OVERVIEW

Process steps for bonding have undergone significant changes since the 1960s and 1970s. Most processes then were manual or semiautomatic, at best. Adhesives were used to attach small die in hybrid microcircuits or to attach components to sparsely populated printed-wiring boards (PWBs). Adhesives were manually dispensed from a syringe or dabbed with a probe, and components were picked up and placed with tweezers or with a vacuum pick-up tool. With the recent proliferation of electronics in consumer products, high production attachment and curing processes have been developed along with precision automated equipment for cleaning, dispensing adhesives, placing of components, and curing of the bonded parts. New high-density devices and packaging formats have also been introduced such as chip-scale packaging, flip-chip devices, ball-grid array (BGA) packages, chip-on-board (COB), and chip stacks. Challenges have had to be met in mixing different technologies in the same assembly; examples are assembling wire-bonded die alongside flip-chip attached die, large molded inductors or capacitors along with bare-chip devices, and soldered components together with components attached and connected with electrically conductive adhesives. Indeed, in the drive to reduce costs and increase circuit densities, the trend is to use a mixture of assembly technologies.

Cost has also become a driver even for the high-end military and space electronics. This is a result of the increased use of electronics in these fields, for example, in fighter planes and spacecraft. At the same time, government budgets have been reduced. Still, high reliability is required for these systems. Thus, programs...