The difference between high temperature solder paste and low temperature solder paste

Solder paste is one of the indispensable materials in the PCB soldering industry. Solder paste is divided into lead-free solder paste and leaded solder paste. There are high-temperature solder paste and low-temperature solder paste in lead-free solder paste. China SMT processing plant SYS Technology introduces the difference between high temperature solder paste and low temperature solder paste:

The melting point of common solder paste is 138° (low temperature) and 217° (high temperature). The low temperature is composed of tin and bismuth, and the high temperature is composed of tin, silver and copper. For LEDs products, we still recommended to use high-temperature lead-free solder paste, which has high reliability and is not easy to be cracked. There are also SMT chip manufacturers that use solder paste with a melting point of 183°, and the ratio of tin, silver, and copper is different from the melting point of 217°.

The melting point of pure tin is about 230°C. Generally speaking, the melting point of alloy (a mixture of two or more metals) is lower than that of elemental metal, and the melting point is different depending on the type and content of the alloy. The solder paste will be mixed with different additives according to different requirements to make different types of solder paste, so the melting point will also be different.

1. Composition: High temperature solder paste is generally composed of tin, silver, copper and other metal elements, while low temperature solder paste is composed of tin and bismuth.

2. Melting point: high temperature solder paste is composed of tin, silver and copper, low temperature is tin bismuth, low temperature melting point is 138, and high temperature melting point is 210-227.

3. The difference between reflow soldering: most of the low temperature solder paste is used in the second reflow of the double-sided reflow soldering process, because the if first reflow surface has larger components, and the same melting point is used for the second reflow, it is easy to cause the large devices on the first reflow surface (the second reflow is inverted) to be de-soldered or even fall off. Therefore, the low temperature solder paste is generally used for the second reflow, and when it reaches the melting point, the solder on the first reflow surface will not melt twice.

4. Application difference: after adding Bi to low temperature solder paste, its melting point temperature will be greatly reduced, and the composition of bismuth is also relatively brittle, generally only used for static products, normal application is for the LED field; high temperature solder paste has higher reliability and is not easy to de-solder and crack, the fields of application of will be more extensive.

5. Different formula maturity: The formula of high temperature solder paste is relatively more mature, with stable ingredients and moderate wettability, the formula of low temperature solder paste has lower maturity, unstable ingredients, easy to dry, and poor viscosity retention.