THE CLOSE ATTACHED CAPACITOR - A SOLUTION TO SWITCHING NOISE PROBLEMS

A potentially serious problem, which high performance systems face is switching or delta-I noise. There are many techniques for managing switching noise, the most common of which involves the use of bypass capacitors. This paper presents an analysis of a new 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 on-chip 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 are avoided, and valuable interconnect area is saved. 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. In this paper, 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 CAC's in high performance single chip packages and to chips on multichip modules (MCM's) are shown, and the effectiveness of CAC's in the reduction of switching noise is demonstrated.