Common Problems in Solder Paste Printing and Solutions

Solder paste printing is responsible for over 70% of SMT defects. Here are common problems in solder paste printing and how to fix them, with support from SMTFullLine.

Problem 1: Bridging (Short Circuit Between Pads)

• Causes : Too much paste, stencil misalignment, excessive squeegee pressure.

• Solutions :

  • Reduce stencil thickness or aperture size.

  • Improve alignment (use vision system).

  • Decrease squeegee pressure by 10‑20%.

Problem 2: Insufficient Solder Paste (Volume Low)

• Causes : Clogged stencil aperture, low squeegee pressure, worn squeegee blade.

• Solutions :

  • Clean stencil frequently (under‑stencil wipe).

  • Increase squeegee pressure slightly.

  • Replace worn metal or rubber blade.

Problem 3: Smearing / Solder Paste Spread Outside Pads

• Causes : Stencil separation too fast, board not flat, too much paste.

• Solutions :

  • Reduce snap‑off speed.

  • Use vacuum table to flatten board.

  • Optimize paste viscosity (stir paste before use).

Problem 4: Uneven Paste Deposition

• Causes : Uneven squeegee pressure across stroke, worn blade edge.

• Solutions :

  • Level tooling pins and board support.

  • Replace squeegee blade.

Problem 5: Poor Paste Release from Stencil

• Causes : Stencil aperture walls rough, paste too sticky, insufficient separation speed.

• Solutions :

  • Use laser‑cut stencil with electropolish.

  • Try a different paste batch (newer).

How SMTFullLine Helps

We provide stencil printer calibration services, squeegee blades, under‑stencil cleaner rolls, and process training. Our semi‑auto and auto printers include recipe storage to reduce variability.

Print perfectly every time.
Contact SMTFullLine.com for a printing process audit.