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Old 07-12-2022, 03:11 PM   #1
ugamazing
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Default Procedural question about BGA rework and removal of CPUs

I have been working to develop a consistent and reliable method/workflow for removing, re-balling, and replacing CPUs on various MacBook Pro models (2015-2020).

I have done OK so far, but there's one detail I need to sort out. I'm hoping someone much more experienced than myself may be able to shed some light:

I am noticing the pulled CPUs (to be re-balled) come off fine, and they "look" fine as well, immediately when I pull them. However, within a few minutes, after cooling, the CPU chips develop a very, very slight curve/bend. It's SO SLIGHT, maybe a 1-2% arc, but it's there, and it causes issues. I actually only noticed the bend because I kept getting solder paste under the center ball areas only when re-balling. I thought my stencil was lifting a tad, but I then realized the chips themselves are slightly curved and not flat, causing the stencil to not sit flat. Bummer.

I'm not sure if the bending/buckling is being caused by too much (top/bottom) heat; heating too quickly; cooling too quickly, or because I'm not preheating the boards in any way (moisture problem??).

I suspected first that the CPUs were possibly cooling too quickly (since they look perfect when I actually pull them), so I tried to lay the pulled CPU back on the board for the cool-down process (~5 minutes), but it didn't help; the chips still have a slight warp.

Then I suspected I may need to bake or preheat the boards a bit before I pull the CPUs. I do use a generic profile on my BGA station, and it takes about 8 minutes from start-to-finish when pulling them, but I'm wondering if I need to heat the boards up even more slowly? Is 8 minutes too quick?

I have a preheater I'm going to try to incorporate, but my other question is: What would be the best use of the preheater in this situation? Should I preheat the boards slowly for an hour or so to "dry them out" (sic), or should I be preheating them for 10-20 minutes to bring them up to temperature even more slowly than the BGA station would? Obviously, it would be ideal to just use the BGA station preheater, but it's pretty confusing to use already (cheap $1,200 Honton HT-R490 station), and I can't figure out for the life of me how to run *ONLY* the preheater. Documentation for this unit is nearly impossible to read. It seems I must run an actual profile, and I don't seem to be able to select only zone 3 (IR preheater).

Any help would be appreciated. I have tons of parts boards to practice on, but I've pulled around 10 (dead) CPUs so far and wanted to get some input before I continued with my own trial/error. I can't move onto learning the re-ball process until I can get a good CPU to start with.

Last edited by ugamazing; 07-12-2022 at 03:19 PM..
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Old 07-12-2022, 04:51 PM   #2
ugamazing
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Default Re: Procedural question about BGA rework and removal of CPUs

OK, so I figured out how to better modify profiles on this thing. I was able to find a manual for a very similar station (different screen/display and input methods, which was what stumped me).

Does anyone have any good BGA profiles for the 2015+ CPUs? I'll play around with the profiles more tonight and test them a bit more. I'm modifying them to preheat a bit slower right now.
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Old 07-15-2022, 02:18 AM   #3
MobyDik13
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Default Re: Procedural question about BGA rework and removal of CPUs

Dear friend. My name is Vitaly. It is necessary to make or buy a frame along the contour of the processor from metal (separately for each type of processor.) Before soldering, install a metal frame along the processor frame and glue it with a UV mask or any other easily removable glue that is not afraid of strong heat. After desoldering, the frame will give a stiffener and the processor will not bend. Then we remove the frame. This applies to any other large chips and some intel combo processors. I asked the frame to be made at the factory of my friend and saw it on aliexpress. In theory, it can be made by yourself with an electric cut and file. It looks like in the photo.
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Old 07-16-2022, 08:39 AM   #4
ugamazing
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Default Re: Procedural question about BGA rework and removal of CPUs

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Originally Posted by MobyDik13 View Post
Dear friend. My name is Vitaly. It is necessary to make or buy a frame along the contour of the processor from metal (separately for each type of processor.) Before soldering, install a metal frame along the processor frame and glue it with a UV mask or any other easily removable glue that is not afraid of strong heat. After desoldering, the frame will give a stiffener and the processor will not bend. Then we remove the frame. This applies to any other large chips and some intel combo processors. I asked the frame to be made at the factory of my friend and saw it on aliexpress. In theory, it can be made by yourself with an electric cut and file. It looks like in the photo.
Wow thank you so much! I will look into this ASAP and try this--thank you again!

Also, I've now began removing them without the BGA machine, and using our preheater only. It is working well, but still have bends, despite pulling the CPU immediately when it desolders. I'm hopeful the frame will assist with the issue!! Thank you!
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Old 07-22-2022, 08:12 AM   #5
ugamazing
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Default Re: Procedural question about BGA rework and removal of CPUs

OK, I think I may have identified part of our issue. Our humidity here is VERY HIGH--over 90% for a few months consecutively (unlike many other areas of the earth). I had not considered this to be a big issue until just now, and have implemented a baking step into our desoldering process. I did a lot of reading on PCB heat/CTE issues, and all of our current methods are correct and refined, so I do not suspect it's a heat/time issue causing the bend. I suspect moisture is in fact the culprit at this point.

Now, we will be baking all PCBs at 120C for ~6-8 hours before desoldering CPU. I had been wondering if some tiny amount of moisture may be causing the minor warping issues we're experiencing, so I spoke with a contact in China who pulls CPUs to sell, and they mentioned humidity could be a very big problem if our PCBs are not stored in a sealed state (they are not).

I am also working right now with a CNC/stencil company to produce some aluminum braces/frames for CPUs to test out as well. Have to wait for them to produce samples first, and will take some time. So trying the bake process while we wait!
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Old 07-15-2023, 05:17 PM   #6
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Default Re: Procedural question about BGA rework and removal of CPUs

Quote:
Originally Posted by ugamazing View Post
OK, so I figured out how to better modify profiles on this thing. I was able to find a manual for a very similar station (different screen/display and input methods, which was what stumped me).

Does anyone have any good BGA profiles for the 2015+ CPUs? I'll play around with the profiles more tonight and test them a bit more. I'm modifying them to preheat a bit slower right now.
Hi, I have this machine and I am in the same predicament as you were. Please can you share where to get decent information how to use this thing HT-R490. I have searched everywhere and cannot seem to find information how to adjust and change profile. I am having difficulties how to adjust the profile when running one and how to make adjustment on the go or as required when running a profile. Please advise thank you.
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