Stencil Design and Its Impact on SMT Yield
The stencil is the first link in SMT quality. Get the aperture geometry wrong and you inherit tombstoning, bridges and insufficient solder that no AOI can fully rescue.
Area and aspect ratio
Keep area ratio above 0.66 and aspect ratio above 1.5 for reliable release. Below that, paste sticks in the aperture.
Step-down stencils
Mixed component sizes benefit from local thickness reduction so small parts are not drowned in paste.
Nano-coating
A nano-coating reduces paste adhesion to the foil, improving release and extending stencil life.
Key Takeaways
Key Takeaways
- Target area ratio >0.66 and aspect ratio >1.5.
- Use step-down for boards mixing large and tiny parts.
- Nano-coating improves release and stencil life.
