Analysis of Low-Temperature Indium Seals for Hermetic Packaging of Large-Area Photodetectors

The optimization of process parameters for sealing the sealing of large-area photodetector glass packages using low-temperature indium seals has been investigated in this report. Small scale 2.54×2.54 cm samples were used for experiments in order to gain an understanding of how the processing parameters will effect the seal integrity when scaled up to larger sizes such as 22×22 cm. First, substrates of B33 borosilicate glass were used for seal fabrication to validate that sealing indium to glass was indeed feasible and to study the effects of processing parameters on the integrity of the seal. Second, seals were made using glass substrates which were coated in an 80 wt% Ni/20 wt% Cr alloy (Nichrome A) to investigate its merit as an intermediate bonding layer to glass. Helium leak testing of the seals conclude that hermetic seals can be made using B33 glass in either the uncoated or NiCr-coated condition. The samples were also characterized by means of a lap shear test to evaluate the effect the applied load, load duration, and fabrication temperature played on the robustness of the joint. It was seen that increasing the applied load over the range of 890 to 2225 N leads to an increase in seal strength when using B33 substrates. Increasing the process duration over the range of 10 seconds to 60 minutes resulted in an increase in seal strength. Increasing the processing temperature from room temperature to 80 ºC increase in seal strength. However, indium began to over-flow from the edges of the substrates at 55ºC. For Nichrome-coated samples, an average increase of 54% in seal strength was seen when the applied load was increased from 1180 to 1558 N. Increasing processing time and temperature did not appear to have any effect on the seal strength of nichrome-coated samples. Aging of nichrome samples did not alter the integrity or hermeticity of the seals. Also, aged nichrome-coated seals were evaluated using Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) to identify if any new phases were present as a result of sealing. I