Analysis of the causes of PCBA solder detects

1. The solderability of the plate holes

If the solderability of the plate holes  may cause solder defects of PCBA, affecting the parameters of the components in the circuit, leading to the instability of the multi-layer board elements and inner line , causing the failure of the whole circuit function. The so-called solderability is the characteristics of the metal surface wetted by molten solder, also means that the metal surface forming a relatively uniform continuous smooth adhesion film.

The main factors affecting the solderability of PCB;

(1) The composition of the solder and the property of the solder. Solder is an important part of soldering process. Commonly used Low melting point eutectic metal like Sn-Pb or Sn-Pb-ag. Impurities should be controlled in a certain proportion to prevent the oxides from impurities melted by solder. White rosin and isopropanol solvents are generally used to help the solder wetting the surface of the broad plate by transferring heat and removing rust.

(2) The temperature and surface of metal plates also affect solderability. When the temperature is too high, the diffusion speed of solder is also higher, at this time the oxygenation of circuit board and the solder melted surface resulting in weld defects. Including tin beads, tin balls, broken circuits and so on.

2. PCBA solder defects caused by warping

The stress deformation also causes solder defects such as soldering joints and short circuits. warping is often caused by an imbalance in the temperature of the upper and lower parts of the board. For large PCBs, warping may occur due to the weight of the plate itself.  Ordinary components are approximately 0.5mm from the printed circuit board.when the circuit board returns to its normal shape by cooling down,  the solder joints will be stressed for a long time If the components on the circuit board is large.

3. PCB design affection

In the PCB design , when the circuit board size is large, soldering is relatively easy to control, but the printing line length, impedance increases, noise resistance is reduced, cost increases; when the circuit board size is tiny, cooling is hard, soldering is difficult to control.

Therefore,the PCB design must be optimized