Common defects and causes of SMT reflow soldering

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In SMT chip processing, reflow soldering is a crucial process. It involves soldering the chip components to the circuit board pads through high temperature and then cooling them together, ensuring stability in the circuit board's use. However, certain process defects are prone to occur during reflow soldering, and it's important to analyze and resolve the reasons for these defects to ensure product quality. Below, I will organize and introduce the common defects and their causes in SMT reflow soldering.

1. Tin beads

Causes:

1. Misalignment of silk screen hole and pad, leading to inaccurate printing, which soils the PCB with solder paste.

2. Excessive exposure of solder paste to an oxidizing environment and high moisture absorption from the air.

3. Inaccurate and uneven heating.

4. Excessively fast heating rate and prolonged preheating interval.

5. Rapid drying of the solder paste.

6. Inadequate flux activity.

7. Presence of numerous small particle tin powders.

8. Inappropriate flux volatility during the reflow process.

The process approval standard for tin beads is: When the distance between pads or printed wires is 0.13mm, the diameter of tin beads must not exceed 0.13mm, or there can be no more than five tin beads within a 600mm square range.

2. Opens

Causes:

1. Insufficient solder paste volume.

2. Inadequate coplanarity of the component pins.

3. Inadequate wetting of tin, causing poor fluidity and thinning of the tin paste, leading to tin loss.

4. Pin sucking or nearby connection holes. Coplanarity of the pins is crucial, especially for fine-pitch and ultra-fine-pitch pin components. Applying in on the pads in advance can prevent pin sucking by slowing down the heating speed and heating the bottom surface more while reducing heating on the top surface.

Common defects and causes of SMT reflow soldering

3. Solder cracks

Causes:

1. Excessively high peak temperature causing sudden cooling of solder joints and resulting in solder cracks due to excessive thermal stress caused by rapid cooling.

2. Poor quality of the solder itself.

4. Hollows

Causes:

1. Material-related factors such as damp solder paste, high oxygen content in metal powder, use of recycled solder paste, oxidized or contaminated component pins or printed circuit board pads, and damp printed circuit board.

2. Process-related influences such as low preheating temperature and short preheating time, which results in solvent trapping and bubble generation during reflow.

5. Solder Bridges

The cause of solder bridges is generally thin solder paste, including low metal or solid content, low thixotropy, easy squeezing, large solder paste particles, and low flux surface tension. Excessive solder paste on the pad and high peak reflow temperature can also lead to solder bridges.

SMT reflow soldering is a complex process susceptible to various influencing factors, resulting in various defects that are generally hard to eliminate. Understanding the common defects and causes of SMT reflow soldering and paying careful attention to the operating process can help avoid defects. In case of any problems, timely analysis and resolution are key.

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– Experienced and skilled team

– State-of-the-art equipment

– Strict quality control

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– Competitive price