A novel process for protecting wire bonds from sweep during molding

Wire bonding remains the lowest cost and most flexible method for interconnection of semiconductors. A major factor limiting the density of this widely used interconnect technology is wire sweep during the molding processes. Design rules for wire length, wire diameter and bond pad pitch are in many cases constrained by the need to avoid sweep, potentially compromising manufacturers´ ability to keep pace with industry roadmaps. For gold wire diameters of 25-30 μm, the wire stiffness allows the molding process some latitude. As wire diameters shrink to fit the ball bonds on the periphery of smaller or more complex devices, the molding process has difficulty avoiding wire sweep. The wire encapsulation process described in this paper reduces sweep by as much as an order of magnitude for conventional as well as alternative designs, such as 3D packaging. This paper presents a process that protects the wires in such a way that wire sweep is not a constraint so that assemblers can continue to extend the capabilities of wire bonding. Two process methods are discussed, a batch method and an integrated wirebonder dispense and cure method. The reliability performance of packages made using these processes has been assessed and is reported. The encapsulated test vehicles have achieved JEDEC 3 preconditioning with 3× reflow at 240°C, temperature cycling and other accelerated life cycle reliability tests. Success at passing JEDEC level 3 and 260° has also been achieved.