Thermal management issues and evaluation of a novel, flexible substrate, 3-dimensional (3-D) packaging concept

The 3D MCM is an attractive choice to meet the speed, power, weight and cost-effectiveness requirements of current electronic packaging, but presents challenges in terms of thermal management, reliable high density electrical interconnects, and mechanical configuration. This paper addresses the thermal and electrical aspects of flexible substrate (flex) 3D MCM structures. A 3D polymer-based flex substrate configuration is proposed, and modeling results show the concept´s feasibility. Test results are presented and discussed relative to modeling results. The flex configuration is discussed in terms of the high density electrical interconnection using elastomers and SMT connections between flex layers. Although flex has low thermal conductivity, tests and simulation show that up to 6 W can be dissipated through a 6 mm×6 mm area. Vias contribute to an increased interconnect density and assist with thermal management. Moreover, epoxy used to attach die to flex and flex to heat spreader should be used sparingly to reduce thermal resistance. Better thermal and electrical performance can be realized by a flip chip configuration rather than wire bonded chips, as a flipped die is best cooled from the upper side. Consideration must be given to assembly process and operational stresses, and the implications of such factors on system performance are discussed. Furthermore, the impact of the use of embedded passives on interconnect and passive device densities in terms of electrical performance is addressed. Finally, the future direction of the work is reviewed