The solder bar is a bar-shaped tin solder, referred to as a tin bar for short. Solder bars are mainly used for wave soldering and dip soldering in SMT patch processing, and a small amount is used for flame brazing or electric soldering of large structural parts and long welds. The process of making solder bars is relatively simple, mainly including batching, smelting and casting processes. During the process, the degree of oxidation, the content of metal and non-metallic impurities must be strictly controlled, and the two parameters of melting temperature and pouring temperature have an impact on the quality of solder bars. larger.

1. The quality requirements of solder bars mainly include the following aspects

1. The strip surface is smooth.

2. Good fluidity and wettability during welding nugget.

3. Good mechanical properties.

4. The solder joints are bright.

5. Less oxidation residue.

2. Classification of solder bars

According to environmental classification, solder bars are divided into leaded tin bars and lead-free tin bars. Currently commonly used lead solder bars are: 63/37 solder bars (Sn63/P637) and 60/40 solder bars (Sn60/Pb40), commonly used lead-free solder bars are; tin-copper lead-free tin bars (Sn99.3 /Cu0.7), tin-silver-copper lead-free tin bar (Sn96.5/Ag3.0/Cu0.5) and 0.3 silver lead-free tin bar (Sn99/Ag0.3/Cu0.7) except the main elements In addition to tin, lead, copper, and silver, it often contains a small amount of other elements, such as nickel (Ni), antimony (Sb), zinc (Zn), bismuth (Bi), indium (In) and rare earths. These trace alloy elements in the solder bar have a great influence on the performance of the tin bar. For example, adding chromium can reduce the melting temperature of the solder bar and improve the wettability, but if the amount is too large, it will reduce the fatigue life of the solder joint and Properties, bismuth content is about 0.2% to 1.5%. Adding nickel can change the alloy structure and refine the grains, thereby improving the mechanical properties and fatigue life of the solder joints. Therefore, the solder bar needs to achieve an optimal balance in all aspects such as welding performance, melting temperature, strength, plasticity and fatigue life.

The tin content in the lead solder bar for wave soldering is 63%, the melting point is 183°C, and the working temperature is 230-250°C. The common composition of lead-free solder bars for wave soldering is Sn99.3/Cu0.7, the melting point is 227°C, and the working temperature is 270-320°C. According to the critical point of liquidus temperature, solder bars are divided into high-temperature solder bars and low-temperature solder bars. . The solder bar whose liquidus temperature is higher than the melting point of the tin-lead product at 183°C is a high-temperature solder bar. The high-temperature solder bar is a solder bar formed when a high proportion of silver, antimony, or Assembly of components that do not change during printed circuit board assembly. The solder bar whose liquidus temperature is lower than the melting point of the tin-lead eutectic is a low-temperature solder bar. The low-temperature solder bar is a solder bar formed by mixing, and, etc. Device assembly.

According to the classification of chemical properties, solder bars are divided into anti-oxidation solder bars and high-purity low-slag solder bars. The anti-oxidation solder bar has the characteristics of good anti-oxidation ability, high fluidity, strong weldability and very little scum when melting. At the same time, it also has the advantages of excellent wettability and solderability, full and uniform solder joints, and excellent welding effect. High-purity low-dross solder bar is composed of electrolytic tin, lead or tin-lead alloy. It is molded, cast or extruded, and has the characteristics of high purity, ultra-low slag and high wettability, and can be adapted to various SMT processing and welding processes