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Lead Free Stencil Design

Lead Free Stencil Design

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Most Lead Free Solder suppliers are saying that stencil aper... - Jul 12, 2005 by

Hi, My stencil maker also say the same thing on 1:1 for l... - Jul 12, 2005 by

The reason for going 1:1 with lead free is that it does not ... - Jul 13, 2005 by RDR

Thanks a lot folks! Seems like 1:1 in generally accepted. Ho... - Jul 13, 2005 by

Are you seeing solder balling on your discretes when you pri... - Jul 13, 2005 by

We do have solder balling on occasion but it is usually very... - Jul 13, 2005 by RDR

I know this is asking a lot, but could you please tell us wh... - Jul 13, 2005 by

I read the Cookson/Alpha paper "Optimizing stencil design fo... - Jul 13, 2005 by jdengler

The problems we saw had to due with the Flux I believe. We ... - Jul 13, 2005 by RDR

This works for me with ENIG finish and a SAC305 NC paste Re... - Jul 13, 2005 by

Thanks Again Everyone! One more question... Do you suggest... - Jul 14, 2005 by

Stencil thickness is related to PCB design and is not relate... - Jul 14, 2005 by RDR

Tom

Lead Free Stencil Design | 12 July, 2005

Most Lead Free Solder suppliers are saying that stencil aperatures should go to 1:1 or have no change from previous stencils design. Only one solder supplier seems to be complicating the process....is their solder very different?? Can anyone share stencil design experiences/tests? Do people generally agree that stencil aperatures should be 1:1 in lead free?

Chris Ong

Lead Free Stencil Design | 12 July, 2005

Hi,

My stencil maker also say the same thing on 1:1 for lead free. I am using electro-form stencil. You can look for Mr Richard or Mr Chong at wkchong@dek.com.

Hope this info will be useful for you

Lead Free Stencil Design | 13 July, 2005

The reason for going 1:1 with lead free is that it does not spread out like the pb solders. So 1:1 is really not necessary in my opinion. We go 1:1 anyway on discrete components along with other packages. You always have to make sure that the area and/or aspect ratio is acceptable for stencil design.

Tom

Lead Free Stencil Design | 13 July, 2005

Thanks a lot folks! Seems like 1:1 in generally accepted. However Cookson/Alpha seem to be the only ones complicating homeplates to "roundy" instead of "triangular". I'll do some tests... Thanks again!

Bob R.

Lead Free Stencil Design | 13 July, 2005

Are you seeing solder balling on your discretes when you print 1:1? Are you washing your boards?

Lead Free Stencil Design | 13 July, 2005

We do have solder balling on occasion but it is usually very minimal. When and if this becomes an issue with us we will then utilize the homeplate aperture. We do not wash boards as a general rule. All of our pb free has been no-clean. We can't find a good water soluble lead free yet.

Bman

Lead Free Stencil Design | 13 July, 2005

I know this is asking a lot, but could you please tell us what WS LF pastes you have looked at? What issues are you seeing with these WS pastes?

Thanks

Lead Free Stencil Design | 13 July, 2005

I read the Cookson/Alpha paper "Optimizing stencil design for Lead-free SMT processing". I interpreted it to mean that if you had a mid chip solder ball (MCSB) problem the "radiused inverted home plate of 20/60/20 style" had the greatest impact on reducing MCSB's while not increaseing tombstoning.

Jerry

Lead Free Stencil Design | 13 July, 2005

The problems we saw had to due with the Flux I believe. We saw what I would call poor coelescence and the residues were very hard for us to clean with our Water only cleaner. I will not lie and say I worked on the process very much. Since we already had/have a great no-clean process with the lead free I did not spend much time on it to see if the results could be improved. I would rather you E-Mail (click on my name) me off line for the manufacturers I tried.

Russ

Darby

Lead Free Stencil Design | 13 July, 2005

This works for me with ENIG finish and a SAC305 NC paste Reduce all pads by -2mil on all sides ie 0.050" x 0.050" becomes 0.046" x 0.046" EXCEPT Anything smaller than 30mil; -1.5mil Anything smaller than 20mil; -1mil Anything smaller than 15mil; -0.5mil Anthing smaller than 11mil; no reduction. BGA - don't know. 0201 - don't know. Stencil thickness is 0.005" (5mil).

Tom

Lead Free Stencil Design | 14 July, 2005

Thanks Again Everyone! One more question... Do you suggest to use 5 mil stencils? My existing stencils are all 6 mil and 8 mil. Should I change them?

Lead Free Stencil Design | 14 July, 2005

Stencil thickness is related to PCB design and is not related to paste type. If you release with a 8 mil stencil then use an 8 mil stencil. Of course there are pastes that release bteer than other and what not but use area and aspect ratios to determine stencil thickness.

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