Hi Tom!

There's a few articles out there that talk about "Phased Reflow Soldering".
Here's a link to one:

http://www.reed-electronics.com/semiconductor/index.asp?layout=article&
articleid=CA274087&industryid=3026

Something I've done in the past that works really well in my opinion, is to
use a 2%
silver solder paste. Sn62/Pb36/Ag2...works in the same way that Phased Reflow
does.
The difference is pretty dramatic when it comes to eliminating tombstones!

-Steve Gregory-


> Greetings All,
>
> I am having my first experience working with an assembly design that
> involves 0402 capacitors with underside solderable terminations (vice
> wrap-around end terminations)... The reflow process seems to cause the
> components to tilt and skew to highly unacceptable levels. Physically it
> looks as if the caps floated to the top of the molten solder volume (as if
> on pontoons) then slid down one way or the other. The vendor made a few
> recommendations including migration to a thinner (4 mil) stencil as well as
> some pad design and nitrogen tweaks and... Even after implementing these
> recommendations we are experiencing the same problems, just to a slightly
> lesser (although still unacceptable) degree... Does anyone out there have
> any additional thoughts on how to remedy this sort of issue?
>
> We do build another part [successfully] with a similar style component, but
> it is a 1206 form factor and is perhaps massive enough to keep from floating
> up the way the 0402 caps do...
>
> Your collective wisdom is greatly appreciated!
>
> Best Regards,
>
> Tom Ochenas
> Process Engineering
> Maxtek Components Corporation
> 2905 SW Hocken Avenue
> Beaverton, OR 97005
> [log in to unmask]
> desk: 503-627-3078
> fax:  503-627-4651
>


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