Hermetic sealing is one of packaging technique to demonstrate MEMS process. Hermetic sealing prevents moisture and gas in air enter inside of package and isolates device from atmosphere. In this study, as Pb-free solder materials suitable for hermetic sealing, Sn-2.8Ag-20In, Sn-10Bi-10In solder materials are chosen. Melting temperature of these two solder is within range of 180~190℃, so step soldering is possible. To choose final one solder alloy, several kind of experiments and tests are done. After reaction solder with UBM (Ni-3㎛, Au-1.5㎛), Intermetallic compounds formd inside of solder and interface between solder and UBM. IMC formed inside of solder are $Ag_2In$, $AuIn_2$ in SnAgIn solder and BiIn, $AuIn_2$, $AuSn_4$ in $Sn_{10}Bi_{10}$ In solder. IMC formed in interface part is $Ni_3Sn_4$ phase in both solder. $AuSn_4$ phase is formed only in SnBiIn solder. Indium content in solder material involves in formation of $AuSn_4$ in SnBiIn solder. Formed IMC is analyzed thermodynamically. At interface part between solder and UBM, $Ni_3Sn_4$ phase are observed, its growth kinetic with time and temperature is investigated. The growth rate of $Ni_3Sn_4$ is faster in $Sn_{10}Bi_{10}$ In solder because diffusion coefficient of Sn in SnBiIn solder is larger than that in SnAgIn solder. In shear strength test, shear strength value of both solder materials is similar to each other because fractured part of solder is interface between solder and $Ni_3Sn_4$. In wetting angle test, wetting angle of SnBiIn solder is smaller than that of SnAgIn solder. After bonding, large void In SnBiIn solder are observed. Through those tests SnAgIn solder is chosen to apply to real package. Optimized conditions are selected in based on the results of hermeticity test and shear strength test. Through reproducibility test and reliability test, High Temperature Storage test at 120℃optimized conditions are estimated.
