Self-alignment feasibility study and contact resistance improvement of electrically conductive adhesives (ECAs)

With the driving force of "green" revolution in electronics industry, tremendous efforts have been put on looking for lead-free alternatives. Although lead-free alloys draw a lot of attention, their parasitic weaknesses, such as high processing temperature and surface tension, limit their application on thermally sensitive, flexible, non-solderable substrates and ultra-fine pitch size flip chip interconnection. Conventional electrically conductive adhesives (ECAs) have been widely used in surface mount and die-attach technologies for electrical interconnection and heat dissipation. Low processing temperature of ECAs is one of the major advantages over lead-free solders, which brings low system stress, simple manufacture process and the like. In order to improve the contact resistance of ECAs, the low melting point alloy (LMA) incorporating technology had been developed by our group. In this paper, the research thrust was concentrated on the LMA depletion method since re-melting LMA in ECAs can adversely affect the physical property. A differential scanning calorimeter (DSC) was used for the basic examination of depleting rate of LMAs in the typical ECAs. Cross-sectional morphology was investigated by scanning electron microscopy. A new curing process was designed to deplete the LMA in ECAs. Providing enough time for LMA to wet on the surface of silver and metal pad could improve the contact resistance on non-noble metal pad during high temperature and humidity test.