MEMS Packaging Solder Selection
2022-06-24
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MEMS Packaging Solder Selection
Micro-electromechanical Systems (MEMS) is a high-precision and small-size device. The current rapid development of wafer-level packaging reduces MEMS cost and size, which effectively promotes mass production. MEMS is difficult to package and has high requirements on packaging temperature and stress. In wafer-level packaging, solder is often used to connect chips to substrates and capping processes. One of the capping processes is to form a solder layer on the side of the packaged chip and the side of the capping wafer. The interconnection is achieved by reflow soldering. Fitech provides solder solutions for MEMS packaging. The mainstream packaging solders include:
Gold-tin solder paste is widely used in the hermetic packaging of MEMS sensors, which can effectively ensure the integrity of soldering. Gold-tin-tin paste has high thermal conductivity to reduce the thermal resistance of high-power lasers. The alloy composition and melting point of Fitech's gold-tin solder paste (FH-280) are Au80Sn20 and 280℃, respectively. T3-T6 solder pastes classified by particle sizes are available. Gold-tin solder paste has excellent tensile properties, wetting, and oxidation resistance. The solder joints are corrosion-resistant and fatigue-resistant. Due to the property of gold-tin alloys, the use of flux is eliminated. The formed solder joints can be free of cleaning, avoiding damage to the device's accuracy. Compared with other types of solder paste, the price of gold-tin solder paste is high because of its gold content.
SnBiAg Series
Fitech's FL170 series is tin-bismuth-silver solder. The peak reflow temperature is 170℃, which is suitable for low-temperature soldering of components. Since wafer-level packaging requires the entire wafer to be packaged, the viscosity of solder should be stable to allow long-term online packaging. The solder joints produced are high strength. The low melting point allows multiple reflow soldering.
Tin-silver-copper SAC305 is also a commonly-used package solder with a melting point of 217°C. Fitech's SAC305 solder has outstanding electrical and thermal conductivity, high particle roundness, and narrow particle size distribution. It is suitable for ultra-fine-pitch packaging. Compared with the brittleness of tin-bismuth-silver solder paste, SAC305 can provide a strong solder joint reliability. Fitech's FWS-305L series can be used for laser soldering and has excellent water solubility.
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