Cryogenic Lens Alignment Using Indium Solder Reflow
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Solution Overview
Problem
The existing method of aligning and fixing a lens assembly to a focal plane array at ambient temperatures is time-consuming and lacks sufficient accuracy due to thermal contraction and expansion issues when cooled to cryogenic temperatures, which is inadequate for precise applications.
Innovation Solution
A method involving upper and lower cold shields with cylindrical walls and indium-coated bumps and pads allows precise alignment and fixing of the lens assembly to the focal plane array at cryogenic temperatures, using a laser to re-flow the indium solder for permanent attachment, maintaining alignment accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the lens assembly and focal plane array are aligned and fixed at ambient temperature, then the alignment process can be completed, but thermal contraction during cooling to cryogenic temperatures causes misalignment
Solution Approach 1:
The patent changes the temperature parameter from ambient to cryogenic during the alignment and fixing process. By performing alignment at cryogenic temperature, the system ensures that the lens assembly and focal plane array are positioned accurately while already in their operational thermal state, eliminating subsequent misalignment from thermal contraction
Solution Approach 2:
The patent applies preliminary cooling to bring the lens assembly and focal plane array to cryogenic temperature before alignment and fixing. This preliminary thermal conditioning ensures that all components are in their final thermal state during alignment, preventing later dimensional changes
2Manufacturing precision
If the reiterative alignment process is used to achieve precise alignment, then alignment accuracy improves, but the time required increases significantly
Solution Approach 1:
The patent performs the cooling action preliminarily before alignment, bringing components to cryogenic temperature in advance. This eliminates the need for repeated heating and cooling cycles, achieving precise alignment in a single pass and dramatically reducing total alignment time
Solution Approach 2:
The patent inverts the conventional sequence by cooling components before alignment rather than aligning at ambient temperature and then cooling. This reversal of the process sequence achieves the same alignment accuracy without requiring multiple reiterative cycles
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 method significantly reduces alignment time and enhances accuracy by allowing precise alignment and fixing at cryogenic temperatures, minimizing thermal expansion-induced misalignment issues.
Implementation Method 1
The solder is melted and then solidified to permanently attach the upper and lower cold shields to each other
Implementation Method 2
The solder is melted and then solidified to permanently attach the upper and lower cold shields to each other
Implementation Method 3
The solder may be melted by applying a localized heat, such as by directing a laser beam at the solder
Implementation Method 4
as the lens assembly and focal plane array are cryogenically cooled, these parts contract according to their coefficient of thermal expansion
Data Source
AI summary
A method of aligning a lens assembly to a focal plane array is provided. The method may comprise the steps of providing an upper cold shield which holds the lens assembly, providing a lower cold shield for holding the focal plane array, mounting the upper cold shield onto the lower cold shield, lowering the temperature of the upper and lower cold shield to a cryogenic level, translating the upper cold shield with respect to the lower cold shield until the lens assembly is aligned to the focal plane array while the upper and lower cold shields are at the cryogenic temperature levels, and fixing the upper cold shield to the lower cold shield while the upper and lower cold shields are maintained at cryogenic levels.