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The types of solder paste using in SMT process Written by HC AUTOMATOIN / Read 226 times

1. Leaded solder paste and lead-free solder paste                                                                                                                                                                                                             

     Lead solder paste contains lead in its ingredients, which is characterized by greater harm to the environment and human body, but it has good welding effect,
low cost, and high mechanical strength of solder joints. It can be used in some electronic products that do not require environmental protection. As the name
implies, lead-free solder paste does not contain lead in the ingredients. It is characterized by less harm to the human body and is an environmentally friendly
product. However, the mechanical strength of solder joints is lower than that of lead-based solder paste. At present, lead-free solder paste is mostly used in the
SMT industry. However, lead-free solder pastes generally contain trace amounts of lead, and the SMT industry requires that the lead-free lead content must be
reduced to a level below 1000ppm (<0.1%).


2. High temperature solder paste, medium temperature solder paste, low temperature solder paste


3. High temperature solder paste refers to the commonly used lead-free solder paste, the melting point is generally above 217°C. Common solder paste ingredients are Sn96.5/Ag3.0/Cu0.5 and Sn99Ag0.3Cu0.7;


4. Medium temperature solder paste, the commonly used lead-free medium temperature solder paste has a melting point of about 178 ℃. The characteristics of medium temperature solder paste are mainly the use of imported special rosin, which has good adhesion and can effectively prevent the collapse of printing solder paste. Common solder paste ingredients are Sn64/Ag1/Bi35;


5. The melting point of the low-temperature solder paste is 138°C. The low-temperature solder paste is mainly made of bismuth. When the component patch processing and welding cannot withstand the temperature of 200°C and above, the low-temperature solder paste is used for the soldering process, which can not withstand the protection. High-temperature reflow soldering solders originals and PCB, and is widely used in the LED industry. Common solder paste ingredients are Sn42/Bi58;


6. Particle size of Tin powder

The particle diameter of tin powder is mainly divided into three grades, No. 2 powder is 45 to 75 microns, No. 3 powder is 25 to 45 microns, and No. 4 is 20 to 38 microns. No. 2 powder is used for standard SMT processing devices with a pitch of 50mil. When the pitch is smaller than 30mil, No. 3 powder must be used. No. 3 powder is used for small pitch technology (30mil-15mil), when the pitch is 15mil or less, No. 4 powder solder paste will be the best. The more precise the product, the smaller the tin powder, but the smaller the tin powder, the correspondingly increase the oxidation area of the tin powder. In addition, the shape of the tin powder is round, which is beneficial to improve the quality of printing. The higher the difficulty of SMT chip processing products, the more important the selection of solder paste is. Only the solder paste suitable for product requirements can effectively reduce the quality defects of solder paste printing, improve the quality of reflow soldering, and reduce production costs.