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Preparation method and precautions of lead-free high temperature solder paste

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Update time : 2023-01-04 14:43:25
Process control and production methods when using lead-free solder paste. Nowadays, soldering of electronic products is an important production link. Currently, lead-free solder paste products are used. There are two types of products, low and high temperature, and they are also called lead and lead-free. , each of which is a different production method and control, the following small series of solder paste manufacturers will first introduce the production method of high-temperature solder paste.
Semiconductor devices working at high temperatures, especially power device LED packaging, high-density integrated circuit packaging, and the assembly of some precision integrated circuits, require the second or even third reflow soldering process to use high-lead solder paste for soldering. However, lead and its compounds are extremely harmful to the human body and pollute the environment.
The production process of the flux in the existing leaded and lead-free solder paste needs to be heated at a temperature of 100-130°C or even higher, so that the rosin resin reaches a molten state and dissolves into organic solvents (such as polyols, ethers, etc.) etc.). Various powdery activators (binary to polybasic organic acids) are also dissolved into the solvent at this temperature. After the mixture is completely miscible, cool to room temperature for use. The advantage of this type of process is that the raw materials dissolve quickly and the production time is short (generally 1 to 1.5 hours). However, the disadvantage is: because the production temperature is high, it not only causes the volatilization of the solvent, but what is worse: let all kinds of The valuable active components release activity at 100-130°C, decompose active ions in advance, and react with other components at this temperature, greatly losing the fluxing activity of the finished flux, thereby reducing fluxing performance and use efficiency. Therefore, reducing the production temperature of flux is the key to ensure the performance of flux. At present, the industry mainly reduces the preparation temperature of the flux by replacing the ingredients of the formula. For example, a halogen-free flux for tin-bismuth-based lead-free solder paste invented by the Chinese patent CN10485871A has a melting point of 138°C. However, during the preparation process, The temperature was as high as 180°C, which eventually resulted in the deactivation of a large amount of material.
The lead-free high-temperature solder paste is characterized in that it includes the following raw materials in parts by weight: 10%-15% of paste and 85%-90% of tin powder;
The paste includes the following raw materials in parts by weight: 45%-50% of solvent, 30%-35% of resin, 5%-8% of active agent, 1%-2% of stabilizer, 1%-2% of release agent, Accelerator 1%-2%, thixotropic agent 2%-3%.
What is the process control when using high-temperature solder paste? Let's take a look:
Strictly use the solder paste within the validity period. The solder paste is stored in the refrigerator on weekdays. It is required to be placed at room temperature for about 4 hours before use (this part is also called thawing) before it can be used. Determine whether the quality is acceptable;
Before production, the operator uses a special stirring rod to stir the solder paste to make it uniform, or stirs it with an automatic mixer, and regularly uses a viscosity tester to test the viscosity of the solder paste;
After printing the first printing board or equipment adjustment on the same day, the solder paste thickness tester should be used to measure the printing thickness of the solder paste. The test points are selected at 5 points such as the top, bottom, left and right, and the middle of the test surface of the printed board, and the values are recorded. Requirements The thickness of the solder paste ranges from -10% to +15% of the template thickness;
During the production process, 100% inspection of the solder paste printing quality is carried out, the main content is whether the solder paste pattern is complete, whether the thickness is uniform, and whether there is any sharpening of the solder paste;
Clean the formwork according to the process requirements after the work on duty is completed;
After the printing experiment or printing failure, the solder paste on the printed board needs to be thoroughly cleaned and dried with ultrasonic cleaning equipment to prevent solder balls after reflow soldering caused by residual solder paste on the board when it is used again.
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