This study illustrates test results and comparative literature data on the influence of isothermal aging and thermal cycling associated with Sn-1.0Ag-0.5Cu (SAC105) and Sn-3.0Ag-0.5Cu (SAC305) ball grid array (BGA) solder joints finished with ENIG and ENEPIG on the board side and ENIG on the package side compared with ImAg plating on both sides. The resulting degradation data suggests that the main concern for 0.4 mm pitch 10 mm package size BGA is package side surface finish, not board side. That is, ENIG performs better than immersion Ag for applications involving long-term isothermal aging. SAC305, with a higher relative fraction of Ag3Sn IMC within the solder, performs better than SAC105. SEM and polarized light microscope analysis show cracks propagated from the corners to the center or even to solder bulk, which eventually causes fatigue failure. Three factors are discussed: IMC, grain structure, and Ag3Sn particle. The continuous growth of Cu-Sn intermetallic compounds (IMC) and grains increase the risk of failure, while Ag3Sn particles seem helpful in blocking the crack propagation.

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This paper reports an all-quartz high accuracy MEMS absolute pressure sensor based on high Q double-ended tuning fork (DETF) resonator, which is suitable for application in automotive, petroleum, meteorological, aerospace and spacecraft field. etc. The main parts of the MEMS pressure sensor, including the DETF resonator, diaphragm and back cavity structure, are all fabricated by quartz crystal using MEMS process. These pieces are bonded together as 'sandwich' structure to form the absolute pressure sensing unit using glass paste under low temperature and vacuum condition. This process could effectively eliminate the thermal stress effect and form the reference vacuum cavity. The experimental results show that the quality factor of the DETF resonator is up to 61000, the sensitivity is up to 7.35Hz/kPa in the operating range 0~250kPa, the pressure error is only 0.021%FS over the temperature range -40 ~+60 .

This paper reports a novel piezoelectric quartz crystal double-ended tuning fork (DETF) resonator with vibration attenuation structure, which is suitable for high resolution force sensing. The DETF resonator was designed to work in the fundamental flexure mode, and manufactured along the Y direction based on the Z-cut quartz crystal wafer using photolithographic and anisotropic chemical etching of quartz crystal. The resonance frequency of the DETF resonator is 39.1KHz. Vibration amplitude of the DETF resonator was measured and the experimental results show that vibration amplitude of the joint of DETF resonator is almost three orders of magnitude lower than that of midpoint of DETF, and the quality factor is up to 7750 at ambient condition and 59600 in vacuum, respectively.

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