In addition to the printing issues, could it also be that the reflow profile can play some role in this issue?
The pad where the solder splash originates has a smaller copper pour than the other and would reflow first causing that end to be pulled down to the board before the other side, squeezing solder underneath the cap towards the middle.
BR,
David Bealer
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of stephen gregory
Sent: Friday, October 05, 2012 7:18 PM
To: [log in to unmask]
Subject: Re: [TN] solder splash under SMT caps
Hi Phil,
Got your photo. Sorry about the delay in getting it posted but I had to rush off to work after I first replied to you, and now I'm getting a break to get it
posted:
http://stevezeva.homestead.com/1501136_solder_splash.jpg
It sure looks like too much paste to me. Do you know what stencil thickness was used? and what aperture size for the pads were?
You said that there was no soldermask in between the pads, but it sure looks like there's mask there to me...
Steve
________________________________
From: Phil Nutting <[log in to unmask]>
To: Steve Gregory <[log in to unmask]>
Sent: Fri, October 5, 2012 12:22:41 PM
Subject: RE: [TN] solder splash under SMT caps
Steve,
Thanks!
Phil
-----Original Message-----
From: Steve Gregory [mailto:[log in to unmask]]
Sent: Friday, October 05, 2012 12:19 PM
To: Phil Nutting; [log in to unmask]
Subject: Re: [TN] solder splash under SMT caps
Phil,
Send the photo my way, I get it posted...
Steve
-----Original Message-----
From: Phil Nutting
Sent: Friday, October 05, 2012 9:55 AM
To: [log in to unmask]
Subject: [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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