Expandable interposer for a microelectronic package and method therefor

A method of fabricating a microelectronic package comprising the steps of:

• providing first and second microelectronic elements having electrically conductive parts;
• providing an expandable structure disposed between said microelectronic elements;
• connecting said electrically conductive parts together so that said microelectronic elements are electrically interconnected;
• expanding said expandable structure after the connecting step so that said microelectronic elements move away from one another, wherein said microelectronic elements remain electrically interconnected during the expanding step, wherein the expanding step includes the step of heating said thermoplastic material and said foaming agent so that said thermoplastic film foams and expands.

A method of fabricating a microelectronic package comprising the steps of:

• providing first and second microelectronic elements having electrically conductive parts;
• providing an expandable structure disposed between said microelectronic elements;
• connecting said electrically conductive parts together through conductive wires so that said microelectronic elements are electrically interconnected;
• and
• expanding said expandable structure after the connecting step so that said microelectronic elements move away from one another, wherein said microelectronic elements remain electrically interconnected through said conductive wires during the expanding step, and wherein said expandable structure is more rigid during the connecting step and less rigid after the expanding step.

A method of fabricating a microelectronic package comprising the steps of:

• providing an expandable structure having a first volume;
• juxtaposing said expandable structure having a first volume between first and second microelectronic elements having electrically conductive parts and assembling said expandable structure with said first and second microelectronic elements;
• electrically interconnecting the conductive parts of said first and second microelectronic elements;
• and
• after the electrically interconnecting step, expanding said expandable structure to a second volume greater than the first volume thereof so that said first and second microelectronic elements move away from one another, wherein said first and second microelectronic elements remain electrically interconnected during the expanding step, and wherein said expandable structure is more rigid during the connecting step and less rigid after the expanding step.

A method of fabricating a microelectronic package comprising:

• providing first and second microelectronic elements having electrically conductive parts;
• disposing an expandable structure between said first and second microelectronic elements, wherein said expandable structure includes an unactivated foaming agent;
• connecting said electrically conductive parts together so that said microelectronic elements are electrically interconnected;
• and
• after the connecting step, activating said foaming agent for expanding said expandable structure so that said microelectronic elements move away from one another, wherein said microelectronic elements remain electrically interconnected during the activating and expanding steps, and wherein the expanding step includes the step of heating said thermoplastic material and said foaming agent so that said thermoplastic film foams and expands.