Saturday, June 6, 2015

Reballing adventures - part 1

Some time ago I wrote about a reflow I did on a broken laptop:
http://hackcorrelation.blogspot.de/2014/01/medion-md97900-laptop-teardown-and.html

The unit worked fine for ~6 months, after which it failed again with the same symptom: no video.
It sat unused for one year but then I received a PS3 with the YLOD symptom. This prompted me to order a BGA reballing set from eBay and attempt to fix them both.

The PS3 reball will be in a part 2 of this series.
This is not a guide, just a journal describing the mistakes I've made during the process.

The video chip is the plagued NF-G6150 , also used in the HP DV6000. The laptop still has decent performance when paired with an SSD, for today's standards.


The area around the chip was masked with Kapton tape:


Then 'shielded' with food-grade aluminium:


I had a goose-neck-style phone cradle sitting around which provided a stable hands-free holder for the hot-air gun.


The chip was painted with a black marker (for reducing thermal reflection) and the measurement from an IR thermometer was compared to a K-type probe.


The hot air gun was left at 100C for around 15 minutes in order to heat the board uniformly to avoid a sudden thermal expansion on the working area.


After which the temperature was raised to ~350C on the gun (~250C on the chip), air speed was set to 3-4 (out of 7). This enabled a clean removal of the chip, but you can already see the non-uniformity on the surface pointing to a delamination.


The chip and motherboard were cleaned from solder - there are hundreds of how-to videos on YouTube.
The basic process: flux is added then the soldering iron is run with some fresh solder on the pads. After most of the solder has been removed, some more flux is added and the remaining solder is removed with a [copper] wire braid. The flux residue is cleaned with alcohol.





Did I mention how much I hate the Blogger editing interface? There's no way to align multiple pictures into the same area.

The chip is then covered in flux and the reballing pattern is placed over it.


A nice trick for getting the balls in (hehe) is to pour from the ball container into a larger container, over the pattern. Instead of the ~200 balls you will be using ~3k, but they can safely be reused afterwards. Learned this trick on YouTube from some random Indian guy:


The pattern and chip are then heated in order to reflow the balls and attach them to the chip


First attempt: 20% of the balls got detached from the chip and stuck on the template. Do not reuse these ones!


Second attempt: only two balls detached. They were manually placed on the pads and reflowed again, without the template in place.


The result looks promising:


Time to reflow the chip back into place. The black stuff is permanent marker that I've used to increase emissivity(?) or reduce heat reflection.


Result: no video.

I've tried two or three times to reflow the chip, I think I might've also reballed it again but there was no improvement. This one goes back to the scrap pile.

3 comments:

  1. even if you did it perfectly there was very slim chance it would of worked

    its not the balls under the chip that go bad, its the balls that hold silicon die (shiny rectangle) to the bga carrier (green rectangle with decoupling caps)

    heating the GPU itself temporarily fixes connections to the die, reballing is just a red herring
    http://www.youtube.com/watch?v=1AcEt073Uds

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    Replies
    1. I don't agree 100% with the video but there is a lot of truth in that. Flip-chip bonding, once completed, is able to sustain higher temperatures (>300C) than the ones used in bonding (100-300C).

      In my limited experience (>10 reflows) the success rate is 20% and the long-term failure rate is 100%. That should be the real take-away.

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    2. explanation in Russian (great channel, even if you dont know the language)
      https://www.youtube.com/watch?v=VjmBv6nvUOM

      http://www.theinquirer.net/inquirer/news/1050052/nvidia-chips-underfill

      Nvidia did a big recall, chips past 2010 are supposedly 'fixed', although they still fail just as often. Apple was forced to do 3 recalls afaik :D

      problem is in the stuff between die and carrier (glue/underfill). It changes shape permanently with time and repeated thermal cycles cracking and lifting balls off pads. Heating whole gpu to 150C with no heatsink for a few minutes relieves stresses in the material and fixes balls back into place .. for few days/weeks/months (depending on thermal stresses).

      Only "permanent" (newer nvidia chips seem to last 2-3 years) is brand new gpu, and those are >$50, often more than whole machine :/

      Xbox is another story, M$ effed up and designed bad thermal environment for the gpu, whole pcb bends under repeated thermal stress.

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