Misaligned Metal Pillar Connector Structures for IC Passivation
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Solution Overview
Problem
The existing interconnect structures in integrated circuits face limitations in performance and density, and the connector structures, including bond pads and metal bumps, are prone to passivation cracking due to misalignment and thermal expansion differences between the die and package substrate.
Innovation Solution
The connector structures are designed with misaligned metal pillars and pads, where the centers of the metal pillars are shifted away from the centers of the underlying metal pads, reducing the likelihood of passivation cracking and improving robustness by increasing the overlap with the polymer layer, and accounting for thermal expansion differences through careful alignment before reflow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If metal pillars are aligned with metal pads, then electrical connection is achieved, but passivation cracking occurs due to thermal expansion differences
Solution Approach 1:
The patent introduces intentional misalignment between metal pillars and metal pads, creating an asymmetric configuration where the metal pillar center is offset from the metal pad center. This asymmetric design allows the connector structure to accommodate thermal expansion differences between the die and package substrate, preventing passivation cracking while maintaining electrical connectivity through the overlapping region.
2Object-affected harmful factors
If metal pillars are misaligned from metal pads, then passivation cracking is reduced, but alignment precision deteriorates
Solution Approach 1:
The patent applies local quality by creating different functional zones within the connector structure. The misaligned configuration provides a specific offset distance that is optimized for thermal expansion accommodation, while the overlapping region maintains sufficient electrical connection. This localized optimization allows the structure to tolerate misalignment while ensuring reliable electrical connectivity in the overlap zone.
3Ease of manufacture
If connector structures are formed with standard alignment, then manufacturing is simplified, but robustness against thermal expansion is reduced
Solution Approach 1:
The patent implements preliminary action by pre-misaligning the metal pillars relative to the metal pads during the manufacturing process, before the reflow step. This pre-established offset configuration ensures that when thermal expansion occurs during subsequent processing or operation, the connector structure is already positioned to accommodate the expansion without causing passivation cracking, thereby improving robustness while maintaining manufacturing feasibility.
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
This design enhances the robustness of the connector structures, reduces passivation cracking, and maintains alignment post-reflow by strategically misaligning metal pillars relative to metal pads, addressing the limitations of existing interconnect structures and thermal expansion issues.
Implementation Method 1
accounting for thermal expansion differences through careful alignment before reflow
Data Source
AI summary
A die includes a substrate, a metal pad over the substrate, and a passivation layer covering edge portions of the metal pad. A metal pillar is formed over the metal pad. A portion of the metal pillar overlaps a portion of the metal pad. A center of the metal pillar is misaligned with a center of the metal pad.