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 area bonding conductive (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 (Cu-PAC), which 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 (PGA) packages