The PCB pad cannot be tinned, what is the reason?
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The PCB pad cannot be tinned, what is the reason?

Posted Date: 2024-01-18

The PCB pad cannot be tinned, what is the reason?

There may be many reasons why the PCB pad cannot be tinned. The possible reasons and solutions will be introduced in detail below.

1. Solder paste quality issues

First, you need to confirm whether the solder paste used is qualified. Poor solder paste quality may cause the pad to fail to be tinned. One possible situation is that the solder paste has expired. The validity period of solder paste is often 12 months. Expired solder paste may have problems with drying and changes in chemical composition. In addition, the tin content of the solder paste will also affect the quality of the tin on the pad. When the tin content in the solder paste is low, it may lead to poor tin on the pad.

Solution:

Purchase fresh solder paste and make sure it is within the expiry date. At the same time, confirm that the tin content of the solder paste meets the soldering process requirements.

2. Contamination of solder pad surface

Contamination on the pad surface will also prevent the pad from being tinned. During the manufacturing process, the pads may be contaminated by impurities such as dust, grease, oxides, etc. These contaminants may hinder the wetting and soldering solidification of the solder paste. In addition, if there are oxides on the surface of the pad, the tin affinity of the pad will be reduced, making it impossible to apply tin to the pad.

Solution:

Clean the pad surface and use a professional cleaner to remove contaminants such as grease and dust. If oxide is present on the pad surface, a deoxidizing agent can be used to remove the oxide layer.

3. Solder paste viscosity problem

The viscosity of the solder paste also affects the quality of the tin on the pad. If the viscosity of the solder paste is too high, it will be difficult to coat the solder pad surface; if the viscosity is too low, the solder paste may be too fluid and unable to remain on the pad surface.

Solution:

The viscosity of the solder paste can be adjusted by heating or adding an appropriate amount of diluent.

4. The welding temperature is inappropriate

Soldering temperature is one of the important factors affecting tin on the pad. If the soldering temperature is too low, the solder paste will not be able to fully melt and wet the pad surface; if the soldering temperature is too high, the pad and the components on the pad will be thermally damaged.

Solution:

Adjust the soldering temperature to ensure that the soldering temperature is within the melting point range of the solder paste and follow the soldering process specifications.

5. Unreasonable pad design

The design of the pad may also affect the quality of the tin on the pad. If the pad design is unreasonable, such as the pad is too large or too small, it will cause difficulty in tinning the pad.

Solution:

Reasonably design the pad size to ensure that the pad size and spacing meet the welding requirements. Pads can be optimized according to welding process specifications.

6. Welding process issues

Problems with the welding process may also cause the pad to fail to be tinned. For example, if the welding time is too long or too short, it will affect the wettability of the solder paste and the welding quality.

Solution:

According to the welding process specifications, adjust the welding time and welding speed to ensure that the welding quality meets the requirements.

In addition to the common reasons mentioned above, there are other factors that may cause the pad to fail to be tinned, such as quality issues with the soldering pen or tip, unskilled soldering techniques, etc.

When solving the problem that tin cannot be applied to the solder pad, it is necessary to carefully investigate the possible causes and take corresponding measures according to the actual situation. Through reasonable solder paste selection, pad cleaning, soldering temperature adjustment, welding process optimization and other methods, the problem of soldering pads not being able to get tin can be effectively solved and the welding quality improved.


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