What are the reasons for the blackening of PCBA pads?

The issue of blackening of PCBA solder joints is a relatively common defect in circuit boards, and there are many reasons for the occurrence of blackening on PCBA solder joints. However, it is usually caused by the following reasons:

1，Oxidation of Solder Joints:

If PCBA solder joints are exposed to humidity for a long time, oxidation reactions can occur on the surface, forming an oxide film on the solder joints and causing them to turn black. Therefore, it is essential to store PCBA in a dry environment and promptly vacuum package it to avoid prolonged exposure to air.

2，Welding Process Issues:

During reflow soldering or wave soldering, excessively high temperatures or prolonged soldering times can lead to oxidation and blackening of solder joints. This reaction is typically caused by exceeding the recommended temperature range for soldering materials. Therefore, it is crucial to follow the operating specifications during the soldering process.

3，Solder Material Issues:

Solder materials, including solder paste and solder bars, vary in quality. The use of poor-quality solder materials may release harmful substances and impurities, leading to blackening of the solder joints. Therefore, it is essential to avoid the use of low-quality solder materials.

4，Cleaning Issues:

Typically, when using flux, the board needs to be cleaned to remove residues. Failure to thoroughly clean the residues of the flux on the solder joints may lead to their degradation or carbonization at high temperatures, causing the solder joints to appear black. Therefore, timely cleaning after soldering is necessary.

5，Component Issues:

Poor-quality electronic components or improper materials for component pins can also result in solder joint blackening during soldering. Therefore, it is crucial to choose high-quality components and ensure that the plating quality and pin materials of the components are qualified.

These are the main reasons for the blackening of PCBA solder joints. Depending on the specific cause, corresponding improvement measures can be selected to effectively reduce the problem of PCBA solder joint blackening and improve product quality.