Aspects of electronic device packaging
For this work cordierite has been investigated as a possible substitute substrate material for alumina, with particular emphasis on its role in multilayer device packaging. By limiting the processing temperatures to below 1000oC, copper could be used as the conductor material. Milled glass powder was made into thin sheet form by a doctor blading technique and, once dried, the copper screen printed on top. After lamination and firing, the conductor was completely encapsulated by the cordierite matrix. Copper diffusion occ~red with metallic copper precipitating out although a small denuded zone was evident around the periphery of the conductor. This was due to compositional changes occurring there. Experiment showed that the effects of glass particle shape, average size and size distribution lead to deviation in the shrinking of compacts from the theoretical sintering curves. An unstable ~ phase was the first to appear on the glass particle surfaces although another, unidentifiable phase, was also found to exist during the very early stages of crystallization. This was followed shortly after by bulk crystallization of ~ cordierite in the remaining glass, possibly being aided by a prior phase separation. Further heat treatment lead to the transformation to a cordie rite and the formation of enstatite, the exact transformation temperature depending upon the minor oxide additives in the glass. At temperatures above ~10500C protoenstatite formed and lead to a general degradation in material properties. The benefit from having a cordie rite as the principal phase is a low dielectric constant (5.35) and loss angle (5 x 10-4), reasonable strength (130 MPa) and high resistivity (~1015 Qcm). This makes it a suitable replacement for alumina although its low thermal conductivity (~2 Wm-lK-l) is a drawback. By adjusting the MgO/A1203 ratio, the material could be expansion matched to that of silicon.