Step Stencils - Available in All Stencil Technologies
 Step stencils have been available as a stencil option for many years. They are normally required to provide additional paste height in certain areas of the PCB (Step-Up Stencils), or to provide lower solder paste height in certain areas of the PCB (Step-Down Stencils). There are also applications where the PCB has raised areas on the surface of the board. In this case, a Step Relief Pocket is required on the PCB side of the stencil. Photo Stencil offers Step Stencil options for all technology stencils: AMTX E-Fab®, Hybrid, Laser and Chem-Etch.
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Advantages
Step Stencils offer the SMT process engineer significant flexibility in achieving the proper solder paste height and solder paste volume for the overall paste printing process.
Note: Steps are available on the PCB side, the squeegee side, or on both sides of the stencil.
Step-Down Stencils
- 20 mil pitch QFP: 7 mil thick for R’s and C’s with a step-down to 5 mil for 20 mil pitch QFPs
- 16 mil pitch QFP, 0201s and/or µBGA’s: 5 mil thick stencil with a step down to 4 mil for the 16 mil pitch QFP, 0201s, and or µBGAs.
Step-Up Stencils
- CBGA or CGBGA: 6 mil for normal components and a step-up to 8 mil for CBGAs. Extra paste height required for this component due to possible coplanarity issues.
- Through-Hole Connector: 6 mil for normal components and step-up to 10 mil for the through-hole connector.
Relief Step-Board Side
Bar Code Relief: When the bar code is too close to PCB pads it can cause a gap between the stencil apertures and the pads. The relief pocket allows the stencil to cleanly gasket to the PCB.
Raised Via Pads: Raised via pads can prevent the stencil from gasketing to the PCB surface. A relief-step pocket around the vias prevents this situation.
Relief for Paste (Two Print Stencil): The Two Print Stencil is used to print solder paste on a board which already has solder bricks on the PCB surface from a previous print cycle. An example would be a 12 mil thick glue stencil with an 8 mil deep relief-step pocket around SMT solder paste bricks.
3-D AMTX E-FAB® Stencils
 Electroform stencils can be manufactured with deep relief-step pockets on the PCB side of the stencils. This stencil thickness is uniform (6 mils for example) even though the step-relief pocket can be as deep as 30 mils. Thus, the term 3D AMTX E-FAB is used to describe this stencil technology.
- PCB BGA Package with Chip Devices in the Center of the Package: 3D AMTX E-FAB step stencil with a relief-step pocket 30 mils deep to give clearance for the Chip Devices while the stencil is 6 mils thick for printing solder paste for flux on the BGA pad sites.
- PCB has a Raised Heat Sink in the Board's Surface: The 3D AMTX E-FAB stencil has a 20 mil deep relief-step pocket to provide clearance around the heat sink.
Step Design Guidelines
| Type of Step |
Keepout Distance
(Aperture to step edge for
an aperture in the step) |
| Squeegee Step-Up |
35 mils / mil of step |
| Squeegee Step-Down |
35 mils / mil of step |
| Contact Side Step-Up |
25 mils |
| Contact Side Step-Down |
25 mils |
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