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          Causes of bad tin on PCB tin surface

          2021-07-17 268

            Circuit board manufacturers summed up on the circuit board tin surface tin bad several ideas, we can refer to, hope to help us. The main factors of PCB bad soldering are from PCB Factory and SMT factory

            1. Storage environment and transportation: This is the link between the PCB manufacturer and the SMT factory. Generally, the PCB is rarely in stock. However, the general inventory requires that the storage environment should be dry and humid, and the packaging should be intact. In the process of transportation, it is required to handle it with care. It is not allowed to store the damaged vacuum package for a long time. The theoretical storage time of tinplate is one month, However, the best time for solderability is within 48 hours. If the storage time is more than one month, it is recommended to come back to the PCB Factory to clean up and bake the PCB with special liquid medicine. Baking parameters 150 ° 1 hour

            2. The operation during delivery was not in accordance with the operation specifications: the line work is extremely strict to the workshop environment and the standard operation requirements of the employees, especially the chemical reaction environment is required in the production process of the circuit board, so the entry of impurities is not allowed. After the tin spraying process of the board is completed, the subsequent series of operations require the employees to wear anti-static gloves, Because finger sweat or stains directly touch the surface, it will form surface oxidation. It is very difficult to find if the formation is bad, and it is irregular. It is difficult to show in the test and tin experiment.

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            3. Welding defects caused by warping: warping occurs in the welding process of circuit board and components, which leads to false 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 a large PCB, warping will also occur due to the weight drop of the board itself. A common PBGA device is about 0.5mm away from the printed circuit board. Assuming that the device on the circuit board is large, the solder joint will be under stress for a long time as the circuit board returns to its normal shape after cooling down. Assuming that the device is raised by 0.1mm, it is enough to cause false soldering and open circuit, Neither too big nor too small.

            4. Source of tin for incoming materials: as for material purchase, some circuit board factories blindly pursue cost reduction. When using the original tin sprayed with tin, they recycle tin in the purchase work. Maybe there is an unstable supply. Generally, circuit board factories with extremely low unit price may have such a risk. It is suggested that we choose suppliers carefully.

            5. Tin furnace for tin spraying is not cleaned up on time: timely maintenance of tin furnace is very important, because tin spraying is a process of vertical circulation. Under strong pressure, the PCB surface will fall off due to impact on those boards whose solder resist is not completely dry and the characters are not strong. They will deposit in the furnace and form external adhesion through high temperature evaporation.

                The article comes from:http://www.marysbrideandformals.com

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