How to stir correctlyLead-free solder paste? Many people (or the industry generally believes) believe that solder paste stirring is to evenly mix the solder paste and solder powder in the solder paste. In fact, the stirring of solder paste is to obtain the appropriate printing viscosity,We know that due to its certain thixotropy, the actual viscosity of solder paste during the printing process is different from that in its static state,The best printing effect of solder paste is achieved within a certain range of viscosities,If the solder paste is printed directly without stirring, its viscosity will be too high. The first piece or the first few pieces will have a series of problems such as poor tin discharge, lack of rolling property, and sticking to the scraper,Today, the editor of JJY will talk about the correct techniques for stirring:

Good solder paste will maintain a stable viscosity during the printing process. Such solder paste will not have a significant impact on viscosity even if it is stirred for a long time. However, during the stirring process, the solder paste will heat up, thereby affecting the service life of the solder paste.

For some solder pastes, their viscosity will gradually decrease during the printing process. Besides the aforementioned effects, excessive stirring time may cause the viscosity of the solder paste to drop, thereby affecting its usability.

Some solder pastes have a higher viscosity during the printing process. This is because the solvents in them evaporate too quickly. If the solder paste is stirred for too long, it will only affect its service life.

If the solder paste stirring is manual, it is generally done at3-5Minutes, automatic stirring1-3It only takes minutes. The function of stirring, apart from the well-known goal of making the tin powder and flux bond tightly and evenly, is just what we aim to achieve. However, during the stirring process, there will be an energy conversion action, that is, mechanical energy is converted into thermal energy. Stirring for too long will promote the evaporation of flux, especially for those that have already warmed up at room temperatureOKThe solder paste should not be stirred for a long time either. I did this when I was working at FoxconnDOEFor experiments, the stirring time should not be too long. If it is urgent to use solder paste that has not been fully warmed up, mechanical automatic stirring can be adopted5Minutes are combined with room temperature recovery1The same effect is achieved in a small time, but due to the use of abnormal means, the moisture in the solder paste is more than normal, and passing through the furnace will have an impact.

If the lead-free solder paste has just been taken out of the refrigerator or freezer, it must be warmed up at room temperature4Stir for more than an hour. When stirring, the surrounding environment must be kept clean, free from strong winds, dust, etc.

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