Electrical circuit designers often face the problem of needing to implement electrical circuits using as little space as is practical. Circuit space is often a valuable asset which needs to be conserved, and the miniaturization of electrical circuits often improves speed, reduces noise, and leads to other performance advantages. The packages within which semiconductors are housed play a large role in determining the space needed for implementing an electrical circuit because larger packages require more space.
Traditionally, semiconductors have been housed in packages which consume an order of magnitude or more area than the actual semiconductor die which represents the electrical component. When an electrical circuit requires several semiconductor components, the circuit requires an amount of space dictated by the components' packages and interconnections between the packages.
"Flip chip" or direct chip attachment mounting techniques are used to increase the density of electrical circuits. Flip chip mounting techniques relate to "flipping" an integrated circuit semiconductor die over and directly attaching a single active or top surface of the die to a printed wiring board. The attachment conventionally occurs through solder bumps formed on the metalized pads or contacts of the die. Since the actual semiconductor die size is so much smaller than a typical semiconductor package, tremendous improvements in electrical circuit space requirements can result.
However, various types of semiconductors have two active surfaces rather than just one. In the case of a transistor, a collector contact usually resides on one surface of the die while emitter and base contacts reside on an opposing surface of the die. In the case of a diode, an anode contact usually resides on one surface of the die while a cathode contact resides on an opposing surface of the die. Such components cannot simply be flipped over and attached to a printed wiring board because electrical coupling will not be made between the printed wiring board and one of the active surfaces.
Moreover, when electrical circuits include both planar contact devices and non-coplanar contact devices, flip chip manufacturing processes become more complicated. Such processes must be able to attach planar contact semiconductor dice to printed wiring boards using flip chip techniques and attach semiconductor packages to the printed wiring boards using conventional semiconductor package handling techniques. These complicated manufacturing processes are more expensive and more prone to errors than would be the case were the manufacturing processes required to accommodate only flip chip attachment techniques.
USPTO Backgrounds
USPTO Backgrounds