Self-Aligned Chip Assembly for Fine-Pitch LGA Interconnects
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Solution Overview
Problem
High-density electrical interconnects, such as fine-pitch land grid array (LGA), require accurate alignment between components to ensure reliable connections, but existing methods like ball grid array (BGA) interconnects introduce mechanical and electrical performance issues due to lengthened electrical paths and impedance discontinuity.
Innovation Solution
The use of lithographically defined anisotropic etch features on photonic integrated circuits and carriers to create precise alignment features, such as pyramidal or V-groove recesses, which are engaged by cylindrical pins to achieve accurate mechanical alignment and reduce electrical loss, eliminating the need for BGA and improving alignment tolerances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ball grid array (BGA) interconnects are used, then electrical connections are established, but mechanical alignment tolerance is increased and electrical performance deteriorates due to lengthened electrical paths and impedance discontinuity
Solution Approach 1:
The patent extracts the alignment function from the electrical interconnect structure itself. Instead of relying on BGA balls to provide both electrical connection and alignment, the invention introduces separate dedicated alignment features (recesses in the substrate, protrusions on the carrier) that solely provide mechanical alignment. This separation allows the electrical interconnects to be optimized for electrical performance while alignment is handled by specialized structures.
Solution Approach 2:
The patent introduces alignment features as intermediary structures between the substrate and carrier. These alignment features (comprising recesses in the substrate and corresponding protrusions on the carrier) act as mediators that establish precise mechanical alignment before electrical connections are made, thereby improving both alignment tolerance and subsequent electrical connection accuracy.
2Reliability
If BGA interconnects are used, then electrical connections are established, but electrical performance is reduced due to lengthened electrical paths and impedance discontinuity
Solution Approach 1:
The patent extracts the alignment function from the electrical interconnect structure itself. Instead of relying on BGA balls to provide both electrical connection and alignment, the invention introduces separate dedicated alignment features (recesses in the substrate, protrusions on the carrier) that solely provide mechanical alignment. This separation allows the electrical interconnects to be optimized for electrical performance while alignment is handled by specialized structures.
Solution Approach 2:
The alignment features establish precise mechanical alignment before the electrical interconnects are engaged. The recesses and protrusions engage first to set the correct positional relationship between substrate and carrier, ensuring that subsequent electrical connections are made with optimal alignment, thereby minimizing electrical path length and impedance discontinuity.
3Manufacturing precision
If lithographically defined anisotropic etch features are used to create alignment features, then manufacturing precision is improved, but device complexity increases
Solution Approach 1:
The alignment features are created using self-aligned fabrication processes. The anisotropic etch features are formed directly in the substrate using lithographic patterns, and the corresponding protrusions on the carrier are designed to mate with these features. The self-aligned nature of the process ensures that the alignment features are automatically positioned with high precision relative to other structures on the substrate, eliminating the need for separate alignment steps and reducing overall device complexity.
Solution Approach 2:
The patent uses anisotropic etching to create three-dimensional recesses with specific geometric parameters (depth, width, angle) that provide precise mechanical alignment. By controlling etch parameters such as etch depth, etch angle, and feature dimensions, the invention achieves high alignment precision through material removal rather than adding complex alignment structures, thereby managing device complexity while improving manufacturing precision.
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 approach enhances mechanical and electrical performance by reducing mechanical alignment tolerance, lowering packaging costs, and improving electrical performance by shortening interconnect lengths and eliminating impedance discontinuities, while achieving tighter alignment tolerances and increased optical engine yield.
Implementation Method 1
The use of lithographically defined anisotropic etch features on photonic integrated circuits and carriers to create precise alignment features
Data Source
AI summary
An assembly. In some embodiments, the assembly includes a first semiconductor chip, a substrate, and a first alignment element. The alignment of the first semiconductor chip and the substrate may be determined at least in part by engagement of the first alignment element with a first recessed alignment feature, in a surface of the first semiconductor chip.