Common Printing Shortcomings And Solutions of SMT Chip Processing

Solder paste printing is a very complex technology in SMT chip processing. It is not only affected by materials, but also directly related to equipment and parameters. After controlling every subtle link in the printing process, it can be said that details determine victory or defeat. In order to avoid the shortcomings that often appear in printing, the following are the most common shortcomings during solder paste printing and the corresponding avoidance or solutions.

1. The solder paste is too thin, the reason is:

• The template is too thin.
• The pressure of the scraper is too high.
• The solder paste has poor fluidity.

Avoidance or Solution: Select the template with the appropriate thickness. Select the solder paste with the appropriate particle size and viscosity. Reduce the squeegee pressure.

2. The Tip

The tip is the solder paste on the pad after printing, which may be caused by the gap of the squeegee or the viscosity of the solder paste.

Avoidance or solution: In SMT chip processing, the squeegee gap should be appropriately adjusted or a solder paste of suitable viscosity should be selected.

3. After printing, the thickness of the solder paste on the pad is not the same. The reason is:

• The template is not parallel to the printed circuit board.
• The solder paste is not mixed uniformly, making the particle size different.

Avoidance or solution: Adjust the relative orientation of the stencil and the printed board. Fully mix the solder paste before printing.

4. After printing, the solder paste falls to both ends of the pad. The reason is:

• The pressure of the scraper is too high.
• The positioning of the printed board is not firm.
• Solder paste viscosity or metal content is too low.

Avoidance or solution: adjust the pressure; re-fix the printed board; select the solder paste with the appropriate viscosity.

5. The thickness is not the same. There are burrs on the edge and surface, which may be caused by the low viscosity of the solder paste and the roughness of the stencil opening hole wall.

Avoidance or solution: Choose a solder paste with a slightly higher viscosity. Check the etching quality of the stencil opening before printing.

6. Incomplete printing. The solder paste is not printed in some places on the pads. The cause may be:

• The opening is blocked or some solder paste sticks to the bottom of the template.
• The viscosity of the solder paste is too small.
• There are large-scale metal powder particles in the solder paste.
• The scraper is worn.