Common Causes of Poor PCBA Labor and Materials

• Stand Up Issues

  • Uneven tension due to variations in copper and solder pad sizes
  • Excessive preheating rate
  • Misalignment in machine placement
  • Uneven solder paste printing thickness
  • Uneven temperature distribution in the reflow furnace
  • Deviations in solder paste printing
  • Loose machine track splints leading to mounting deviations
  • Machine head vibrations
  • Excessive solder paste activity
  • Incorrect furnace temperature settings

• Short Circuits

  • Excessive distance between stencil and PCB causing short circuits
  • Component mounting height set too low, leading to short circuits
  • Poorly made stencils (excessive thickness, long pin openings)
  • Solder paste unable to support component weight
  • Deformation of stencil or squeegee causing thick solder paste printing

• Offset

  Issues with positioning reference points, loose clamping, misaligned thimbles, and malfunctioning optical positioning systems.

• Missing Parts

  Various factors like inadequate carbon sheet, blocked suction nozzles, improper detection, incorrect mounting height, damaged trachea, and foreign objects causing missing parts.

• Empty Welding

  Factors such as weak solder paste activity, poorly defined stencil openings, excessive scraper pressure, inadequate component lead flatness, dirty PCB surfaces, and placement offset issues leading to empty welding.

Reasons for Insufficient Solder Joint Luster in SMT Processing

• Challenges in achieving consistent brightness of solder joints in SMD processing due to various factors:

  1. Oxidized tin powder in solder paste
  2. Additives in flux causing matte finish
  3. Low preheating temperature retaining residual evaporation
  4. Residual rosin or resin affecting solder joint brightness
  5. Discrepancies between solder-free and soldered products after using silver solder paste