Angled Flip-Chip Bump Layout to Prevent VCSEL Cleavage Cracks
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Solution Overview
Problem
Conventional flip-chip VCSEL devices often crack along crystal cleavage planes due to mechanical strain from bondpads and bumps, leading to performance and reliability issues.
Innovation Solution
The arrangement of flip-chip bumps and gaps at a non-zero angle to the crystal cleavage plane reduces mechanical stress, minimizing the likelihood of cracking by distributing strain more evenly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flip-chip bumps are arranged aligned with the crystal cleavage plane, then manufacturing and alignment are simplified, but mechanical strain concentrates along the cleavage plane causing cracks and reduced reliability
Solution Approach 1:
The bump pattern is deliberately designed to be asymmetric with respect to the crystal cleavage plane. By orienting the bump array at a non-zero angle (e.g., 45 degrees) relative to the cleavage plane rather than parallel to it, the design breaks the symmetry that causes stress concentration, thereby preventing cracks while maintaining manufacturability through defined angular relationships.
Solution Approach 2:
The orientation angle parameter of the bump pattern is changed from 0 degrees (parallel to cleavage plane) to a non-zero angle (such as 45 degrees). This parameter modification fundamentally alters the stress distribution pattern, transforming concentrated stress along the cleavage plane into distributed stress that avoids crack initiation and propagation.
2Reliability
If gaps are oriented parallel to the crystal cleavage plane, then fabrication alignment is easier, but mechanical stress concentrates along the gap edges promoting crack formation
Solution Approach 1:
The gap structures are oriented asymmetrically relative to the crystal cleavage plane, specifically at non-zero angles. This asymmetric orientation prevents stress concentration at gap edges that would otherwise align with the cleavage plane, thereby eliminating a primary crack initiation site while maintaining sufficient alignment tolerance for manufacturing.
Solution Approach 2:
The orientation angle parameter of the gaps is changed from parallel (0 degrees) to a non-zero angle relative to the cleavage plane. This parameter change redistributes mechanical stress away from the gap edges, preventing stress concentration and subsequent crack formation, while the specific angular value maintains compatibility with standard fabrication alignment capabilities.
Data Source
AI summary
In some implementations, an optical device for mounting in a flip-chip configuration includes a plurality of flip-chip bumps that are arranged in a pattern on the optical device, wherein the pattern is not aligned with a crystal cleavage plane associated with a substrate of the optical device. In some implementations, the optical device further includes a gap that separates a primary region of the optical device and a secondary region of the optical device, wherein at least one portion of a side of the gap is oriented at a non-zero angle to the crystal cleavage plane.