Author: G. Rinne Company: MCNC Date Published: 9/10/1996
Surface Mount International
Abstract: The activities at MCNC associated with the Flip Chip Technology Center (FCTC) will be described. One of the primary areas of development is bumping either on the existing I/O pattern, or a redistributed connection footprint. The bumping process is based on an electroplating method which provides added flexibility with respect to bump size and solder composition. Significant progress has been made in reducing process cost by means of innovative modifications which reduce the number of process steps and complexity. With the recent development of a method for redistributing perimeter I/O devices to area array using solder for the redistribution conductors, the cost of flip chip packaging for conventional devices has been dramatically reduced. Quality, reliability, and cost data for these new processes will be described with particular emphasis on Direct Chip Attach applications. Highlights of the process for both high lead and high tin solders will be shown, covering a range of sizes from 20 micron to 600 micron diameters. The process is currently being used for contract bumping and is available for licensing. In the area of assembly technology, MCNC has developed and is licensing a radically new fluxless, no-clean process which has shown considerable success with a variety of flip chip configurations. The process, called PADS (Plasma Assisted Fluxless Soldering) relies on a pretreatment which enables the subsequent solder reflow in inert , and even oxidizing ambients. Conventional mass production soldering tools can be used, just eliminating the flux dispense and flux cleaning steps, and adding the pretreatment step. Highlights of the applications studies will be presented. Examples will include eutectic tin/lead solder bumped flip chips joined in a nitrogen inerted belt furnace at 250 C to bare copper, direct chip attach (DCA) of 95/5 lead/tin bumps to eutectic dipped FR4 printed circuit boards, joining of 97/3 lead tin bumps at 350 C to Multilayer Ceramic MoNiAu, unique MEMS (Micro Electrical Mechanical Systems) devices joined with the dry fluxless process, and solder bumped flip chips joined to flexible circuits.