Saturday, June 6, 2015

Reballing adventures - part 2

Thinking that I've had the process in hand, I've tried reballing a PS3 video chip. I'm not sure it was the video chip at fault since the person who gave it to me had attempted a reflow on it, transforming the YLOD (yellow light of death) into a GLOD (green one).

Setup was pretty similar to the one in the previous post; started with a light warming (100-120C) of the complete board to provide uniform thermal expansion and remove moisture:


However the chip proved to be a beast and my hot air gun was raising the temperature too slowly to be safe.

 I began looking for items that are a similar size and shape in order to make a template for the gun. This screwdriver accessory proved to be the best match.


The layout was started by wrapping some gardening wire around the magnetizer and holding it in place with some masking tape.

Not removing the tape proved to be a mistake when temperatures of 400C were involved.
The wired frame was then wrapped in food-grade aluminium foil...
...and after preheating the board I started following the lead-free solder temperature profile.
The attachment had to be moved really close to the board in order to get the temperatures to rise up fast enough: around 3 minutes are required.
Any longer than that and the chip can become toast, as well as the parts around it.

I tried to get the chip to be at 240C but it would not move. I've then removed the heat spreader (top aluminium part) exposing the bare chip and tried to remove that.

I was working in 3-5 minutes increments then slowly removing heat as to not stress the parts, then started a new cycle with 10C more.
After around 5 cycles of the above I raised the hot air temperature from 350C to 420C and see where that might go.

Still no luck, tried various tools to pry the chip off while still hot, thinking it might be attached with some strong glue.
Found out the hard way that the required temperature for removal was much higher, measured around 265C until solder balls started popping off and 280C until the chip could be removed.
Oh, I had to use a paint stripper for this, the hot air gun just could not provide sufficient thermal flow.

The result is ghastly:


The chip was permanently bent by the tools used to try to pry it, pads were ripped from the chip and pads and tracks were ripped from the motherboard.


I did not even attempt a reball at this point, there's no coming back to life for this unit.

Lessons learned:

  • have the proper attachment for the heat gun
  • ensure the gun can reach temperature in a safe time - or replace it if not
  • do not try to pry the chip - minor nudging should be enough to see if it's removable
  • most glues soften by the time the solder is molten
  • improper heating patterns (insufficient preheating) leads to delamination
  • same as above with regard to moisture content
  • eyeballing the temperature works much better in my case than using tools
  • prepare the full workflow in advance and work fast
I can see why reballing is such a lucrative (or rather expensive) service: the guys (and girls?) doing this have to break tens of units in order to teach themselves the proper process.

However, not everything is lost: I'm pretty confident now that I can prototype with BGAs with a 20% success rate. i.e.: 'Bad experience, F--, would attempt again'.

3 comments:

  1. looks like pcb soaked all the heat
    you still have cpu on this board for experimentation :) this time setup second heat gun under the pcb at ~100-150C

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    1. I forgot to mention that the boards were heated from the underside , just that in this case the chip was much much harder to remove. Would have been nice to experiment if the unit actually booted up, otherwise there's no way of knowing if a reflow/reball is successful.

      I'm looking forward to see if people were able to successfully reball large chips (>16 sq. cm.) using the Aoyue 858D+ and similar clones. For me it's a failure.

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    2. googled out of curiosity and bam: http://www.ixtreme.net/repair-section/39085-reflowing-profiles.html :o

      Got 858D myself ("baku" branded), would not attempt reballing without preheater and few thermocouples covered in flux fixed to chip, pcb next to chip and pcb under the chip. Gun goes to 450C and eats ~700W so there is no power shortage, just needs better process control.

      I say go for the cpu on that xbox board, if anything just to get a feel for when balls are really melted. I destroyed maybe 10 random garbage pile laptop boards and graphic cards before getting a hang of rework station, did everything from ripped pads to charred chips :).

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