Here are some tips for stencil design:
- Choosing the Right Stencil Thickness
Stencil thickness directly affects solder paste volume.
Too thick? Risk of bridging. Too thin? You get cold joints.
Recommended thickness:
- 10 mm (4 mil)--Ideal for small components like 0402, QFNs, or CSPs
- 12–0.15 mm--Works for most common SMD parts
- >0.18 mm--Used for large pads or through-hole paste-in-hole printing
For mixed-size components on the same board, consider step-down stencils to balance paste volume.
- Optimizing Aperture Size
Apertures should usually be slightly smaller than the pad to control paste flow.
Examples:
- QFPs:90% aperture area; length can be slightly extended, width reduced to prevent bridging
- 0402/0201:1:1 ratio works fine to prevent tombstoning
Key ratios to watch:
- Area Ratio ≥ 66--Ensures smooth paste release
- Aspect Ratio ≥ 5--Prevents paste from clogging in deep/narrow apertures
- Quick Takeaways
- Cold joints? Check if your stencil is too thin or under-apertured
- Bridging issues? Likely caused by too much paste or improper aperture sizing
- Mixed packages? Step stencils offer precise paste control across the board
In Hitech Circuits, We provide free DFM reviews for every order, optimizing stencil design before production to minimize costly rework. You can send your Gerber files over, let’s optimise your build.
