Diamond-a new high thermal conductivity substrate for multichip modules and hybrid circuits

Sandia National Laboratories is developing diamond substrate technology to meet the requirements of high thermal conductivity. Thin-film processes were developed and characterized to delineate conductor-resistor networks on free-standing diamond substrates having fine line gold conductors and low and high sheet resistivity resistors. Thin-film hybrid circuit technology was developed on CVD (chemical vapor deposition)-processed, polycrystalline diamond substrates having as-deposited surface finishes as well as those with polished surfaces. Conductors were defined by pattern plating gold and resistors were processed from sputtered tantalum nitride films which were deposited to sheet resistivities of 5 and/or 100 ohms per square. Resistor films on diamond substrates were evaluated for temperature coefficient of resistance (TCR), stability with time and temperature, and trimmability using YAG laser processing. Plated gold conductors were patterned on diamond to feature sizes of 25 microns and successfully tested for adhesion and bondability. Advanced YAG laser trimming techniques were developed to allow resistor trims on both low and high value resistors to within 1% of design value while maintaining required resistor stability