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Are you using Stepped Stencils?

Mark Laing

Mark Laing

Posted Oct 31, 2012
1 Comment

Hi there

We released our Valor MSS Stencil Design module a few months ago and have received positive feedback which resulted in a number of major enhancements that will be part of our up-coming release. However, a topic that I have discussed with a number of our users involves the use of a stepped stencil. Standard stencils have a single thickness across them meaning that paste volume can only be controlled by varying the aperture size. With a stepped stencil the thickness of the stencil can be changed to add another mechanism to control paste volume.

I am interested to hear from those of you who work with stepped stencils how you decide on whether to use a stepped stencil or not and how complex the step can become. When we vary the stencil aperture now we don’t have to consider the position of the component relative to the others around it. With a stepped stencil, the same component may be in the middle of other components that affect the stencil thickness and hence it cannot be considered in a stand-alone environment so a local change of the stencil aperture is needed to compensate for the paste volume.

Here is a link to our stencil capability we have today in Valor MSS:

http://www.mentor.com/pcb-manufacturing-assembly/products/valor-mss-process-preparation

Thanks

Mark

stencil, programming, vPlan, data preparation

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In determining the stencil max thickness for miniature component for a step-stencil, the stencil designer must calculate the aspect ratio (equal or greater than 1.5) and the area ratio (equal or greater than .66, but .50 works for electrofrom stencils). Also, per IPC-7525, stepped stencil components need the added requirement of "keep-out" zones away from other components not being "step". How can the stencil thickness issue be incorporated in to the Valor checks. More technical explanation of this issue can be review at photostencil.com in their tech forum. The current DFM/A checks do not address this issue of component mix of conventional SMT (Non-stepped) and miniature components (step) in regards to spacing between them and flagging a "step-stencil" condition or area.

Hector Garcia
6:31 PM May 21, 2013

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