Several surface mounted package types are currently in use, including plastic leaded chip carriers (PLCC), plastic quad flat packs, small outline packages and ball grid array (BGA) packages. Each package type supports an IC chip, or "die", and provides interconnections between the die and a printed circuit board (PCB).
FIG. 1 shows an example of a typical molded IC package 10. A lead frame 20 is the central supporting structure of the molded IC package 10 to which all other elements are attached. The lead frame 20 is etched or stamped from a thin metal strip to form a pattern of narrow leads 22 radially arranged around a central die attach platform 24 upon which a die 30 is mounted via an epoxy resin 40. The die 30 has a lower surface 32 contacting the epoxy resin 40 and an opposing upper surface 34 facing away from the die attach platform 24, and includes die bond pads 36 located on the upper surface 34. The die bond pads 36 are electrically connected to the leads 22 of the lead frame 20 by fine-diameter gold wires 50 using well established wire bond techniques. The lead frame 20, die 30 and wires 50 are covered with a thermoset plastic casing 60 using an operation called transfer molding. As indicated in FIG. 1, the plastic casing 60 includes an upper portion 62 formed over and contacting the upper surface 34 of the die 30, and a lower portion 64 formed under and contacting a lower surface 25 of the die attach platform 24. After transfer molding, leads 22 of lead frame 20 are plated, trimmed and formed to complete the molded IC package 10.
A problem with conventional molded IC package 10 is that, because the plastic casing 60 completely surrounds the die 30, heat dissipation from the tie 30 is resisted. More specifically, the heat generated by the die 30 during normal operation must pass through the upper portion 62 of the plastic casing 60, and through the epoxy resin 40, die attach portion 24 and lower portion 64 of the plastic casing 60. Due to the insulating properties of the plastic casing 60, this heat dissipation is resisted, thereby creating, in some instances, high temperatures within the package 10 which can impair or damage the die 30.
A second problem is the physical size (thickness) of the conventional molded IC package 10. Specifically, the epoxy resin 40, die attach platform 24 and lower portion 62 of the plastic casing 60 substantially increase the overall thickness of the conventional molded IC package 10.
A third problem associated with the conventional molded IC package 10 is that the assembly process is complicated by the steps of applying the epoxy resin 40 onto the die attach platform 24, and then placing the die 30 onto the epoxy resin 40.