There are several reasons why voids can occur when soldering THT components.

One reason could be that the solder pin including the solder pin casings seal the hole where the pin is placed tightly from above and thus prevent the air from escaping upwards from the solder joint. In this case it is possible that the hole diameter is too narrow for the pin and that the pin has to be adjusted during a product review.

Another reason may be a steam cushion created by the flux. This cushion creates an increased vapor pressure which vents through the solder joint. This creates cavities and crater-shaped defects in the surrounding solder-meniscus.

Vapor pressure can also be generated in the circuit board if the moisture in the circuit board forms a vapor cushion during the soldering process and expands in the form of a void at the solder joint. For this reason, printed circuit boards should be dried for about 1 to 2 hours at 80 to 100°C after being manufactured.

A further 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, it has different effects 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 thoroughly cleaned.
• Hence, the cleanliness of the PCB and the components must be checked before the manufacturing process.
• The same applies to wettability.
• Furthermore, general cleanliness should be ensured, for example by wearing gloves when handling PCBs and components.

Often the devil is in the details when it comes to precision fluxing. If you can adjust the flux application that applies the flux to the board, you can control the result quite accurately, even if the flux is applied quite quickly. New smartphones, in combination with a flashlight, are able to record videos at 60fps (frames per second). When a flashlight is used to illuminate the flux stream, you can detect it quite easily and see where it is applied.

In order to keep the assembly clean, you can also hold a thermal paper or sandwich paper in between. This paper clearly shows the direction of the flux stream. A small glass panel can also be used.

The positions can then be optimized and the performance parameters of the dispenser should be adjusted. This is done via the software of the machines. The ratio of speed, time and power of the dispenser is important. The simplest way to control the flux is the automatic module for flux stream control, which under certain circumstances can also be retrofitted in an Eutect systems.