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Printed Circuit Board Assembly & PCB Design Forum

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BGA Soldering

#31163

BGA Soldering | 31 October, 2004

Can BGA's really be reliably attached without adding any extra paste? Just use the BGA balls and tacky flux? We are interested in the Pro's and Con's. Seems like a lot of different opinions out there.

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Steve

#31164

BGA Soldering | 31 October, 2004

I believe on High Temp. Spheres you require paste eutectic 63/37. The solder paste forms an intermettalic bond to the pad and a bond to the surface structure of the high temp sphere. The standard 63/37 alloy spheres will melt during reflow and form their own intermettalic bond with the pads. Ersa (manufacturers of the Ersascope) has a neat presentation of the "double drop" that SHOULD occur during the transformation of the sphere during reflow, eutectic that is. Hope this helps.

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Bob R.

#31174

BGA Soldering | 1 November, 2004

Yes, you can place a BGA in flux and get good reflow. However, depending on BGA type and size you should expect a yield loss due to coplanarity issues. Having the paste on the pad definately helps your yield.

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#31182

BGA Soldering | 1 November, 2004

There is no IPC requirement for reworking BGA with either paste or just flux. While we generally use flux only, general consensus is that both methods work equally well. Adding solder paste, while more difficult, should result in larger package stand-off which will improve reliability.

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#31183

BGA Soldering | 1 November, 2004

Good stuff! Thanks to all. mk

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Ken

#31188

BGA Soldering | 1 November, 2004

Agreed. You will find different part manufacturers have different coplanarity specs.

In fact I have on supplier that calls out 7 mil max coplanarity. Then factor in board bow and twist and it becomes a real joy.

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#31200

BGA Soldering | 2 November, 2004

Isn't that a good reason to use more paste? With just the paste from the balls, do you really get as good a solder joint as with a standard amount of solder paste added? What about voids? Do they go away by not using paste? I am talking about initial application, not rework.

mk

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RDR

#31202

BGA Soldering | 2 November, 2004

I have never experienced voids when using the flux only for application. Search the archives for void causes. As far as "more paste is better" I think that could be a true statement if we are talking about adapting to co-planarity type issues. My experience has shown that the ball collapse in many instances will exceed the differences in co-planarity. The gotcha in this is when both the board and the part start moving into or away from each other during reflow then I beleive that paste will improve the process. The solder joint integrety should not be any different between a ball attached with paste vs. flux only. the only difference I have found is the finished ball size. For whatever it is worth the actual amount of solder that you will get from paste is around 5% of the total volume of the ball after reflow.

thought I'd throw my 2 cents in. Russ

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