Ultrasonically bonding a flexible electronic circuit element having a plurality of vias

A method for bonding flexible electronic circuits to each other, comprising:

• providing a first flexible electronic circuit, wherein the first flexible electronic circuit comprises:
• a first non-conductive substrate;
• and
• a first conductive trace layer disposed on a surface of the first non-conductive substrate, the first conductive trace layer including a first bonding pad;
• providing a second flexible electronic circuit, wherein the second flexible electronic circuit comprises:
• a second non-conductive substrate having a first surface and a second surface opposite the first surface and including a plurality of vias extending from the first surface to the second surface;
• a second conductive trace layer disposed on the first surface of the second non-conductive substrate, the second conductive trace layer including a second bonding pad;
• a conductive interface layer disposed on the second surface of the second non-conductive substrate;
• and
• a plurality of conductive fillers respectively disposed within and completely filling the plurality of vias to establish a mechanical, electrical, and thermal coupling between the conductive interface layer and the second bonding pad;
• placing the first bonding pad in direct contact with the second bonding pad;
• and
• applying sufficient ultrasonic energy to the conductive interface layer to bond the first bonding pad to the second bonding pad by:
• bringing an ultrasonic horn into contact with the conductive interface layer;
• activating the ultrasonic horn;
• and
• deactivating the ultrasonic horn after the first bonding pad has become ultrasonically bonded to the second bonding pad.