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Reasons and countermeasures for yellowing and blackening of PCB solder paste soldering

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Update time : 2022-10-27 21:13:23
Most electronic circuit board manufacturers will encounter some problems more or less when using solder paste for soldering. For example, false soldering, false soldering, tin beading, sharpening, yellowing, blackening, etc.
Causes and Countermeasures of Solder Paste Yellowing
1. The surface of the PCB board is too wet: the PCB board will go through the drying process in the furnace during the production process. Due to the special circumstances, the humidity of the PCB board surface is too high, and it is easy to produce tin explosion when it comes into contact with the high temperature tin liquid during soldering. This will lead to yellowing of the PCB surface. When soldering solder paste, try to ensure that the PCB surface is relatively dry.
2. Temperature problem: When the abnormal color of the PCB surface after solder paste is soldered, it is generally related to the temperature. When the temperature of the solder is too high, the surface of the tin liquid will turn yellow. The temperature in the furnace is properly adjusted to ensure that the temperature is within the appropriate operating temperature range.
3. Too much rosin in the solder paste: The rosin is generally yellow or brown. When the rosin content in the solder paste is too much, the PCB circuit board will easily appear a light yellow after soldering. The role of rosin is to assist welding, but it is not the more the better. When selecting solder paste, you can first test the sample. If yellowing occurs, choose a solder paste with low content of rosin.
Causes and Countermeasures of Solder Paste Blackening
The blackening of solder paste is also a very common problem in the daily use of solder paste. The blackening of solder paste is mainly caused by problems in the soldering process and materials.
1. Reasons for the soldering process: When the solder paste is reflowed, if the temperature is too high and the heating rate is too fast, it is very easy to cause the solder paste to turn black, because the high temperature causes the solvent inside the solder paste to volatilize quickly, which leads to tin The tin powder in the paste is oxidized prematurely, and the soldered joints are blackened.
2. Material problems: some manufacturers will buy some cheap solder pastes in order to pursue low prices, and these low-priced solder pastes are not very strict in terms of material selection, and often use some tin powders that have been stored for a long time. The poor quality of these low-quality tin powders will lead to black solder paste solder joints.
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