue with direct heat stencils. I've done TU104 with direct heat stencils before, but it was dicey.

Nobody has trouble with warping when reballing a little GDDR6 etc. memory chip, because they're tiny. But the bigger the stencil, the more warpage you inevitably have. And I have some bigger TU102 GPUs to do (2080 Ti, which are 48mm x 48mm). Which is why I'm trying to get indirect stencils figured out, because direct won't work for something that big.

Last edited by Joe24; 03-19-2022 at 02:22 PM..
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Old 03-19-2022, 02:11 PM   #28
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Default Re: BGA reballing techniques and equipment

Quote:
Originally Posted by mferna14 View Post
2 ball soldered diagonally hold the stencil in place & will not move.
This is a really good tip for direct-heat stencils. I usually like to do about 5 balls on each opposite corner though. If there was only one ball on each corner, you're at high risk of ripping a pad off the chip if you bump the stencil.


Quote:
Originally Posted by mferna14 View Post
Spread them out with a toothpick.
Clean Q-tip works good too. If you get any flux on the fibers and solder balls start sticking to the Q-tip, chuck it and get a fresh one.

Last edited by Joe24; 03-19-2022 at 02:20 PM..
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Old 03-23-2022, 03:58 PM   #29
mferna14
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Default Re: BGA reballing techniques and equipment

Quote:
Originally Posted by Joe24 View Post
Tried using the indirect stencil on GP106 followed by heating in my bench oven. Still using Amtech 559. Better results than with hot air, but still needed to fix 30-50 balls (including the ones I had to remove and replace in order to clear the bridges; I take a needle nose tweezers and squeegee the bridge towards the nearest open area in the grid, which can nuke another half dozen balls if they're in the road).

You can see after stenciling where the solder balls are starting to wander around already. I baked the chip and jig all together, to minimize handling of the chip. Jig is all metal, not going to hurt it.
Just another Tip, the main idea of re-balling is NOT TO HEAT THE CHIP DIRECTLY, THE BALLs HAVE TO mellted on the pads. Try to heat the Balls directly with hot air when the stencil is on the chip. This does not get the chip very hot as the ball & the stencil both are acting as protective agents to the chip. AVIOD using the Toaster or what ever you are using, in this way you are applying heating the entire chip & it's core from TOP & BOTTOM.
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Old 03-23-2022, 05:26 PM   #30
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Default Re: BGA reballing techniques and equipment

Quote:
Originally Posted by mferna14 View Post
Try to heat the Balls directly with hot air when the stencil is on the chip.
That's the DIRECT-heating method, different stencils than what's shown in the pictures above. The stencils shown are the INDIRECT type, and are not designed to have heat applied to them at all.

Quote:
Originally Posted by mferna14 View Post
AVIOD using the Toaster or what ever you are using, in this way you are applying heating the entire chip & it's core from TOP & BOTTOM.
How do you think the chip gets installed on the board after reballing??? By "heating the entire chip & it's core from top & bottom," that's how. Don't worry yourself about heating the GPU when reballing, perfectly acceptable. Any BGA chip is tough enough to take normal soldering temperature for a certain length of time, usually 30 seconds or so at liquid-solder temperature, plus ramp-up and ramp-down time. Just keep your temps under control, and you'll be fine.

Last edited by Joe24; 03-23-2022 at 05:59 PM..
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Old 03-29-2022, 03:54 AM   #31
somes2121
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Default Re: BGA reballing techniques and equipment

Hi all! Can somebody tell me the tempreature settings or profile settings for nvidia gpu`s? i use Honton HT-R490 but i dont know the tempreature curve. Thank you!
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Old 04-01-2022, 12:46 AM   #32
Joe24
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Default Re: BGA reballing techniques and equipment

@somes2121: You mean for reballing, or for installing the GPU? Don't think there really is a "proper" profile that matters for reballing. You're just heating things up until the solder balls melt into place, and no more. Don't use higher temperatures than you need, or for longer than you need to.

As far as installation goes, that's a bit more involved if you want a reliable result. Nvidia's/AMD's factory spec will be locked in a dark vault somewhere. Doesn't matter, the idea is the same for all reflow soldering.

Everything (board, chip) needs to be heat-soaked for a few minutes using a bottom heater. I'm not a fan of the "hot-plate" style heaters like the Honton, I prefer the non-contact infrared (barbecue/grill style) type. Opinions on preheat temperature vary between 100 - 170 C+, even among industry professionals, and it also depends on your heat source how long the board takes to get up to temp. Just don't heat things up too fast (it should take minutes, not seconds), and at this point keep everything below the melting point of your solder. By 'heat-soaked', I mean everything must be that temperature all the way through, not just on the surface.

Then once you're done your preheat with your bottom heater, you add top heat to raise the GPU and the solder joints under it to a few degrees past the melting point of the solder you're using. Again, opinions vary as to specifics, and so do the melting temps of various solder compounds. For example, if using a leadfree solder which melts at 237C, you might need the chip/board-pads/solder to reach 250C or so peak (not 1200C) to ensure the colder spots receive sufficient heat. This main heating step happens fairly quickly compared to preheating, and you shouldn't keep the solder molten for more than 20-30 seconds total. BGA chips are designed to withstand soldering temps for about that length of time, but no longer. Make sure you heat the entire chip evenly, especially with larger chips, otherwise one corner will melt before everything else, that corner of the chip will drop mashing the solder balls together on that corner and you'll have to start over. Don't use hotter temps than you need, or you can fry chips or brown the circuit board.

Then let everything cool gently down to your preheat temperature (100-odd C). This is important to do slowly (minutes), otherwise you'll get stress cracks in the solder joints, or at least weaknesses that could lead to future failure. Just turning the heating elements off on your bottom preheater and letting the board coast down to temp is fine.

Once your board has gently cooled down to 100C or so, you may cool it quicker from that point if you're in a hurry. In normal use the board is often heated and cooled rapidly in the 20-90C range, so it should be able to handle it.

Another important note is to keep the board dead flat throughout the procedure. If you have a long heavy card, don't just support it at the far ends. A small amount of bow in the board is a lot when you consider that the GPU sits maybe 0.3-0.4 mm above the surface. If the board is bowed, the solder balls in the center of a very large chip might not even be touching the board, and the ones at the edges of the chip will be smushed together and shorting out.

Opinions will vary, and I'm sure some will disagree with me about specifics. As mentioned, there are arguments even within the industry about whose way is better, whether to use more top than bottom heat, vice versa, etc. However, those are the broad strokes.

Last edited by Joe24; 04-01-2022 at 01:27 AM..
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