Method for making an electronic circuit assembly

A method for making an electronic circuit assembly, comprising the steps of:

• (a) providing a precircuit comprising:
• (i) a metallic sheet made of a first metal and having a top surface and a bottom surface;
• (ii) a first conductor pattern attached to the bottom surface of the metallic sheet and made of a second metal, wherein the first conductor pattern comprises:
• (A) a base pad having a first predetermined size and shape and a base pad perimeter thereabout,
• (B) a circuit trace, and
• (C) first and second pedestal pads disposed proximate the circuit trace on opposite sides thereof;
• (iii) a second conductor pattern attached to the top surface of the metallic sheet and made of a third metal, wherein the second conductor pattern comprises:
• (A) a plurality of masking pads arranged generally within the base pad perimeter, wherein each masking pad has a second predetermined size and shape smaller than the base pad, and
• (B) a bridging element having first and second enlarged ends and a constricted portion therebetween, the bridging element being oriented generally transverse to the circuit trace with each enlarged end disposed opposite a respective one of the pedestal pads;
• and
• (iv) a substrate having an electrically insulative surface to which the first conductor pattern is attached;
• (b) etching the precircuit in an etchant which etches substantially only the first metal, so as to form undercuts in the metallic sheet directly beneath the masking pads;
• and
• (c) continuing to etch the precircuit and undercut the masking pads to create a circuit,
• (i) such that the metallic sheet beneath each masking pad is substantially completely undercut causing the masking pads to detach from the metallic sheet, thereby providing a plurality of bumps made of the first metal disposed atop the base pad within the base pad perimeter to form a bonding pad,
• (ii) wherein a pedestal made of the first metal is formed between each pedestal pad and its respective enlarged end of the bridging element, thereby providing an air bridge crossover above the circuit trace.