Solder mask encapsulation on CdZnTe surface for radiation detector applications

Cadmium zinc telluride (CZT) surface protection through chemical encapsulation is critical for making reliable pixellated radiation detectors. Epoxy based photoimageable solder mask has been found to be an effective coating material for protecting bare CZT surfaces. Solder mask coating has a couple of functions depending on surface areas coated, and on detector manufacturing and application processes. Firstly, solder mask applied on the pixellated anode surface with opening patterns on electrode pads could provide packaging guidance when conductive epoxy or solder ball is used for CZT substrate — printed circuit board (PCB) attachment. Secondly, solder mask provides excellent protection to CZT bare surfaces from mechanical scratching, moisture penetration, and chemical attack. In addition, solder mask provides excellent electrical isolation between interpixel gaps, anode to cathode edges, and between shielding cathode and semiconductor substrate. In this paper, gamma ray spectral responses and leakage current — voltage characteristics of CZT pixellated detectors encapsulated with solder mask were extensively studied. Solder mask coatings were applied on detectors with various shapes, sizes, and pixel patterns. Encapsulated detector showed stable and reliable performances. It was concluded that epoxy based solder mask was an excellent encapsulating material for CZT radiation detectors.