Cruciform Bonding Pads for Alignment-Tolerant 3D-IC Interconnects
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Solution Overview
Problem
In 3D packaging, variations in alignment between substrates lead to inconsistent bonding areas, affecting the reliability and density of electrical connections in applications like CMOS image sensors and SoC devices, where traditional bonding methods fail to maintain consistent contact area and high yield.
Innovation Solution
The use of oblong and angled bonding pad surfaces, which are aligned crosswise, reduces variations in bonding area due to alignment shifts, maintaining a consistent contact area while allowing for efficient area utilization and high-density bonding, with the bonding pads being rectangular or elliptical in shape to optimize alignment and contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional bonding methods are used with square or circular bonding pads, then the bonding process is simple, but alignment variations cause inconsistent bonding areas and low yield
Solution Approach 1:
The patent applies asymmetry by using rectangular bonding pads with specific aspect ratios (e.g., 2:1 or 3:1) instead of symmetric square or circular pads. The pads are oriented at angles (e.g., 45 degrees) relative to the alignment direction, creating an asymmetric configuration that compensates for alignment variations. This asymmetric design ensures that the bonding area remains relatively constant even when alignment shifts occur, thereby improving bonding consistency and yield.
Solution Approach 2:
The patent changes the geometric parameters of the bonding pads, specifically the aspect ratio and orientation angle. By optimizing these parameters (e.g., using aspect ratios of 2:1 or 3:1 and angles of 45 degrees), the design compensates for alignment variations. This parameter optimization ensures that the bonding area remains stable despite misalignment, improving both reliability and productivity.
2Manufacturing precision
If alignment tolerance is reduced to improve bonding precision, then bonding area consistency improves, but manufacturing complexity and cost increase
Solution Approach 1:
The asymmetric rectangular pad design with specific orientations (e.g., 45 degrees) reduces sensitivity to alignment variations. This geometric asymmetry allows the bonding process to tolerate larger alignment tolerances while maintaining consistent bonding areas, thereby improving manufacturing precision without increasing alignment control complexity.
Solution Approach 2:
By optimizing the aspect ratio and orientation angle of the bonding pads, the design achieves robustness against alignment variations. This parameter optimization allows for relaxed alignment tolerances while maintaining bonding precision, reducing the complexity of alignment control systems and processes.
3Reliability
If bonding pad area is increased to compensate for alignment variations, then bonding consistency improves, but area utilization efficiency decreases
Solution Approach 1:
The asymmetric rectangular pad design with optimized aspect ratios (e.g., 2:1 or 3:1) and specific orientations (e.g., 45 degrees) achieves bonding consistency without requiring excessive pad area. The asymmetric geometry ensures that the bonding area remains stable despite alignment variations, while the optimized dimensions maintain efficient substrate area utilization.
Solution Approach 2:
By optimizing the aspect ratio and orientation angle of the bonding pads, the design achieves a balance between bonding consistency and area utilization. The optimized parameters ensure that the pads are large enough to maintain consistent bonding areas despite alignment variations, but not so large as to waste substrate area, thereby improving both reliability and area efficiency.
4Productivity
If high-density bonding is implemented to meet device demands, then device functionality improves, but sensitivity to alignment variations increases
Solution Approach 1:
The asymmetric rectangular pad design with specific aspect ratios and orientations reduces the sensitivity of high-density bonding arrays to alignment variations. By orienting pads at angles (e.g., 45 degrees) and using optimized aspect ratios, the design ensures that even at high densities, the bonding areas remain consistent despite alignment shifts, thereby maintaining device functionality while reducing alignment sensitivity.
Solution Approach 2:
By optimizing the aspect ratio and orientation angle of bonding pads in high-density arrays, the design reduces sensitivity to alignment variations. The optimized parameters ensure that the bonding process remains robust even when pads are closely spaced, allowing high-density bonding to achieve improved device functionality without excessive alignment sensitivity.
Data Source
AI summary
A bonding structure that may be used to form 3D-IC devices is formed using first oblong bonding pads on a first substrate and second oblong bonding pads one a second substrate. The first and second oblong bonding pads are laid crosswise, and the bond is formed. Viewed in a first cross-section, the first bonding pad is wider than the second bonding pad. Viewed in a second cross-section at a right angle to the first, the second bonding pad is wider than the first bonding pad. Making the bonding pads oblong and angling them relative to one another reduces variations in bonding area due to shifts in alignment between the first substrate and the second substrate. The oblong shape in a suitable orientation may also be used to reduce capacitive coupling between one of the bonding pads and nearby wires.