A Case for Multiple Sheet Resistivities for Thin Film Embedded Resistor Packaging Applications

Designers of high performance electronics continue to have system requirements that necessitate the implementation of embedded resistors in microelectronic package and multilayer printed circuit applications. The reasons most commonly given for this shift in technology are performance enabling, reduction in form factor, and relief from routing complexity. The advantages realized with embedded resistors make a strong case for implementation in both new and legacy designs. Until recently, thin film resistors with a maximum sheet resistivity of 250 ohms/square were available. This constrained the practical limit of resistor values to about 10k ohms for small form factor packages and limited resistor footprint. The advent of a robust 1000 ohm/square thin film resistor has allowed designers to expand their range of resistors values that can easily be captured and still maintain a reasonable resistor form factor. Values to 100k ohms and greater are reachable, and when 1000 ohm/square and lower ohm/square materials are used together in multilayer packages, the resistor capture capability can reach into the 90+ percentage. In this paper, an actual case, the use of multiple sheet resistivities and their practical use, will be discussed. Low ohm/square material, i.e. 10 or 25 OPS, used in combination with the 1000 OPS will be compared to a Bill of Materials with terminating and pull-up/down and the capture potential. The introduction of a 1000 ohm/square thin film embedded resistor material for this and other applications will also be covered