Hi Kane
Photo Stencil manufactures both Laser-Cut and Electroform step stencils. The normal step keep-out design guides are found in IPC 7525. 35 mils per mil of step thickness is recommended as keep out for apertures in the 3 mil area to the step-up to 5 mils. 25 mils keep-out from the step-down to 3 mils to an aperture in the 5 mil thick area.
Regards,
William E. Coleman Ph.D.
Vice President Technology
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]]On Behalf Of Kane, Amol (349)
Sent: Wednesday, August 27, 2008 8:27 AM
To: [log in to unmask]
Subject: [TN] FW: Step Stencil Requirements
_____________________________________________
From: Kane, Amol (349)
Sent: Wednesday, August 27, 2008 8:13 AM
To: [log in to unmask]
Subject: Step Stencil Requirements
Dear Technetters,
I am looking for some information about using step stencils in production. I have a 16 mil pitch QFN component with 7.8 mil square pads. This gives me unacceptable area ratio using a 5 mil stencil. Looks like I am going to have to use a 3 mil thick stencil with this component. I was thinking of using a 5 mil stencil with a 3 mil step. There are chip components around the QFN device. The board is Lead-Free with ENIG finish. Using a Type 4 solderpaste.
I was looking for inputs from folks who are using step stencils on the squeegee types (metal vs. poly), changes in print parameters (speed, pressure, Snap off etc,), board design considerations (keep out areas around the component needing the step), resources I could go thru to obtain more information, stencil houses who specialize in this process, and common pitfalls.
Any inputs will be greatly appreciated.
Thanks,
Amol
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