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BGA rework with unplugged vias PCB

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#46043

BGA rework with unplugged vias PCB | 7 December, 2006

As you are aware the common method to rework BGA is : 1. Remove BGA with hot air reflow machine ( SRT as current practice) 2. Clean the BGA pad using solder iron and solder wick. 3. Replace BGA with SRT rework machine.

The problem we have with unplug via is when we clean the BGA pad, the solder resist cover the trace between pads and vias will be removed. During the solder removal process certain amount of solder will also get into the unplug vias as well. During BGA replacement process, two thing will happen. First, due to vias plug with solder, explosion might happen and cause solder short or open. Second, due to the solder resist has been removed, the solder from BGA ball will flow into the vias and caused insufficient or unsolder BGA balls.

I would like to hear any one have any process that could take care of such problem.

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jimby

#46055

BGA rework with unplugged vias PCB | 7 December, 2006

We have our circuit board vendor put a solder mask dot over the vias after HASL process. It's a little more expensive but eliminates the problem that you are talking about.

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RDR

#46061

BGA rework with unplugged vias PCB | 7 December, 2006

You have two options

1. Get some real solder mask form board supplier (not touchup pens) and repaint the trace and heat cure.

2. Fill the via with solder before reflowing new part, this usually works but sometimes it doesn't.

We use Method 1

Russ

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#46076

BGA rework with unplugged vias PCB | 7 December, 2006

When rushing to get a job done, it's easy to accidently remove solder mask from a nearby via when dressing BGA pads after removing the part. Just hit the via with some super glue [then say a small prayer] and push on.

As an alternative, look here: http://www.circuittechctr.com/guides/2-4-3.shtml

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RDR

#46100

BGA rework with unplugged vias PCB | 8 December, 2006

Good idea Dave F!! never thought of superglue to cap off the via, easier than remasking and curing for sure

Russ

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#46338

BGA rework with unplugged vias PCB | 21 December, 2006

The problem with super glue is that is has a cyanide base that turns into a toxic gas and evaporates when heated.

See IPC-7095. Via's should be fully plugged with solder mask at the fab house. If your PCB designers are not up to speed on IPC requirements then you can plug with circuit board slder mask. Touch up pens are no good.

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#46348

BGA rework with unplugged vias PCB | 21 December, 2006

Dennis

We know that cyanoacrylates are flammable and breathing hazard before curing, but are unaware that the cured adhesive had those properties also. Can you give us documentation of that fact?

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