Integration of NiCr resistors in a multilayer Cu/BCB wiring system

The integration of passive components into the wiring substrate is essential for the further miniaturization and cost reduction of electronic systems. CSP and high density multilayer boards are becoming standard in the electronic industry, but a lot of space on the board must often be used for passive components. The integration of passives into the board minimizes the whole system and also reduces the assembly cost. The focus of this paper is to give an insight into the process for the integration of NiCr resistors in an MCM-D substrate. Two approaches are presented: (1) NiCr resistors directly on the substrate with the multilayer Cu/photo-BCB on top; (2) NiCr resistors between the Cu/photo-BCB layers. A test layout was designed to achieve different values of resistance. Two different technologies were used to structure the resistors. The reproducibility of the technology is described. A strong effect of the photo-BCB process on the electrical resistance of the NiCr layers was found. Thermal aging and initial reliability tests were carried out using these test structures.