Alumina-based die attach and encapsulation for high-temperature (300oC to 500oC) electronic packaging were investigated. The alumina paste material comprises of aluminum dihydric phosphate as a binder and alumina powder as a filler with embedded nano aluminum nitride and nano-silica powders to promote its curing process, reduce its curing tension, and increase its bond shear strength. The chip-to-substrate bond strength was enhanced and met the MIL-STD-883 2019.9 requirements for die-attach assembly. Its encapsulation property was improved with fewer cracks compared to similar commercial ceramic encapsulants. The die-attach material and encapsulation properties tested at 500°C showed no defect or additional cracks. Thermal aging and thermal cycling were carried out on the samples. XPS analysis revealed a higher oxygen bonding percentage for the 10% nanosilica ceramic sample than the samples with no nano-silica. XRD peak broadening is largest for the 10% nano-silica ceramic which indicated smaller crystallite sizes. The smaller crystallite size for the 10% nanosilica sample introduces a larger microstrain to the alumina crystal structure. FTIR revealed the presence of alumina-silicate bonds on these samples with the largest amount present in the 10% nanosilica samples. Si-O and Al-O bonds were observed from FTIR on nanosilica samples especially the higher than 10% nanosilica samples. SEM and EDX results showed a uniform bond line for the 10% sample and uniform material distribution.

An electronic packaging technology that survives the simulated Venusian surface temperature of 465°C and 96 bar pressure in carbon dioxide (CO2) and nitrogen environments, without the corrosive trace gases, was developed. Alumina ceramic substrates and gold conductors on alumina were evaluated for electrical and mechanical performance. The most promising die-attach materials are thick-film gold and alumina-based ceramic pastes. Alumina, sapphire, silicon, and silicon carbide dies were attached to the alumina substrates using these die-attach materials and exposed to 96 bar pressure in a CO2 environment at 465°C for 244 h. The ceramic die-attach material showed consistent shear strengths before and after the test. An alumina ceramic encapsulation material was also evaluated for thermomechanical stability. The devices on the packaging substrates were encapsulated by a ceramic encapsulation with no significant increase in cracks and voids after the Venusian simulator test. Wire pull strength tests were conducted on the gold bond wire to evaluate mechanical durability before and after the Venusian simulator exposure. The average gold bond wire pull strengths before and after exposure were 5.78 g-F and 4 g-F for 1-mil gold bond wires, respectively, meeting the minimum MIL-STD-885 2011.9 standard. The overall wire bond daisy chain resistance change was .47% after the Venus simulator test, indicating a promising wire bond integrity. A titanium package was fabricated to house the ceramic packaging substrate and a two-level metalized feedthrough was fabricated to provide electrical interfaces to the package.

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