There are various reasons why blowholes occur when soldering THT components.
One reason may be that the solder pin, including the solder pin housing environment, seals the hole in which it is inserted tightly from above and thus prevents the air from escaping upwards from the solder joint. In this case, it may be that the hole diameter for the pin is too narrow and needs to be adjusted during a design review.
Another reason may be a vapour cushion created by the flux. This cushion creates an increased vapour pressure, which is vented via the solder joint. This creates cavities and crater-shaped defects in the surrounding solder meniscus.
However, vapour pressure can also develop in the printed circuit board if the moisture in the printed circuit board forms a vapour cushion during the soldering process and expands explosively over the solder joint in the form of a crater. Printed circuit boards should therefore be left to dry at 80 to 100°C for around 1 to 2 hours after manufacture.
Another cause of thread voids is the different thermal masses of the components involved in the area of the solder solidification zones during cooling. Depending on the size of the defect, the volume of the solder joint and the location where it occurs, this results in different influences on the service life.
In principle, however, it can be said that a few measures should always be kept in mind:
- The components and the PCB environment should be cleaned.
- The cleanliness of the PCB and the components must therefore be checked before the production process.
- The same applies to wettability.
- Furthermore, attention should be paid to general cleanliness, for example by wearing gloves when handling circuit boards and components.
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