Grid Array Interconnect

The density of IC packaging technologies such as ball grid array (BGA) and chip scale packages continues to increase. In turn, this requires greater intercoimection density in the printed circuits onto which they are assembled. The need for increased density in the PCB impacts each of the components of the base material as well as the way in which they are manufactured. To achieve high levels of interconnection, component pitch densities result in smaller and more closely spaced plated through holes and circuit features. As the space between these holes and features decreases, the potential for conductive anodic filament (CAE) failures increases substantially. 

This chapter focuses on the design variables that impact the reliability of PWB-to-package interconnect (second- and third-level interconnect) of grid array devices and the impact of lead-free conversion on these design variables. 

Substrates made by the multilayer process from tape cast alumina have received considerable attention in recent years for multichip module (MCM) applications. An MCM consists of an array of closely packed chips on an interconnect board several inches on a side. Cofired ceramic is attractive relative to organic laminates because its thermal conductivity is almost 2 orders of magnitude higher, an important consideration in high-density circuitry. In addition both alumina and aluminum nitride ceramics are more closely matched to silicon in CTE than are organic boards. For similar reasons, alumina and AIN are attractive for ball grid array (EGA) mounting of chips. ... 

In actual applications, solder interconnects are often under complex loading conditions (Ref 25). For example, ball grid array (EGA) solder joints may be simultaneously under cyclic shear loading and static tensile (or compressive) loading often with vibration. The deformation behavior and reliability prediction under complex loading conditions warrant further examination. Time and path-dependent creep models are needed for the solder joints under different and often complex loading conditions (Ref 2). 

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