Inkjettable conductive adhesive for use in microelectronics and microsystems technology
Ink jet is an accepted technology for dispensing small volumes of material (50 - 500 picolitres). Currently traditional metal-filled conductive adhesives cannot be processed by ink jetting (owing to their relatively high viscosity and the size of filler material particles). Smallest droplet size achievable by traditional dispensing techniques is in the range of 150 μm, yielding proportionally larger adhesive dots on the substrate. Electrically conductive inks are available on the market with metal particles (gold or silver) < 20 nm suspended in a solvent at 30-50 wt%. After deposition, the solvent is eliminated and electrical conductivity is enabled by a high metal ratio in the residue. Some applications include a sintering step. These nano-filled inks do not offer an adhesive function. Work reported here presents materials with both functions, adhesive and conductive. This newly developed silver filled adhesive has been applied successfully by piezo-ink jet and opens a new dimension in electrically conductive adhesives technology. The present work demonstrates feasibility of an inkjettable, isotropically conductive adhesive in the form of a silver loaded resin with a 2-step curing mechanism: In the first step, the adhesive is dispensed (jetted) and precured leaving a "dry" surface. The second step consists of assembly (wetting of the 2ndpart) and final curing.