Stencil Technical Specifications
Opening Process Standards
Stencil aperture processing follows industry standards:
- IC packages (QFP, SOP, etc.): Standard reduction applied for optimal paste volume
- BGA packages: Aperture ratio optimized for ball pitch
- 0805+ passives: Standard footprint apertures
- 0603 and smaller: Custom aperture sizing may be needed
If you need exact paste layer matching without reduction, add a remark: “Use exact paste layer openings, no aperture modification.”
Reducing Engineering Questions
To speed up your stencil order processing:
- Include complete paste layers (top and/or bottom as needed)
- Ensure paste layer matches your actual component footprints
- If paste and solder mask layers differ intentionally, note this in remarks
- Specify any custom thickness requirements upfront
- For multi-design stencils, ensure clear separation between designs
Solder Beading Prevention
Solder beading occurs when excess solder paste flows under component bodies during reflow. To prevent this:
- Reduce aperture size for large pads (QFN center pads, thermal pads)
- Use a grid pattern for large thermal pads instead of a single opening
- Consider using a thinner stencil (0.1mm) for fine-pitch components
- Add solder paste relief grooves in your pad design
Stencil Size Selection
Choose a stencil size that provides adequate clearance around your PCB:
- Non-frame stencils: at least 8mm clearance on each side for clamping
- Frame stencils: the valid printing area is inside the adhesive tape boundary
- For Top+Bottom single stencils: valid area must be at least 2× your PCB dimensions
Electropolishing
Electropolishing smooths the aperture walls, improving paste release for fine-pitch components. Recommended for:
- BGA pitch ≤ 0.5mm
- QFP pitch ≤ 0.4mm
- 0402 and smaller passives
