Requirement
High Temperature
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What is high melting point solder
Most popular lead-free solder alloy is SAC305(Sn/3Ag/0.5Cu) and its melting point is 217~219˚C. However, requirements in specification become so versatile that a demand for high melting point solder is increasing. Most of high-melting point solder alloy’s composition is Sn/Sb base.
e.g.
・Sn/5Sb 238~241℃
・Sn/10Sb 242 ~256℃

Market demand
Traditionally, leaded solder alloy Sn5/95Pb (melting point of 300~314˚C) has been the most used high melting point solder alloy. Today, to comply to biological and environmental concern, lead-free solder technology has advanced. As the lead-free solder alloy technology advances, demand for high melting point solder alloy composition has been increased.
Example of lead-free high melting point solder alloy application
To prevent re-melting
Prevent component falling off the PCB in 2nd reflow in a case of double-sided PCB. Reflow peak temperature of SAC305 is 240~250˚C. Suppose SAC305 solder paste is used in soldering a double-sided PCBs. Solder joint formed in 1st reflow could re-melt in 2nd reflow and the soldered component could fall off. By using a Sn/Sb based solder paste in 1st reflow and SAC305 in 2nd reflow, melting point will be so different that the Sn/Sb solder joint will not re-melt and the soldered components will not fall off.
Use of a high-melting point solder alloy by module manufacturers for embedded passives is increasing as their products so that their products can be re-reflowed at their customers.

Increasing junction temperature
Junction temperature requirement is ever-increasing. Sometimes melting point as high as SAC305 is not sufficient. By using Sn/Sb- type solder alloy, operation under high-temperature environment can be ensured.
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