Substrate-Less Flip-Chip Die Stack Assembly With Suspended Bottom Die
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Solution Overview
Problem
Current flip-chip techniques require flip-chip die stacks to be attached to a carrier base, limiting the ability to create substrate-less assemblies that reduce signal paths between active elements in microelectronic components.
Innovation Solution
A fabrication tool with air cavities below die openings allows for the assembly of a substrate-less flip-chip die stack by suspending the bottom die's interconnect bumps in air, enabling bonding of the top die's interconnect bumps to the bottom die's landing pads without attaching the bottom die to a substrate, using a reflow process in a fabrication tool designed to maintain the bottom die's interconnect bumps in a suspended state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flip-chip die stack is attached to a carrier base, then the die stack is supported and stable during assembly, but the signal path between active elements is lengthened
Solution Approach 1:
The invention extracts and removes the carrier base from the traditional flip-chip assembly process. By using a fabrication tool with air cavities to suspend the bottom die during assembly, the carrier base is completely eliminated, achieving substrate-less flip-chip die stacks that reduce signal path length while maintaining assembly stability through the tool's structural support.
2Ease of manufacture
If a carrier base is used, then the assembly process is well-established and reliable, but the integration flexibility into next-level assemblies is reduced
Solution Approach 1:
The invention changes the physical state and support parameters of the bottom die by suspending it in air cavities during assembly rather than attaching it to a solid carrier base. This parameter change enables the bottom die's interconnect bumps to remain unbonded and available for subsequent integration into next-level assemblies, significantly improving adaptability while using a controlled fabrication process.
Solution Approach 2:
The fabrication tool provides dynamic support during the assembly process, allowing the bottom die to be held in a suspended state temporarily. This dynamic approach enables flexibility for subsequent integration steps while maintaining stability during the critical assembly phase, resolving the contradiction between process reliability and integration versatility.
3Strength
If the bottom die is attached to a substrate, then the die is firmly supported, but the interconnect bumps are bonded and cannot be used for further integration
Solution Approach 1:
The fabrication tool with air cavities acts as an intermediary support structure during assembly. It provides the necessary mechanical support and stability for the bottom die without causing the interconnect bumps to bond to a substrate. This intermediary approach allows the bumps to remain unbonded and available for subsequent integration into next-level assemblies.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the creation of a substrate-less flip-chip die stack for flexible integration into next-level assemblies, reducing signal paths and enhancing communication between components by maintaining the bottom die's interconnect bumps in an unbonded state, facilitating easier integration and potentially improving performance.
Implementation Method 1
inserting the fabrication tool containing the stacked die structure into a reflow oven and reflowing the stacked die structure
Data Source
AI summary
One aspect of the present disclosure pertains to a method of assembling a flip-chip die stack. The method includes picking a bottom die where the bottom die incudes first interconnect bumps. The method includes placing the bottom die into an opening of a fabrication tool. The bottom die has an exposed portion hovering over an air cavity below the opening. The method includes picking a top die where the top die includes second interconnect bumps. The method includes placing the top die onto the bottom die to form a stacked die structure, inserting the fabrication tool containing the stacked die structure into a reflow oven, and reflowing the stacked die structure. After reflowing the stacked die structure, the second interconnect bumps are bonded to landing pads of the bottom die, and the first interconnect bumps remain unbonded.