Temperature Behaviour of the Bowing of Multilayer Thick Film Substrates

The bowing of thick film substrates, wholly covered with copper pastes of the Du Pont base metal system DP 9922 and 9924, with one, four and ten layers has been measured from room temperature up to 700°C. It could be shown that the bowing does not, as expected, decrease uniformly with increasing temperature up to the softening point of the glass, but a change occurs in the curvature of bowing between about 80° and 100°C. By removing the copper layers the glassy interlayer could be investigated on the substrate. Its temperature behaviour is quite linear up to the softening point and the curvature is in contrast to that of the complete copper layer on the substrate. The superposition of the curvature of the metal and the glassy interlayer leads to the above‐mentioned change in the curvature of the complete copper layer. The deviation of the bowing that was found experimentally and that calculated by means of the plates theory, discussed in a previous paper, can therefore be explained by that change in the curvature and by a plastic deformation process in the copper. The values are caused by a reduction of stresses by plastic deformation in the metal during the cooling process. These results offer some possibilities for a reduction of the bowing of multilayer interconnection modules for use in hybrid microelectronics.