Ceramic coatings on package lids for radiation protection

A study was conducted to determine the feasibility of coating gold plated kovar lids with colloidally bonded aluminum oxide. Radiation that is incident on a gold plated lid generates a large number of photoelectrons. These electrons can enhance the damage to microelectronic devices and circuits (ICs). The primary purpose of the coating is to stop the electrons emitted from the lid that would otherwise increase the damage to the IC. A coating system consisting of {approximately}95 wt % alumina (0.5 {mu}m particles) and {approximately}5 wt % colloidal silica (10 nm particles) was developed. The coating was applied to the lids as an aqueous suspension which was then dried to form a porous coating. Coating processing conditions were optimized so that crack-free, uniform coatings with the required thickness ({approximately}80 {mu}m) could be consistently produced. Preliminary data have indicated that the coated lid can be attached to the IC package using current belt furnace sealing procedures. The adhesion and mechanical integrity of the coatings were evaluated by submitting coated lids to centrifuge and shock testing. Selected coatings successfully withstood the shock test and 85% were undamaged after being subjected to an acceleration of 30,000 g's. Several types of radiation tests were performedmore » to determine the effectiveness of the coating to stop electron penetration. Evaluation testing included gamma dose enhancement and X- ray induced photocurrent enhancement. The results for lids with coatings 80 or 150 {mu}m thick were compared with results for uncoated kovar and ceramic lids. 6 refs., 6 figs.« less