Connecting unconnected BGA ball

[Ice-Tea]

Colleague of mine has a bit of an issue (we've all been there, haven't we...) where a line was connected to a GPIO and should have been connected to a dedicated line...

6-layer board
0.8mm BGA
4 layers GNd and 1 layer 3V3 to get to the ball

So, is any company at all on this planet that could get to this ball and connect it? Money is, within reason, not an issue.

Actually, never mind the 'within reason' part...

Thoughts?

[jmelson]

Seems that if you drilled a hole from the underside of the board, you could remove the BGA pad.  Careful cleaning of the hole wall should eliminate any shorts.  Then, a thin pin with a teflon sleeve could be poked into the hole and soldered to the device ball.

Yes, this is all microsurgery, but if it is just one unit to test that the device and rest of the board works, it ought to be doable.

Of course, there is the possibility there are inner-layer traces right at that spot that you'd end up drilling through, so that could wreck the whole idea.

Jon

[Ice-Tea]

Sounds about what I need... ever seen it done? Know of a company that does this in the EU? Found these guys in the US:

http://www.circuitmedic.com/guides/6-2-2.shtml

pretty much what you are describing...

[AndyC_772]

I've had this done. In my case it was a floating input which needed to be connected to something (I forget what) in order for a CPU to boot.

The company that did the job was Surface Technology International. They removed the CPU, attached a tiny wire to the top side of the PCB in between the BGA balls with a bare end making contact with the floating pin, then fitted a new CPU with the wire in place. Amazing rework, and it worked first time.

That was 10 years ago, and IIRC it was a 1mm pitch device.

http://www.sti-limited.com/

[Ash]

It occurred to me that perhaps you could make a small "Adapter" PCB. This is probably a crazy idea and I certainly have not done it.. 

Basically make a 2 or 4 layer board using a quick turn around supplier that essentially has the BGA footprint top and bottom, with most of the pads just dropping straight through, but re-routing the erroneous nets.

Not entirely sure how to attach "balls" to be bottom, but perhaps you could use a solder mask defined pad, and stencil on the balls like you do when repairing BGAs.. You'd obviously have to remove the existing device, and re-mount it onto the adaptor..

like I said - probably a crazy idea 

Ash.

[Ice-Tea]

Crazy... but not stupid. You could probably "ball" it like you said.. Doubt I'd get it the first time right, though. So, food for thought for another time, but not quite now...

[helius]

What you are calling "adapter PCB" is typically called an interposer in the industry. One consideration is that you may want the chip-to-interposer solder connection to not reflow when the interposer is mounted to the board, so a higher melting point solder may be specified.

[Ice-Tea]

I've had this done. In my case it was a floating input which needed to be connected to something (I forget what) in order for a CPU to boot.

The company that did the job was Surface Technology International. They removed the CPU, attached a tiny wire to the top side of the PCB in between the BGA balls with a bare end making contact with the floating pin, then fitted a new CPU with the wire in place. Amazing rework, and it worked first time.

That was 10 years ago, and IIRC it was a 1mm pitch device.

http://www.sti-limited.com/

Missed this. Thanks for the input!

[jedas]

We have a guy who can do this. Last year we had to connect wire to XC6SLX9-2CSG225I ball. 255 ball 0.8 mm package. Everything worked fine.

stgedas eta gmail.com

[Ice-Tea]

To anyone that cares or stumbles on this thread later on: we ended up sending the boards to Across which in essence is an outpost of Retronix in Scotland.

Thanks all for the input!