PCB Technical - Causes of poor PCB soldering

Causes of poor PCB soldering

The factors that cause poor PCB soldering mainly come from two aspects: the circuit board factory and the placement factory.

1. Storage environment and transportation: This is a process between the circuit board factory and the placement factory. There is very little inventory of ordinary circuit boards, but usually the inventory requires the storage environment to be dry and humid, and the packaging is complete. During transportation It is best to handle with care, and it is not allowed to store for a long time if the vacuum package is damaged. The theoretical storage time of the spray tin plate is one month, but the best time for soldering is within 48 hours. If the storage time is more than one month It is best to return to the circuit board factory to use a special potion for cleaning and to bake the board.

2. The operation is not in accordance with the operating specifications at the time of shipment: the circuit industry is a workshop environment, and the staff standard operation requirements are particularly strict, especially the chemical reaction environment is required in the production of circuit boards, so no impurities are allowed to penetrate After the tin spraying process on the board is completed, the subsequent series of operations require employees to wear anti-static gloves. Because finger sweat or stains will directly touch the surface, it will cause surface oxidation. If it causes defects, it is difficult to be found, and it is irregular. It is difficult to show the performance of the test, the test and the tin experiment.

3. Welding defects caused by warping: circuit boards and components warp during the welding process, and defects such as virtual welding and short circuit due to stress deformation. Warpage is often caused by the temperature imbalance between the upper and lower parts of the circuit board. For large PCBs, warping may also occur due to the weight of the board itself. The ordinary PBGA device is about 0.5mm away from the printed circuit board. If the device on the circuit board is relatively large, it will return to its normal shape as the circuit board cools down, and the solder joints will be located under the stress for a long time. If the device is raised 0.1mm is enough to cause a virtual weld and open circuit. For special products, the yin and yang jigsaw of the circuit board factory can be required to reduce warpage, or it is best to use a suitable size imposition, which cannot be too large or too small.

4. The source of tin for incoming materials: For material procurement, some circuit board factories blindly seek to reduce costs. When using tin sprayed raw tin, the procurement industry recycles tin or sources of unstable content, usually with extremely low unit prices. Circuit board factories may have such a risk probability, so it is best for everyone to choose suppliers carefully.

5. The tin furnace used for tin spraying is not cleaned up on time: the on-time maintenance of the tin furnace is particularly important. Because the tin spraying is a vertical cycle process, the circuit board surface will be under strong pressure, and the solder mask is not dry and the characters are not firm. The board will fall off due to impact, deposit in the furnace, and evaporate at high temperature. If it is not cleaned for a long time, it will cause surface adhesion.