Hi Siegfried!

From experience at a past job, concave terminations are best for reflow 
soldering. I worked for a company named SMART Modular Technologies where we built 
memory modules. The one I remember well that used chip resistor networks was a 
Pipeline Burst Cache Module that had 21 chip resistor networks on the 
backside...this was a double-sided reflow assembly. When we first started building it, 
we had many bridges and mis-alignments. The footprint was what was 
recommended by the manufacturer of the resistor network that we were using at the time, 
and it was a convex terminated network. I think I must have bought 2-3 
different stencils all with different aperture openings to try and improve yields. 
Things got a little better, but the problems never really went away.

Then we had this Panasonic Rep in, and I started talking with him about the 
problems we were having. He immediately pulls this paper out of a study that 
was done by Panasonic on concave vs. convex chip resistor networks reflow 
soldering performance, and it showed that concave network terminations had better 
self-centering characteristics, and less bridging. I tried to find that paper up 
on the web, but no joy. Here is a link to a page in Digikeys catalog to a 
Panasonic resistor network that says that concave terminations solder better:

http://dkc3.digikey.com/pdf/EU041/0601.pdf

In my case at SMART Modular, switching to networks with concave terminations 
almost completely eliminated the solder defects we were experiencing with chip 
resistor networks.

I've requested the paper I remember from Panasonic, it's pretty good with 
some nice images. If they still have it, and I get it, I'll share with everybody.

-Steve Gregory-


> Dear TechNetters,
> 
> we are using more and more chip resistor arrays. They are available in 
> concave and two convex (scalloped edge, square edge) types. The concave one is 
> some expensive and less disposable, but I heard that it is easier to solder 
> giving better quality. 
> 
> Any opinions and informations comparing the different types (concave, 
> convex) are welcome.
> 
> Thank you in advance for your help.
> 
> Siegfried Meier
> Dipl.-Ing.
> 
> Entwicklung selbstfahrende Erntemaschinen
> Müller-Elektronik GmbH u. Co.
> Franz-Kleine-Str. 18
> D-33154 Salzkotten
> 
> Tel: +49 5258 9834-70
> Fax: +49 5258 9834-94
> email:  [log in to unmask]
> Internet: http://www.mueller-elektronik.de


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