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Reflow Bga chip.

Discussion in 'General Electronics Discussion' started by Tha fios agaibh, Dec 24, 2018.

  1. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    I picked up a nearby scrap plasma TV for a few bucks with a pink and green pixelated screen.
    I found the graphics processor, added a little flux around its edges and heated it up in a circular motion with my hot air gun......and voila' , it fixed the problem,
    but I realize this is likely just a temporary fix. (I don't have a reflow station to do a proper fix.)

    The backside of the board is loaded with tiny smd components directly behind the chip. How is a proper removal/reflow of a bga chip accomplished without the other components falling off from the bottom?

    Is it just the surface tension that holds the component in place once the solder melts, or is the temp applied to the bottom is just under the melting point?

    Idk if I'm up to the challenge of doing a proper fix on it due to my lack of experience and equipment. I'm just curious how its done with components on the backside.

    Thanks and Happy holidays.
     
  2. Bluejets

    Bluejets

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    Oct 5, 2014
    Thought about this a couple of times also.
    Apparently the surface tension is enough if the process is done similar to the youtube video.

     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    It is also possible to do this with 2 solders having different melting points, or simply gluing the components on one side (typically the bottom side :))
     
  4. BobK

    BobK

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    Just to lighten things up — use an anti-gravity field.

    Bob
     
  5. Tha fios agaibh

    Tha fios agaibh

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    Ok thanks, but what about reworking existing chips?
    Heres my gba graphics chip with hundreds of tiny balls of solder under it. (only slightly bigger than 1") 2018-12-25 11.13.45.png
    To properly reflow the balls of solder under it, I assume I would need to heat the underside (with more smd components) to an accurate temperature at or just under the solder melting point while also heating the top side to remove the chip. Then the surface would need to be cleaned and then reballed with solder.

    I'm not sure an improvised alternative to a reflow oven, like a toaster oven, space heater or a halogen lamp would be accurate enough to facilitate such a delicate operation. Would it?

    If the under side temp was too high I could see this ending in disaster by someone clumsy like me knocking components off of the underside if trying to move board from the oven.

    I guess what I'm asking is; Is there a better alternative to quasi-fixing this chip than just heating with flux like I did?
    How do you determine the fault is the chip itself rather than the solder connections under it?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Ah, now I see what you're asking.

    There are heaters for the bottom of boards. They blow hot air over the bottom of the board to pre-heat the board. The temperature of this air is below the melting point of solder. The idea is to reduce the temperature differential across the board.

    This does at least 2 things:
    1. Reduces thermal stresses across the board
    2. Makes it far easier to heat the other side of the board to a temperature which will melt solder
     
    Tha fios agaibh likes this.
  7. Cannonball

    Cannonball

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    If it isn't broke don't fix it. If it needs fixing use a hot air bonder and they aren't cheap.
     
  8. Tha fios agaibh

    Tha fios agaibh

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    Yes, I'll leave it for now as the tv is working great.
    I'm thinking if I attempt to replace
    Yes, I'm not going to spend $3k on a dedicated oven, but I may attempt a jury rig inexpensive heater set-up with a temp probe attached to monitor the heat. I don't do enough of these types of repairs to justify the costs.

    Tv is working great,.....so far.
     
  9. Cannonball

    Cannonball

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    That is great. I wouldn't worry about the solder joints around the chips unless you have trouble with them. They are soldered pretty well at the factory with a hot air bonder.

    To replace some of these chips without a hot air bonder might be cheaper to replace the whole board.
     
  10. Tha fios agaibh

    Tha fios agaibh

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    It's my understanding that the solder balls under the chip often fail after a while from expansion/contraction during heat/cool cycles of the chip. I don't know if my heating up the top of the chip with hot air fixed a fractured solder point, or something internal in the chip?

    I've looked online for replacement boards but they are not available. For about the same price ($100), I can have it reballed which is said to fix the problem, but only has a 90 day warranty. Doesn't seem worth it if it can crap-out in 90days

    Who knows, my quick fix may even last a year or more?

    I prefer the types of repairs when you find and replace obvious failed components, rather than a "I think it's fixed" scenario.
     
  11. Cannonball

    Cannonball

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    I have worked with Motorola chips before I retired. Those chips are very reliable. It is very unlikely for them to fail.

    I would wait until it fails before I would do anything else to it.
     
    (*steve*) likes this.
  12. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Thanks, I appreciate your advice/opinions.
     
  13. Tha fios agaibh

    Tha fios agaibh

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    Update: Picture still working ok, but all my Hdmi inputs just quit working.:(

    I believe the hdmi inputs are switched through another chip before being sent to the graphics chip I reflowed last month.
     
  14. Tha fios agaibh

    Tha fios agaibh

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    Update:
    I got 8 months use out of it.
    But the Tv just died again, and I'm back to a pink/green screen.:(

    I guess I'll try and reflow the chip again with my hot air gun and see if it does anything.

    Is there a recommend heat range I should try?
     
    Last edited: Aug 22, 2019
  15. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Why doesn't my post showing up under "new posts"?
     
  16. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    I reflowed the gba graphics chip (again) at 370c.
    Tv is back to working again although I'm not sure I'm confident enough to hang it back on the wall. (heavy plasma)

    Who knows if I'll get another 9months out of it or not.
     
  17. bushtech

    bushtech

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    Well done, glad it's working again.
     
  18. Tha fios agaibh

    Tha fios agaibh

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    Aug 11, 2014
    Thanks bushtech. I'll take it as a success, even if its just a quasi- fix.
     
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