The close attached capacitor: a solution to switching noise problems

The authors present an analysis of a novel low-cost, post-attach bypassing technique called close attached capacitor (CAC), which offers an attractive alternative to managing switching noise in single or multichip packages. The CAC is a thin flat capacitor, comparable in size to an IC die, that is placed on the active surface of the die and connected to onchip power and ground pads through very short bonds. By locating the CAC on the face of the die, the inductance of chip bonds and associated outer lead bond pads is avoided and less interconnect area is needed. Some environmental testing of the CAC process has been performed, indicating no device parameter degradation when attachment is made to the active surface of a passivated die. CAC design issues are addressed, and the feasibility of manufacturing high-frequency capacitors and their assemblies using conventional reworkable or permanent attach processes is demonstrated. Examples of the integration of CACs in high-performance single chip packages and to chips on multichip modules are shown, and the effectiveness of CACs in the reduction of switching noise is demonstrated