What are the causes and solutions for solder beads appearing during Solder Paste printing? During the reflow process, many skilled technicians encounter solder beads. This phenomenon results from the combined effect of many factors in production. The causes include the product itself, environmental issues during soldering, moisture in the solder material itself, and formulation problems. So, what causes solder beads during production? If you want to know how to solve this problem, as a Solder paste manufacturer, let me introduce it to you:

1. Solder paste warm-up time was insufficient, causing moisture absorption after printing. Improper PCB storage caused the board to become damp. When passing through the reflow oven, tin explosion occurred, resulting in solder beads.

Answer: Extend the solder paste warm-up time to 3-4 hours, strengthen PCB storage, and bake the PCB before use.

2. The solder paste printing stencil is not clean and contaminates the PCB. The stencil is too thick, resulting in excessive solder paste deposition. The stencil openings are improper, causing solder paste to overflow the pads during reflow and form solder beads after the oven.

Answer: Clean the stencil more frequently, adjust stencil thickness, use anti-solder-bead stencils, and modify stencil openings.

3. During solder paste printing, squeegee pressure and angle were set incorrectly, resulting in excessive solder paste on the pads. After reflow, the molten solder overflowed the pads, causing solder beads.

Answer: Adjust the angle and pressure of the squeegee.

4. Solder Paste Viscosity is high, printing performance is poor, and solder powder sphericity is poor, leading to uneven solder paste deposition on the pads. During reflow, the Flux on the pads evaporates quickly, resulting in insufficient flux cleaning activity and excessive surface tension, which causes solder beads.

Answer: Reduce solder paste viscosity, improve printing performance (thixotropic index), and use high-quality solder powder. If the metal content is too high, reduce the alloy ratio in the solder paste.

5. The placement machine's placement accuracy is insufficient, and placement pressure is too high, causing solder paste to overflow the pad after placement and form solder beads after reflow.

Answer: Adjust the placement accuracy and pressure of the placement machine.

6. Solder paste slump performance is poor. During reflow, the solder paste collapses under heat and overflows the pads, resulting in solder beads.

Answer: Adjust the slump performance of the solder paste.

(a) If solder paste activity is insufficient, enhance the activity of the solder paste formula. (b) If viscosity is low, adjust the solder paste viscosity, adjust the flux paste formula, and increase the metal content of the solder paste.

7. Furnace temperature curve: chain speed is too fast, and the chain shakes severely.

Answer: Adjust the furnace temperature curve, reduce chain speed, and repair chain vibration.

8. Solder paste activity is insufficient, the pads are severely oxidized, and the pads are not properly cleaned before reflow, resulting in uneven surface tension between the pads and the solder, which causes solder beads.

Answer: Enhance solder paste activity. When increasing activity, factors such as shelf life and printing life should be taken into account.

9. After printing, solder paste release was poor, causing the solder paste to tip. During SMT, the solder paste overflowed the pad, and after reflow, solder beads appeared.

Answer: Adjust the printing performance of the solder paste (adjust the thixotropic index of the solder paste).