High density interconnect embedded magnetics for integrated power

We introduce here a new transformer/inductor technology which is suitable for integrated power for multichip modules (MCM), microprocessors and chip sets. The transformer/inductor is embedded within the ceramic substrate, as are the chips and other components. It provides for extremely tight secondary side circuit layouts with very low and fixed leakage inductance. The core is a new multipole structure which can be considered as a number of transformers integrated into one monolithic structure. The core consists of a bottom ferrite plate, and the winding is constructed using high density interconnect techniques (HDI), such as laminating dielectric layers and depositing winding metals using sputtering followed by electroplating.Winding patterns are etched using photo-resist and wet etching techniques. Multiple vias are used to connect different primary and secondary winding layers. A conformal metal mask is used to laser-drill through (large) holes for the posts of the top part of the core. An experimental 50-W, six-pole transformer has been built using these techniques. It operates at 1.0 MHz with efficiency approaching 98.7% and has a net height of about 0.09 in (∼ 2.3 mm). It has a power density of 71 W/cc (or 1170 W/in 3 ) and a surface power density of 17 W/cm 2 .