Electrolytic method for the etch back of encapsulated copper-Invar-copper core structures

Disclosed is a method of fabricating a microelectronic package having least one layer formed of a copper-Invar-copper core encapsulated between a pair of dielectric films. The method includes exposing a copper-Invar-copper surface of the copper-Invar-copper core, for example, exposing an edge of the copper-Invar-copper core or drilling a whole through the layer to expose internal copper-Invar-copper. The copper-Invar-copper is then shaped, that is, back etched. This is an electrolytic process where the package is immersed in a substantially pH neutral electrolyte including a counter- electrode. A preferred electrolyte is an aqueous alkali metal nitrate solution. The electrolyte wets the exposed surface of said copper-Invar-copper core. The exposed surface of the copper-Invar-copper core is rendered anodic with respect to the counter-electrode and an electrical potential is applied therebetween. This results in electrochemically etching and shaping the copper-Invar-copper surface.