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I am facing problem in a 16-bit transceiver chip, 74LVCHR16245AZQLR, which is a 56-pin BGA package.

Its one data pin is not working as expected while all other pins are working OK. The problem pin is only sinking 6 mA of current while all other data pins, which are working OK, are sinking 12 mA of current.

I suspect it is a dry-soldering issue. But I don't how to fix this as the chip package is a 56-pin BGA. Is there an easy way to fix this?

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    \$\begingroup\$ you could try putting it through the reflow process again to melt the solder balls again and hope it helps. Other than that: unsolder, clean contacts on both sides thoroughly, re-ball, re-solder. What were you expecting? \$\endgroup\$
    – Marcus Müller
    Commented Jun 24, 2019 at 6:52
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    \$\begingroup\$ Easy is not a word typically associated with BGAs. \$\endgroup\$
    – user98663
    Commented Jun 24, 2019 at 6:54
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    \$\begingroup\$ Unless you're a masochist, your only real option is to try either reheating the whole chip or at the least the area around the dud pin. If that doesn't work, replacing the whole thing is the only 'easy' option left. \$\endgroup\$
    – hekete
    Commented Jun 24, 2019 at 8:25
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    \$\begingroup\$ Put a weight on it and reflow the solder. If that does not help, it's de soldering, reballing and try again. Plenty of guides on youtube. \$\endgroup\$
    – winny
    Commented Jun 24, 2019 at 8:44
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    \$\begingroup\$ @winny It worked.. I put little weight on the edge where the pin was located and slow air reflow that point and it did the magic. \$\endgroup\$
    – alt-rose
    Commented Jun 24, 2019 at 10:07

2 Answers 2

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For cold or dry solders on BGAs, you are working blind without X-ray or just functional testing like yours, so it's not easy for sure.

First order of business would be to reflow the BGA with hot air. There are plenty of YouTube videos of GPUs being fixed this way in your home oven with some care. Reflow

If this does not help and it's your one-off board and not mass production you are trying to solve, I would proceed to step two by putting a weight on the BGA. This will most likely violate IPC but allows for a too small solder ball to bridge a connection (by Z-axis movement).

If this still does not help and you are not interested in reballing the BGA (below), consider bumping the board while hot. Highly inadvisable otherwise, but if you are about to throw away the board anyway, this has been known to bridge the missing connection (by X- and Y-axis movement). I have witnessed a street vendor in Hong Kong who repaired iPhones and resoldered BGAs with this method by tapping it with his tweezer while the solder was flowing and letting the capillary forces re-center it after bridging whatever was not connected. Fascinating!

Last resort, reball. Reball

Lastly, a bit of inspiration for your next BGA project: BGA-wire

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    \$\begingroup\$ As promised, +1 from me. Good step-by-step ideas! \$\endgroup\$
    – MCG
    Commented Jun 24, 2019 at 14:22
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    \$\begingroup\$ Last picture: Someone must have been ... meticulous! \$\endgroup\$
    – Peter Mortensen
    Commented Jun 24, 2019 at 15:58
  • \$\begingroup\$ @PeterMortensen that last picture gives me nightmares! Imagine realising you mid-sized a few connections! \$\endgroup\$
    – MCG
    Commented Jun 24, 2019 at 17:38
  • \$\begingroup\$ If you are using a contract manufacturer for assembly, they will likely be able to rework BGA for you, typically this is at relatively large cost for mass production, but if it is a critical prototype its $30-$50 a piece in my experience, it is cheaper because they already have the fixturing if they are producing your boards. . There are commercial companies that will rework BGA for $100-$200 a board , which may be worth it if the board is irreplaceable otherwise. Where there is a will there is a way, Even wire jumpers to inner layers are doable. \$\endgroup\$
    – crasic
    Commented Jun 24, 2019 at 18:55
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    \$\begingroup\$ @MCG A fellow EE student and friend did a radio rely project on a breadboard (the logic, not the RF) using only red wire. A few hundred of them. Anyone but him was clueless when a wire came loose in the field. Good times! \$\endgroup\$
    – winny
    Commented Jun 24, 2019 at 20:41
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Unfortunately, BGA is not easy to rework. You could try reflowing again, or if you happen to have a via by the pin, shove a bit of flux there and heat with a hot air gun.

If that doesn't work you have 1 of 2 options. You can either scrap the board and use a new one, or you can remove the IC, clean all of the pads, then you will have to re-ball the IC. This is not an easy process though I'm afraid.

If I were you, I'd just move on to a different PCB, it may end up cheaper than re-working this one.

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    \$\begingroup\$ I'll point out that for inexpensive and readily available parts, it may be cheaper and easier to pitch the desoldered BGA and use a new one. Mouser lists this particular part as $2.51, which is probably cheaper than reballing it. \$\endgroup\$
    – W5VO
    Commented Jun 24, 2019 at 15:40
  • \$\begingroup\$ @W5VO very good point. I was trying to go for more of a general approach, but yes, that's a very valid point! \$\endgroup\$
    – MCG
    Commented Jun 24, 2019 at 17:37

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