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Date: | Fri, 5 Oct 2012 11:29:52 -0500 |
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Hi Phil - At the top of my possible root cause list would be the reflow
profile which is easy to investigate and change if necessary.
Dave Hillman
Rockwell Collins
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Phil Nutting <[log in to unmask]>
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[TN] solder splash under SMT caps
Here is my question for today.
We have an SMT board that measures 16 inches by 17 inches be 0.062 thick
(it is well supported in the end application) with 32 voltage multiplier
circuits so the board develops 12.5kV. On the 2225 capacitors we had
failures (arcing) under the parts and our customer removed some caps only
to find solder splashes. We used the standard IPC pad configuration for a
2225 part (3.7mm gap) with no solder mask under the capacitor, ENIG finish
and I suspect tin/lead paste. I have a photo I will post if Steve Gregory
is still offering his site.
Our customer wants us to use a specific capacitor by AVX and the AVX pad
layout of 4.6mm gap. Our contract manufacturer wants us to open up the gap
between pads by 1mm (essentially the 4.6mm recommended by AVX).
My theory on this failure is the following; (could be any one or a
combination of any items listed below)
Too much solder paste
Incorrect reflow pre-heat
Incorrect liquidus temp
I have read John Maxwell's white paper and see that he recommends a larger
space, but he didn't see significant performance enhancement above the
1808 part. Refer to
http://johansondielectrics.com/technical-notes/application-notes/new-impact-of-pad-design-and-spacing-on-ac-breakdown-performance.html
.
I agree that this greater distance will help with arcing, but will it help
with the solder splash?
Will separating the pads have that much affect that the solder will be
drawn out to the outside visible pads?
Inquiring minds want to know....
Phil Nutting
Design for Manufacturing Engineer
Kaiser Systems, Inc.
126 Sohier Road
Beverly, MA 01915
Phone: 978-922-9300 x1310
Fax: 978-922-8374
e-mail: [log in to unmask]<mailto:[log in to unmask]>
www.kaisersystems.com<http://www.kaisersystems.com>
www.linkedin.com/in/philnutting<http://www.linkedin.com/in/philnutting>
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