Through-Substrate Metal Posts for 3D Die Stacking
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Solution Overview
Problem
Conventional 3D device packaging techniques face challenges with precise alignment of copper pillars, leading to non-wetting issues and increased footprint due to the need for additional non-electrically active pillars, as well as the requirement for underfill and dam structures to manage voids between stacked dice.
Innovation Solution
The use of through-substrate pillar and stud bump bonding techniques, where metal pillars or stud bumps are inserted into corresponding holes in the substrate to form mechanical and electrical connections, reducing the risk of non-wetting and eliminating the need for underfill and dam structures by minimizing the standoff distance between dice.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper pillars are used for die stacking, then mechanical and electrical bonding is achieved, but alignment precision is difficult to maintain and non-wetting occurs
Solution Approach 1:
The patent applies preliminary action by pre-forming recesses in the substrate before inserting the copper pillars. This pre-prepared receptacle structure guides the pillars into proper alignment during insertion, eliminating the need for high-precision alignment between opposing pillars on stacked dies. The recesses act as mechanical guides that ensure correct positioning before bonding occurs.
Solution Approach 2:
The substrate recesses serve as an intermediary structure between the copper pillars of opposing dies. Rather than requiring direct pillar-to-pillar alignment, the recesses mediate the connection by providing a receiving structure that accommodates the pillars, thereby decoupling the alignment requirements from the bonding process.
2Reliability
If non-electrically active pillars are added to prevent non-wetting, then bonding reliability improves, but package footprint increases
Solution Approach 1:
The patent extracts the alignment and bonding assurance function from the copper pillars themselves and transfers it to the substrate recesses. By removing this function from the active pillars, fewer pillars are needed, eliminating the requirement for additional non-electrically active pillars and thereby reducing the package footprint while maintaining bonding reliability.
Solution Approach 2:
The copper pillars serve multiple functions simultaneously: they provide electrical connection, mechanical support, and self-alignment through their insertion into the recesses. This multi-functionality eliminates the need for separate non-electrically active pillars that would otherwise be required solely for alignment and bonding assurance.
3Productivity
If pillar-to-pillar die stacking is used, then 3D stacking is achieved, but large voids are created requiring underfill and dam structures
Solution Approach 1:
The substrate recesses are pre-formed to match the dimensions and positions of the copper pillars. This preliminary structuring allows the pillars to insert directly into the recesses with minimal standoff distance, eliminating the large voids that would otherwise form between stacked dies and removing the need for underfill and dam structures.
Solution Approach 2:
The recesses in the substrate are created as negative copies or inverse impressions of the copper pillar geometry. This copying approach ensures that the recesses perfectly accommodate the pillars, minimizing gaps and voids when the pillars are inserted, thereby simplifying the overall package structure.
Data Source
AI summary
A method for 3D device packaging utilizes through-hole metal post techniques to mechanically and electrically bond two or more dice. The first die includes a set of through-holes extending from a first surface of the first die to a second surface of the first die. The second die includes a third surface and a set of metal posts. The first die and the second die are stacked such that the third surface of the second die faces the second surface of the first die, and each metal post extends through a corresponding through-hole to a point beyond the first surface of the first die, electrically coupling the first die and the second die.