Spacer-Controlled Solder Bonding for CTE-Mismatched Optical Assemblies
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Solution Overview
Problem
Optical devices with mismatched coefficients of thermal expansion (CTEs) face thermal stress and alignment issues due to thin solder bond lines, which can crack under temperature cycling and result in misalignment as the solder bond line thickness increases.
Innovation Solution
Incorporating a precisely controlled spacer within the solder bond line to maintain a consistent thickness and prevent solder creep, thereby reducing the likelihood of cracking and misalignment while allowing for increased solder bond line thickness to mitigate thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the solder bond line thickness is increased to mitigate thermal stress, then the reliability under thermal cycling improves, but the alignment precision deteriorates due to solder creep
Solution Approach 1:
A spacer is introduced as an intermediary element between the first component and second component. The spacer has a controlled coefficient of thermal expansion and serves as a mechanical stop that maintains a predetermined distance between components. This allows the solder to wet the spacer and component surfaces while preventing excessive solder flow and creep, thereby maintaining alignment precision even with thicker solder bonds that provide thermal stress resistance.
Solution Approach 2:
The patent changes the physical parameters of the bonding system by introducing a spacer with specific material properties (controlled CTE, predetermined thickness). This allows optimization of the solder bond line thickness independently of the alignment constraint, as the spacer physically limits the maximum solder thickness and prevents creep while allowing sufficient thickness for thermal stress mitigation.
2Manufacturing precision
If the solder bond line is made thin to maintain alignment precision, then the alignment precision is maintained, but the solder bond line cracks under thermal stress
Solution Approach 1:
The spacer acts as a mediator that enables the solder bond line to be sufficiently thick for crack resistance while preventing it from being too thick to cause alignment issues. The spacer provides a physical barrier that controls solder flow and prevents creep, allowing the solder to achieve optimal thickness for thermal stress resistance without sacrificing alignment precision.
3Manufacturing precision
If a thin solder bond line is used, then the alignment precision is maintained, but the solder creeps and causes misalignment
Solution Approach 1:
The spacer serves as a stable intermediary that prevents solder creep. By providing a physical stop and controlling the bond line thickness, the spacer eliminates the space available for solder to creep into, thereby maintaining alignment stability over time and under thermal cycling conditions while preserving initial alignment precision.
4Reliability
If the spacer material has CTE matched to one component, then thermal stress on that interface is reduced, but thermal stress increases at the other interface
Solution Approach 1:
The patent optimizes the spacer material's coefficient of thermal expansion to fall within a specific range (0.1-10 ppm/°C) rather than matching exactly to either component. This parameter optimization balances the thermal stress distribution across both interfaces, preventing excessive stress concentration at either the first or second interface while maintaining overall reliability.
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
The solution effectively controls solder bond line thickness, reducing the risk of cracking and misalignment, enhancing the reliability and performance of optical devices by maintaining precise component alignment and thermal stability.
Implementation Method 1
The one or more opto-mechanical components may be attached to the base structure, in a desired position and alignment, using a layer of solder.
Implementation Method 2
an optical device includes a base with a first coefficient of thermal expansion (CTE); and an opto-mechanical component with a second CTE attached to a surface of the base via a solder layer, wherein the first CTE and the second CTE differ by greater than a threshold amount
Data Source
AI summary
In some implementations, an optical device may include a base with a first coefficient of thermal expansion (CTE). The optical device may include an opto-mechanical component with a second CTE attached to a surface of the base via a solder layer. The first CTE and the second CTE may differ by greater than a threshold amount. A spacer may be disposed within the solder layer to attach the opto-mechanical component to the base.