Along with too much paste, there may have been a slight shift of the PCB to
the right when it was being pasted.

Toby
On Oct 5, 2012 8:23 PM, "Wenger, George M." <[log in to unmask]>
wrote:

> Steve,
>
> From the photo it appears you are correct.  Squeeze out solder paste.  Too
> much solder.  Phil should reduce his aperture and/or decrease stencil
> thickness
>
> Regards,
> George
> George M. Wenger
> Senior Principal Reliability / FMA Engineer
> Andrew Corporation - Wireless Network Solutions
> 40 Technology Drive, Warren, NJ 07059
> (908) 546-4531 Office (732) 309-8964 Mobile
> E-mail: [log in to unmask]
>
> -----Original Message-----
> From: TechNet [mailto:[log in to unmask]] On Behalf Of stephen gregory
> Sent: Friday, October 05, 2012 8:18 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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