Isotropically conductive adhesives for high power electronics applications

A lot of research effords have been carried out to investigate and improve mechanical and electrical properties and reliability of electrically conductive adhesive (ECA) materials. A few of the studies have been directed towards evaluating ECAs for high power electronics applications. The objective of this study was focused on evaluation and characterization of isotropically conductive adhesives (ICAs). Three commercial silver-filled epoxy ICAs, one formulated silver-filled epoxy ICA in this study, and a 96.5Sn3.5Ag solder paste as reference were used as interconnecting materials. The ICAs were stencil printed on ceramic substrates and components with Sn- or Ag/Pd-plated terminations were mounted by pick-and-place equipment. ICA joints were cured by reflow process. Mechanical and electrical properties of the joints were measured. Temperature cycling (-40 to 125 degreesC, 300 cycles), heat storage (125 degreesC, 550 h) and humidity test (85 degreesC/85% RH, 550 h) were performed to assess reliabilities of the joints. Microstructures of the joints were observed by optical microscopy and scanning electron microscopy (SEM). The results indicated that most of the evaluated commercial and formulated ICAs were capable to carrying 6A current in linear behavior. The metallization of component terminations strongly affected performances of the ICA joints. The ICAs tested in this study had very good shear strength, especially ICA C. Postcure is important to achieve the possibly better performance of the ICAs. Two ICAs tested in this study showed possible signs of silver migration and further investigations are needed, to clarify this point.