Wafer level packaging has emerged as one of the promising solutions for hermetic packaging of MEMS devices. Detection of the level of hermeticity of the package is essential for reliability and design assessment of the devices. Traditionally, hermeticity has been tested using Helium based fine leak testing. However, there are limitations when this technique is used for the hermeticity detection of small volumes (< 10−3 cc) that are typical in wafer level packages. This paper reviews the helium fine leak test, its limitations and the influence of the different test parameters on leakage rate measurement are analyzed for wafer level packages with small cavity volumes. The results indicate a need for development of a new hermeticity measurement technique to achieve the measurement sensitivity required for wafer level packages.
Objective of this paper is to investigate the transient response of a PV module irradiated by an impulse light flash. The impulse flash with a waveform of 8/20 μs was considered. LTSpice was employed for the numerical simulation. Based on the numerical results, the short-circuit current and the electrical properties of some cell components (such as the diode, capacitance and inductance) are demonstrated and discussed. It is found that the irradiation by the pulsed flash causes not only the oscillation of the short-circuit current, but also the oscillation of voltage and current of cell components, depending both on the capacitance C of the PV cell and on the inductance L of wiring and cables. It is also found that, under a certain condition of L and C, the diode voltage becomes negative; namely, application of the large reverse voltage to the cell is pointed out. It is concluded that the response of the PV module against the pulsed photo-current is composed of two sequential stages; the first stage is a charging stage of C by the pulsed photo-current, and the next stage is a discharging stage of C. The latter stage causes a damping oscillation of short-circuit current.
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