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Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Reworking BGA's

Views: 3906

#65073

Reworking BGA's | 21 September, 2011

I would like some input on reworking BGA's and the best method. I have reworked BGA's since 1998 using both micro stencils and just flux dipping the parts. I have reworked SN/PB and lead-free (AIM NC258) BGA's for the last 8 yrs. with just flux. I have not purchased one of those micro stencils in years. I started working at a new place about 3 months ago and here they are reworking BGA's with micro stencils. Is there any positives of using a mini stencil over just flux dipping? I'm told it is necessary and it is the way they have been trained to do it. I personally feel it is a pain in the arse and unjustified since flux dipping works just fine. Any input is greatly apprecieated.

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#65074

Reworking BGA's | 22 September, 2011

A lot of views and no input??

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#65075

Reworking BGA's | 22 September, 2011

We agree with you.

Recognize that these new solder connections have less metal and a lower standoff than similar BGA solder connections that have not been reworked. This could reduce the reliability of your product, somewhat.

Flux or gel may be used on boards for rework as there is already a coating of solder left from the removal process. They should not be used on copper or gold board for prototype assembly.

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#65076

Reworking BGA's | 22 September, 2011

Dave has stated the caveats well.

I too have similar experience in reworking BGAs that mirrors your own.

The only situation where I saw this as an issue, was in memory devices where a row of BGAs might share a commonm heatsink. In those cases the standoff height must be maintained as close as possible to the the original SMT setup in order to maintain. In those instances a mini stencil was the ticket. I also experimented at the time with solder paste dipping, which provided good results, though still not as much metal (and standoff height) as an SMT produced joint.

Regards

`Hege

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#65228

Reworking BGA's | 13 October, 2011

I guess I'll be different that the rest here. To stay consistent, I feel the best way is to use stencils to apply paste to the board first. We put paste on the board at SMT to solder them on initially. Then not when they get reworked? Why not take the few minutes to apply the paste and give yourself the best chance for success.

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#65229

Reworking BGA's | 13 October, 2011

Ease and consistency of applying solder paste to the board is depends on the layout. With adjacent components being as close as 0.5 or 1mm from the BGA, its difficult to say the least, to position a stencil and paste the board. Applying solder paste directly to the spheres of a BGA either via a stencil or dipping it in paste (much like flux) makes life a lot easier.

>>We put paste on the board at SMT to solder them on initially. Then not when they get reworked? When assembling the board, solder paste is applied to the BGA and all other SMT pads since the stencil was fabricated with those openings. If the openings for the BGA are excluded, it can still be installed properly but would have to be dipped into flux prior to placement.

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