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.
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.
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