Glass as a Substrate for High Density Electrical Interconnect

The high volume production of substrates able to support high density interconnection is becoming increasingly difficult as the pitch of devices continues to decrease. An important issue is the alignment of microvias and pads which is made particularly challenging by the dimensional instability of traditional organic substrates. In this work, glass has been investigated as an alternative substrate material. Glass offers potential advantages including: electrical insulation, dimensional stability, thermal expansion similar to Si and optical transparency. This paper examines manufacturing processes for the preparation of substrates built up from 50 to 100 mu m thick glass sheets. Excimer laser machining was used to form microvias and tracks in the glass which were metallised using electroless plating methods. Using a photoresist layer during the laser machining process helped to reduce debris on the glass surface and could be used to direct the subsequent deposition of electroless copper or nickel such that circuit patterns could be created. Lamination of the thin glass sheets was investigated using direct glass to glass bonding and through the use of an intermediate layer. A method for the combination of these techniques to create multilayer substrates is proposed.