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0402 aperture design lf

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aj

#48993

0402 aperture design lf | 12 April, 2007

Hi all,

What stencil aperture designs do you use for 0402 components?

Thanks in advance for replies.

aj...

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#48994

0402 aperture design lf | 12 April, 2007

There have been many designs of apertures for 0402, round, home plate, inverted home plate and various reduction amounts for square or rectangular apertures. What works best for a given application depends on PCB design, solder land finish, stencil thickness, stencil type (chem-etch, laser or electroform) and solder paste used.

The IPC-7525 Stencil Design Guidelines has just been updated this past Feb.

It is a great document for only $40.00

Go to http://www.ipc.org and type "IPC-7525" in the Product Search box in the upper left corner of the page.

Also, there is a Stencil Design document from Speedline Technologies- MPM called Stencil-Pro. Joe Belmonte can get it to you, jbelmonte@speedlinetech.com

http://www.speedlinetech.com/mpm/index.aspx

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#48995

0402 aperture design lf | 12 April, 2007

Hi aj,

Pete is right, there are several variables that can affect your quality when it comes to stencil design. A good idea is to have a stencil made with various designs incorporated into it. A lot of engineers like the reverse homeplate design. It provides a good area of paste to mount to without tomb-stoning, and doesn't solder ball after reflow. Depending on your application, I would think a 5 mil stencil would work well. If anything it's a starting point.

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aj

#49044

0402 aperture design lf | 14 April, 2007

the footprint is IPC standard which I have found to be less forgiving than the Jedec one for tombstoning.

Enig finish - 5 thou stencil.

We have historically used homeplate design but I am leaning towards 1:1.

Leadfree application.

aj...

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#49058

0402 aperture design lf | 16 April, 2007

Tombstone head and a graveyard mind. I would not recommend 1:1 due to solderpaste beed out opportunities. Have you tried the inverted home-plate?

Here are some good links on tombstoning and how to eliminate it:

http://www.aimsolder.com/technical_articles.cfm#14

http://www.indium.com/documents/techpapers/Lead-free_Controlling_Tombstoning_Behavior.pdf

http://blog.screamingcircuits.com/2007/02/index.html

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#49059

0402 aperture design lf | 16 April, 2007

"Although some lead-free pastes performed adequately and newer pastes work better than earlier formulations, this detailed experiment confirmed that tin/lead solder pastes wet back to PCB pads better than lead-free solder pastes. Therefore, a more accurate solder paste printing process is required in the use of lead-free solder pastes to compensate for this (Figure 3)." Look here: http://smt.pennnet.com/articles/article_display.cfm?Section=ARCHI&C=Feat&ARTICLE_ID=241624&KEYWORDS=lead-free%20solder&p=35

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#49090

0402 aperture design lf | 17 April, 2007

Our experience with leaded paste and SAC305, for 0402's, has been positive with the following stencil designs:

1.- 5 mil thickness. 2.- Home plate design.

Hope it helps.

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aj

#49109

0402 aperture design lf | 18 April, 2007

Hi,

Can you advise the footprint dimensions used on the PCB ?

Thanks,

aj...

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#49220

0402 aperture design lf | 21 April, 2007

Yes we can (at least show something that work for us) but hey, not possible to attach some pictures here... We don't have any problem with 0402:s on OK Corral... / Ps. Just get up mischief. Ds.

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#49250

0402 aperture design lf | 24 April, 2007

If the PCB you are using is a HASL pad finish and is a leaded assembly, we use homeplate pads with a 5 mil stencil.

If the circuit has Enig finish and is PB-Free then we use 1:1 apertures with a 5 mil stencil

Either method should provide no solderballs and good fillets for 0402 passives.

Good Luck.....

Chris

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aj

#49288

0402 aperture design lf | 25 April, 2007

Hi All,

Thanks for all the replies.

I went with 1:1 (ENIG Finish) and the results were very good.

aj...

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