Use of solder mask as a protective coating for radiation detector
A radiation detector is described having a semiconductor substrate with opposing front and rear surfaces, a cathode electrode located on the front surface of said semiconductor substrate, a plurality of anode electrodes located on the rear surface of said semiconductor substrate and a solder mask disposed above the anode electrodes. The solder mask has openings extending to the anode electrodes for placing solder in said openings.
1. A method of forming a solder mask on a radiation detector comprising the steps of:
providing a radiation detector comprising:
a semiconductor substrate having front and rear surfaces;
a cathode electrode formed on the front surface of said semiconductor substrate; and
a plurality of anode electrodes formed on the rear surface of said semiconductor substrate;
forming a solder mask layer directly on the anode electrodes such that said solder mask forms an insulating layer between said plurality of anode electrodes;
patterning the solder mask layer to form openings extending to the anode electrodes;
forming an insulating material on side walls of the substrate;
forming a shielding cathode over the insulating material and over side walls of the substrate without making physical contact with the side walls of the substrate; and
forming a portion of a solder mask over the shielding cathode.
2. The method of claim 1 wherein the solder mask is in direct contact with interpixel portions of the semiconductor substrate located between the anode electrodes and the solder mask forms a protective coating for the radiation detector.
3. The method of claim 1 wherein the semiconductor substrate comprises CdZnTe or CdTe.
4. The method of claim 1 wherein:
the openings expose only a portion of a surface of each anode electrode; and
the anodes electrodes are in pixilated configuration.
5. The method of claim 1 wherein the solder mask comprises an epoxy.
6. The method of claim 1 wherein the step of patterning the solder mask comprises selectively exposing solder mask to radiation to cross link or uncross link selected portions of the solder mask and removing uncross linked portions of the solder mask.
7. The method of claim 1 further comprising forming solder balls in said openings and electrically connecting the solder balls to a printed circuit board.
8. The method of claim 1 , wherein the steps of forming the solder mask layer directly on the anode electrodes and forming a portion of the solder mask over the shielding cathode occur during a same deposition step.
9. The method of claim 1 , wherein the steps of forming the solder mask layer directly on the anode electrodes and forming a portion of the solder mask over the shielding cathode occur during different deposition steps.