Recessed Conductive Pillar for 3D IC Alignment
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Solution Overview
Problem
In three-dimensional integrated circuits, misalignment issues between conductive contacts on opposing surfaces lead to shorts and delamination problems due to material differences and thermal expansion stresses, limiting the density and reliability of stacked die configurations.
Innovation Solution
The use of conductive pillars with recesses on one substrate and filled with conductive material, allowing for precise alignment and reduced stress through the formation of inter-metallic compounds, enhancing the reliability and throughput of interconnects between substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If direct contact is made between conductive bumps and posts on opposing surfaces, then high wiring density is achieved, but misalignment occurs leading to shorts and device damage
Solution Approach 1:
The recess is formed in the conductive pillar before the bonding process, pre-positioning the contact interface to accommodate alignment variations. This preliminary structural preparation allows the pillar to self-align with the contact pad on the opposing substrate, preventing misalignment-induced shorts while maintaining high wiring density.
Solution Approach 2:
The recess acts as a cushioning feature that absorbs alignment mismatches between opposing conductive elements. By providing a recessed contact area, the design compensates for potential misalignment before contact is made, preventing harmful effects such as shorts and device damage while preserving high wiring density.
2Quantity of substance
If conductive bumps are used for direct contact, then high wiring density is achieved, but stress causes joint cracking and delamination
Solution Approach 1:
The recess creates a localized region with different mechanical properties compared to the bulk conductive pillar. This local structural modification allows the recessed area to accommodate thermal expansion differences and stress concentrations, preventing crack propagation and delamination while maintaining the overall high wiring density of the bump structure.
Solution Approach 2:
The conductive pillar structure combines different material regions - the bulk conductive material and the recessed contact region - to create a composite structure that simultaneously achieves high wiring density and improved joint stability. The recessed area can be filled with or exposed as a different material better suited for thermal and mechanical compatibility.
Data Source
AI summary
A bump structure that may be used to interconnect one substrate to another substrate is provided. A recessed conductive pillar is formed on a first substrate such that the recessed conductive pillar has a recess formed therein. The recess may be filled with a solder material. A conductive pillar on a second substrate may be formed having a contact surface with a width less than or equal to a width of the recess. The first substrate may be attached to the second substrate such that the conductive pillar on the second substrate is positioned over or in the recess of the first substrate. The substrates may each be an integrated circuit die, an interposer, a printed circuit board, a high-density interconnect, or the like.