I believe that most PCBA processing plants often encounter some poor solder joints when PCBA soldering, and one of the problems is that the solder joints are sharpened. As the name suggests, the point of the solder joint is that the precision of the solder joint is not high, and the surface is pointed. The accuracy of the solder joints is not high, which means that the solder joints are not smooth, and the sharpening refers to the phenomenon that the solder joints are not well formed or have burrs and sharpness after welding. This situation is mainly caused by the poor liquidity of tin, and it also has a certain relationship with our parameter settings. The sharpening is mainly due to the excessively long welding residence time, which causes the flux to volatilize too fast, and the sharpening phenomenon occurs when the soldering iron tip is lifted. How can we effectively avoid this phenomenon? The following Sanjing will take you to understand the specific causes and solutions of the solder joints in PCBA welding. I hope it can be helpful to everyone!

The first reason is that the temperature of the PCB circuit board during the preheating stage is too low and the preheating time is too short, so that the temperature of the PCB and the components is low, and the components and the PCB absorb heat during soldering to produce a convex tendency. Therefore, the temperature of the PCB circuit board during the preheating stage cannot be too low, and the preheating time cannot be too short.

Secondly, when the SMT chip is soldered, the temperature is too low or the conveyor speed is too fast, so that the viscosity of the molten solder is too large. Therefore, the solder wave temperature of the SMT patch should be controlled between 250℃±5℃, and the soldering time is 3~5s; when the temperature is slightly lower, the speed of the conveyor belt will be slower.

Third, the wave crest height of the electromagnetic pump wave soldering machine is too high or the pin is too long, so that the bottom of the pin cannot touch the wave crest. Because the electromagnetic pump wave soldering machine is a hollow wave, the thickness of the hollow wave is 4~5mm. Therefore, the peak height is generally controlled at 2/3 of the thickness of the printed board, and the lead forming of the plug-in component requires that the component lead is exposed to the soldering surface of the printed board by 0.8mm~3mm.

Fourth, the flux activity is poor. Therefore, the best solution is to replace the flux.

Fifth, the ratio of the lead diameter of the DIP plug-in component to the plug-in hole is not correct, the plug-in hole is too large, and the large pad absorbs a large amount of heat. The most suitable ratio of the lead diameter of the DIP interposing component to the insertion hole is that the lead diameter is 0.15~0.4mm smaller than the hole diameter of the insertion hole (the thin lead takes the lower limit, and the thick lead takes the upper limit).

The above problems are the most important factors that cause the solder joints to be sharpened. Therefore, we must make corresponding optimizations and adjustments to these problems in the SMT chip processing to ensure the yield of the products.