Area bonding conductive epoxy adhesives for low cost grid array chip carriers

This paper describes a new type of Z axis epoxy film adhesive, called a_rea b_onding c_onductive (ABC) epoxies, to replace solder and solder balls for surface mounting grid array chip carriers. The ABC adhesives are made by a low cost screen printing process, starting from customer-supplied artwork, so that the conductive epoxy regions are located only at the desired bond pad locations. Reliability data, presented for plastic and LTCC packages attached to FR-4 boards with these adhesives, show better resistance to thermal cycling and thermal shock than soldered packages. This paper also describes a new low cost copper lidded pad array chip carrier, called a Cu-PAC. This uses an ABC epoxy for die and for substrate attach. The Cu-PACs have the potential for major cost savings, size reduction and improved heat removal compared to present molded plastic grid array packages.