Causes and Solutions of PCBA Pseudo Soldering

PCBA pseudo soldering is a problem that affects the quality of the finished PCBA. It can cause losses due to rework, which reduces the production efficiency. However, detecting and solving pseudo soldering problems can be done using inspection.

Reflow soldering

Reflow soldering is one of the most common methods of PCB assembly. This method is often combined with wave soldering. It can greatly affect the quality of the assembled board, which is why the process requires a proper understanding of PCB construction.

To ensure a quality solder joint, it is important to follow several guidelines. First, it is important to check the alignment of the printed board. Make sure that the print is properly aligned before applying the solder paste. Second, clean the stencil bottom regularly. Third, reflow soldering can result in a tombstone effect, otherwise known as the Manhattan effect. The tombstone effect is caused by force imbalances during the reflow soldering process. The end result looks like a tombstone in a cemetery. In reality, the tombstone effect is an open circuit on a defunct PCB.

During the preheat stage, a small portion of the solder paste can gasify. This can cause a small amount of solder to leave the soldering pad, especially under chip components. In addition, melted solder paste may push out under sheet-type resistor-capacitor units.

Wave soldering

PCB assembly process defects, including tombstoning, occur in a variety of ways. One of the main causes is inadequate soldering quality. Poor soldering results in cracks that appear on the surface of discrete components. These defects can be easily corrected with rework, although they can create a wide range of problems in the assembly process.

PCB manufacturers need to be aware of these defects to prevent them from occurring in the production process. These defects may be hard to detect, but different technologies and methods can help detect them and minimize their impact. These methods allow manufacturers to prevent soldering defects before they occur and help them produce high-quality products.

Stencil thickness

PCB pseudo-soldering can be caused by a number of factors. For example, an incorrect stencil can lead to over-applied solder paste on the components. Moreover, a poorly shaped stencil can result in solder balling or discrete deformities. These issues can be resolved by reducing the thickness of the stencil or the aperture size. However, these steps should be done with caution because even the slightest undersizing can lead to major problems in later PCB assembly stages.

PCB pseudo-soldering can be prevented by properly applying flux. Flux is a thixotropic agent that makes solder paste have pseudo-plastic flow characteristics. This means that it will reduce in viscosity when passing through the stencil’s apertures, but will recover once the external force is removed. The amount of flux used in solder paste should be eight to fifteen percent. Lower values will result in a thin solder film, while higher ones will cause excessive deposits.

Squeegee pressure

PCBA pseudo soldering, also known as cold soldering, is an in-between stage of the soldering process in which a portion of the board is not fully soldered. This can compromise the quality of the PCB board and affect its circuit characteristics. This defect may result in the scrapping or disqualification of the PCB board.

To control the squeegee pressure can solve the problem of pseudo soldering. Too much pressure will smear the solder paste and cause it to spread across the PCB’s flat surface. Alternatively, too little pressure will cause the solder paste to scoop up into larger apertures, causing the PCB to be covered with too much paste.