What is a low-melting point solder alloy?

One of the most popular lead-free solder alloy used in general is SAC305 (Sn/3Ag/0.5Cu), and melting point is 217~219C. Nowadays, the market demands a low-melting point solder alloy with even lower melting point than SAC305. Among the low-melting point solder alloy compositions, Sn-Bi type solder alloys are being focused.
・Sn/58Bi melting point: 138˚C

Reflow setting temperature can also be 40~50˚C lower than SAC305, therefore, it is a soldering material that can contribute to energy-saving and CO₂ reduction (carbon neutral).

Market demand for low-melting point solder alloy

Today, SAC305 alloy is generally used in most of the soldering needs. However, growing trend for multi-layered and thin PCBs, and miniaturized and low-profile electric components, brought new issues: solder joint defect induced by PCB warpage, soldering components on low-heat resistant components on PET boards, or a need for additional soldering process for low-heat resistant electric component after the main soldering, etc. To solve these issues, low-melting point solder alloy is drawing attention as it is capable of mitigating PCB warpage, soldering low-heat resistant PCB and reducing a separate soldering process for low-heat resistant components.

Actual cases of low-melting point alloy use

Soldering low-heat resistant materials

Low-melting point solder alloy is used if using SAC305 alloy (217~219C) could exceed the heat resistance capacity of the components, such as ultraprecision components, plastic components, PET PCB, and other materials which has warpage concern during soldering, such as flexible printed circuits (FPC).

Soldering all additional components which needed a separate soldering process

Additional soldering process can be eliminated by being able to reflow components that are made of resin (connector, etc.) can be reflowed with other SMT components.

Cost reduction/ energy saving/ CO₂ reduction

By using low-melting point solder, materials with low heat resistance (electric components and PCB, such as paper phenolic board) can be used to reduce the material cost. In addition, temperature setting of the soldering equipment, such as reflow oven or wave soldering machine can be reduced, saving energy consumption and cost, and reduce CO₂ emission.