Wire bonding limitations for high density fine pitch plastic packages

The limits of process capability for fine pitch high density packages are shown. By the help of a special design test die and a PQFP (plastic quad flat package) frame, three different wire diameters with different lengths were bonded, molded, analyzed, and compared. Different ball sizes with special design capillary were made and measured. These measurements were used to study the ball size deformation before and after bonding. How a correct bonded ball should look and what size initial ball diameter must be chosen for each wire diameter and pad are also discussed. The effects of loop-height on pad pitch reduction and an improved loop structure are also examined. In addition, attention is given to what is the minimum pad size for today´s technology for different wire diameter, how a minimum pad size should be calculated, what is the minimum and maximum wire length and loop height which the existing wirebonders are capable of bonding, what are the molding limits, and what are the wire deflection limits