Low-temperature air-fireable glass-free metallic thick-film electrical conductor materials

Abstract

Low-temperature air-fireable glass-free metallic thick-film electrical conductor materials were developed for interconnections in electronic packaging. The thick film with composition (by weight) 96.60%Ag, 1.38%Cu, 0.28%Al, 0.35%Ti, and 1.39%Sn used Ti-Al as the active binder. After firing in air at 500∞C it exhibited low electrical resistivity (6.2 ¥ 10 -6 W·cm), good scratch resistance and strong bonding with the alumina substrate, with no pinholes. The firing caused complete melting of the particles in the film. Firing in argon rather than air degraded both electrical and bonding properties, due to the absence of oxygen, which helped to burn out the vehicle. The use of Ti rather than Ti-Al as the active binder resulted in holes in the thick film due to incomplete melting of the Ti-rich particles and also resulted in poor scratch resistance and weaker bonding to the substrate. Tin in the composition was important for promoting melting and protecting the active particles from oxidation during firing.

Burnout of the organic vehicle in an electrically conductive thick-film paste

“…22 The organic vehicle consisted of 40 wt.% ethyl cellulose and 60 wt.% di(ethylene glycol) butyl ether. The ratio of silver powder to the organic vehicle in the paste was 3:1 by weight.…”

“…Organic additives are widely used in ceramic slurry preparation (as in tape casting and gelcasting [1][2][3][4][5][6][7][8], green compact fabrication (as in powder metallurgy [9][10][11][12][13][14][15][16][17][18][19] ), thick-film materials development, [20][21][22][23][24] and other applications. [25][26][27][28][29] The ingredients are typically functional phases in the form of solids, and organic additives in the form of liquids, solutions, or suspensions.…”

“…Glass frit was absent, as it is not needed for glass-free pastes, which use minor metal ingredients, such as titanium, to provide bonding. 22 The effects of heating rate and interrupted heating on the burnout were also studied.…”

Comparative study of electrically conductive thick films with and without glass

“…14 The organic vehicle consisted of 60 wt.% ethyl cellulose and 40 wt.% di(ethylene glycol) butyl ether. The ether is a volatile solvent; ethyl cellulose is a solute dissolved in the ether for the purpose of increasing the viscosity and, hence, enhancing the suspension of the solid particles in the paste, in addition to improving the thermal stability of the paste.…”

“…A composite based on silver, containing titanium as the active component and exhibiting low electrical resistivity, was developed in previous work. 13,14 However, the advantages of air-fireable, glass-free thick films remain to be identified and elucidated. This work is a comparative study of thick film with and without glass.…”