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0402 pad and stencil aperture design

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0402 pad and stencil aperture design | 30 October, 2008


I have a new 0402 pad design on a recent board were building in future. On closer look i thought the pad was a thru hole mount , but upon closer inspection the round pads are for 0402 comps.

I had a discussion with the engineer and he said this design was for BGA purposes- bring the decoupling really tite (still trying to wrap my head around this explanation)

If anyone is using round pads for 0402 comps, what stencil apertures are being used . ie round 1-1?

Is there any mention in IPC 7351A for this type of pad design?

Is there anything i need to watch out for during my production process-tombstoning.....

Thanks for any help


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0402 pad and stencil aperture design | 30 October, 2008


Sounds like your engineer does not know what he's doing. We have developed and built hundreds of thousands of boards with normal square pads for 0402, and we just use a 5 thou stencil with 5% reduction and it works well.

Decoupling? What is that, and it sounds like he's completely unqualified, as pad shape won't effect that at all. Or your engineers trying to be a process engineer.

This is a problem that happens sometimes where design engineers, because they have higher qualifications, think they know everything about process development, and just do things without asking process people. You need to watch for this all the time, because generally they screw it up badly.


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0402 pad and stencil aperture design | 30 October, 2008

For most applications, a nice square [or rectangle] pad works just fine. Assemblers ship boat loads of boards with these every day.

It's reasonable for tight decoupling capacitor requirement applications to use round or radiused pads for components at BGA pads and via. For some applications, that you can imbed termination resistors and decoupling capacitors into a 1mm BGA via grid on the back side of a board is a very BIG DEAL! The round pads allow you to do this. Other shapes work also, but square or rectangle do not work.

As Grant says, some times designers get a little carzed when they thry to implement RF designs. So, why not check-out the design guidelines for the BGA used on the board to understand better if your designer is on-track or in need of an alignment?

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0402 pad and stencil aperture design | 31 October, 2008

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