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RoHS BGA stencil question

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#47383

RoHS BGA stencil question | 8 February, 2007

Good Morning Everyone,

We have an application coming up with several BGA's on a RoHS assembly. One is a 25 mil ball on a 40 mil pitch, another is a 15 mil ball on a 40 mil pitch. In the past for leaded assemblies, we have used square apertures for 15 mil balls. This would cause a slight overprint onto the PCB (2 mils). Does anyone have any experience doing this with SAC305? I am concerned that this may leave orphaned solder paste on the PCB. Also, would you use a 4 or 5 mil stencil?

Any comments would be greatly appreciated.

Thanks In Advance

Chris

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#47405

RoHS BGA stencil question | 8 February, 2007

Good evening,

I do. 2mil overprint is not critical. Paste will simply flow back. Paste flows back even with larger overprint (up to 15mil at least). 5mil stencil thickness if fine also. BGA area ratio for both BGAs is higher than 0.66 required by IPC-7525. Paste will release.

BR, Pavel

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#47408

RoHS BGA stencil question | 8 February, 2007

We use 1 to 1 aperture on a 6 mil stencil, no problems. Do not over print unless your board resist allows you too.

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#47427

RoHS BGA stencil question | 9 February, 2007

Thank you so much for your input.

Greatly Appreciated.

Thanks

Chris

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