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drunkenninja

BGA Pad Reconstruction / Repair - Motherboard

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This is one of the guides I created some years ago I would like to share, hope it helps some of you guys out interested in rework/motherboard repair. (I have updated it quite a bit)

 

I got frustrated the a couple of weeks ago during a clean-up and managed to lift a pad off the board, I threw it in the "bored pile" cause I was determined to correct my error one day.

 

I found later looking at the GPU that one corner's solder balls were intact, and the lift must have weakened the pads under the solid solder balls, I was heartened "sort of" that my cleanup method wasn't to blame.

A total of 3 pads were lifted after cleaning the board fully, all in the same region.  :geek:

 

Quote

 

TIP  :frantics: 

If the pad's traces go nowhere it is likely a dummy pad, (check Board Schematics) you can normally tell these as under the pad it will be a dull grey, and on top it will have no trace or via next to it, many pads on the board are simply GND or Test points, so there is a good ratio of a pad not being needed, also in my experience dummy pads lift much easier than active ones. If you lift an inactive pad just leave the solderball off of the GPU and re-attach as normal.

 

 

Ok, onto the repair, here are some items your gonna need, most you will likely have already:

 

Quote

Soldering station
(Unleaded) solder
Solder wick/braid
Fibreglass pen (If you don't have this you can use an exacto knife or razor but the fibreclass pen is by far the best and safest)
Liquid flux, preferably INSAT
Paste Flux
A magnifying glass (must have high powered magnifying range) or microscope.
Solder Mask
Toothpick (for applying flux paste and solder mask)


IMPORTANT 


This is just my technique to do this repair, and it works great for me, I'm not saying it's the best method, this is not an easy repair and definitely not for a novice, as a minimum I would say you need some standard trace repair experience either using bridged solder or preferably using low gauge kynar wire. I have tried to make it as easy as possible though and it's definitely worth a try if your in a bind.

 

The traces from the GPU are incredibly close together, this is why we are using braid/wick copper wire and a high powered magnifying glass

 

Ok so lets move on.

 

So the first thing you want to do is get your braid and dissect it a little, the easiest way i found was to pull each side and it it will begin to unravel. what we want  are those single strands of the braid, once you have some you want to put some flux paste on them and tin with your unleaded solder.
 

Quote

 

TIP  :frantics:

you could pick up a ball of unleaded solder with the entire wick and unravel the individual wires while it's still hot - its another option that pre-tin's the wick

 

 

Now you want to clean up your board with IPA or thinner, I pretty much use standard thinner for everything these days but each to their own. once it's all clean you will want to expose the copper traces, of the points you want to solder from, you will do this with your fibreglass pen, exacto knife or razor. (see below).

 

SEE  IMAGE LIFTED PAD 001

 

Clean the board up again.

 

You now want to tin your traces, with unleaded solder, the easiest way to do this is run your wick and some flux over the trace, you will find that a thin layer of solder will be attracted to the traces, just what we need.

Now get your insat and rub it over the tinned traces with a brush, wait a few minutes for it to get sticky, now you really need that magnifying glass, position the tinned wire on the trace with some tweezers, it should stick nicely cause of the INSAT, you want the wire going right into the pad area, it should reach one side of the pad fully to the opposite side of the pad (but no more).

 

Again using your magnifying glass gently tap along the wire at 1 second intervals from one end to the other (depending how long your trace needs to be, any size is fine actually), feel free to use a pair of tweezers to support the wire also and keep in mind that it might only take one tap to flow the wire to the trace, don't hold the iron on the trace cause you could sever it.

 

Finally test the continuity of the new points with a DMM, use the two furthest points of the exposed trace to confirm you did a good job.

Gently clean up the area, use Thinner then IPA or just IPA this time.

 

SEE  IMAGE LIFTED PAD 002


I actually redid the point closest to the bottom of the site as I was not happy that the wire did not fully cover the pad - forgot to photograph though

 

Use a toothpick and some solder mask to tidy up the exposed parts of the board.

 

The reason we used unleaded solder is cause you will put a leaded GPU back on the board, the unleaded solder will stand firm at 190C meaning the solder ball will flow straight onto the trace wire you just created.  :thumbsup:

 

A word of caution, although your joints should be relatively solid, be aware not to mess around too much with the seating of the GPU before reflowing to the board, remember that the unleaded solder balls will automatically shift the GPU to its correct position in reflow state if your not exact.

 

I am not a big fan of the wire glues in the market, I tried them in the past on damaged pads I found they didn't hold upto the temps, plus I'm always wary of using glues on PCB's to form circuits. Maybe there are better ones now? I also heard of copper tape being used (the scaletrix type but again I would be worried about how adhesive would react at 190C but I'm happy with using unleaded solder as I know it will form as good a connection as you will get and be solid at leaded reflow temps.

 

Another option to consider, and you can incorporate this into the above guide if you like is to place a small amount of solder in the pad and then heat with a a hot air wand, it should naturally be attracted to the small trace repair you did, but these are all just ideas, you can play with.

 

Apologies for the pics, getting pcs of those tiny points is tough, if you open them and zoom in, you can see the points relatively clearly though...  

 

lifted_pad_001.jpg

lifted_pad_002.jpg

Edited by drunkenninja
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Two years ago I found I very useful tool for this process.Its name is CS FLUX and you can check some very useful tutorials in the youtube.One that I recommend you to watch has the name ''CS-FLUX application instructions for GPU removal or reflow''

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