Formulation and Electrical and Mechanical Properties of Anisotropic Conductive Adhesive Pastes

摘要

There has been a steadily increasing interest in using electrically conductive adhesives as interconnecting materials in electronics manufacturing. Simple processing, low processing temperature and fine pitch capability are the major advantages of conducting adhesive joining technology. Tin/lead solder connection technology is widely used in today's electronics manufacturing. Lead is a toxic metal element, and is a well-known hazard to human health. Lead-free interconnecting materials are urgently needed and polymeric conductive adhesives are likely one of the best alternatives for tin/lead solders. A new and innovative connection technology geared towards achieving increased functionality at a lower total system cost, is anisotropic conductive adhesive (ACA) interconnection. ACAs, when used for flip chip assembly, provide electrical as well as mechanical interconnections for fine pitch applications. These conductive adhesives conduct only in the Z-direction (perpendicular to the plane of the board) while electrical isolation is maintained in the X-Y plane. The conductive particles used include pure metals such as gold, silver or nickel, or metal-coated particles with plastic or glass cores. The fine-pitch, and low processing temperature capability are the primary reasons for the growing use of ACAs. In the present study, several ACA pastes were formulated which consist of diglycidyl ether of bisphenol F or diglycidyl of bisphenol A as polymer matrix, imidazoles as curing agents, and different sizes of silver powders or gold-coated polymer spheres as conductive particles. The curing profile and thermal stability of the pastes were evaluated using Differential Scanning Calorimetry and ThermoGravimetric Analysis. Results of the tests of electrical and mechanical properties, and reliability using the pastes as interconnection material are reported.