Non-wetting and De-wetting during Soldering

Non-wetting and de-wetting phenomenon is a common defect in the welding process, they are respectively manifested as incomplete contact between solder and base metal and retreat after partial wetting.

 

Non-wetting

Non-wetting refers to the formation of a discontinuous film of solder on the surface of the base metal after welding. In the case of non-wetting, the solder is not in full contact with the base metal, so that the uncovered base metal surface can be clearly observed.

This phenomenon can be caused by the following reasons:

1. the base metal does not have good solderability characteristics.

2. the flux used may be inactive or the flux may have deteriorated.

3. the presence of oil or grease on the surface prevents the flux and solder from making effective contact with the base metal.

 

 

 

De-wetting

Backwetting occurs when the solder first wets the surface of the base metal, but due to poor wetting, the solder shrinks, forming a thin film and forming separate balls of solder on the surface of the base metal.

The causes of this phenomenon include:

1. some form of contamination of the base metal surface resulting in partial wetting of the solder.

2. a certain level of metal impurities in the solder bath causing back-wetting of the solder.

3. welding temperature is too high or too long, the interface formed by the alloy layer is too thick, due to the alloy layer of poor wettability, resulting in the original has been wetted on the surface of the brazing material retraction, leaving only a thin layer had been wetting traces and the formation of de-wetting

 

Avoidance measures

1. improve the solderability of the base metal, through the material selection or surface treatment to enhance the affinity between the metal and the solder.

2. Choose active fluxes to ensure that they can effectively assist the solder in wetting the base metal.

3. Reasonably adjust the soldering temperature and time to ensure that the solder can fully wet the metal surface under appropriate conditions.

4. always thoroughly remove oil, grease and organic contaminants from the surface of the base metal before soldering to ensure good contact.

 

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