Application of BPDA/PDA Polyimide Films in Multi-chip Modules (MCM).

Abstract

Polyimides are widely used as dielectrics in high density multi-chip module (MCM) wiring systems in order to adjust the thermal expansion between LSI chips and substrates. In these MCMs, Copper is commonly used for vias which interconnects different layers. In these structures, there are some drawbacks which adversely affect the multi-layer wiring system. Among them, a major problem is that in order to get a high wiring density, a large number of vias with a very small via diameter have to be created. However, if there are large number of vias, due to the Z-directional thermal expansion mismatch of Cu and the dielectric, stress concentrated around vias leading to fracture and crank formation in the dielectric. Therefore, in this paper, in order to find a promising dielectric material, to the utilized in MCMs, the Z-directional coefficient of thermal expansion (CTE) of polyimide films prepared with different processing conditions was investigated. The Z-directional CTE of the films was measured by the laser interferometric technique.