Two-Stage Optical Lens Molding with Shrinkage Correction
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Solution Overview
Problem
Existing wafer-level optical lens manufacturing processes face challenges in achieving precise lens shape due to material shrinkage during curing, leading to deviations from intended design specifications, and often require iterative trial-and-error methods to compensate for shrinkage.
Innovation Solution
A method involving two or more successive molding operations using multiple masters and spacers to form a lens, where a majority of the lens volume is created with a 'blob' that shrinks, and a thin layer is added to correct deformities, ensuring the final lens meets design specifications with minimal interface effects by using materials with similar refractive indices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single molding operation is used to form the lens, then the manufacturing process is simple, but the lens shape deviates from design specifications due to shrinkage during curing
Solution Approach 1:
The lens molding process is divided into two distinct stages: a first molding operation that forms a pre-final lens shape, and a second molding operation that forms a correction layer to compensate for shrinkage. This segmentation allows each stage to serve a specific function - the first stage establishes the bulk shape while the second stage corrects dimensional deviations caused by curing shrinkage.
Solution Approach 2:
The first molding operation performs a preliminary action by forming a pre-final lens shape that intentionally includes shrinkage compensation. The mold cavity is designed to create a lens that is slightly larger than the final desired shape, so that when shrinkage occurs during curing, the lens achieves the correct final dimensions. This preliminary action anticipates and compensates for the harmful effect of shrinkage.
2Manufacturing precision
If iterative trial-and-error methods are used to compensate for shrinkage, then the lens shape precision is improved, but the manufacturing time and complexity increase
Solution Approach 1:
The shrinkage compensation is built into the first mold cavity design before manufacturing begins. By calculating and incorporating the shrinkage compensation factor into the initial mold geometry, the process eliminates the need for iterative adjustments and trial-and-error modifications during subsequent production cycles.
Solution Approach 2:
The mold cavity dimensions are specifically designed with adjusted parameters that account for the shrinkage characteristics of the lens material. The first mold cavity is sized to produce a pre-final lens that is deliberately oversized by a calculated amount, ensuring that after shrinkage during curing, the lens achieves the exact final dimensions specified in the design.
3Manufacturing precision
If a correction layer is added to the lens, then the lens shape precision is improved, but the manufacturing process complexity increases
Solution Approach 1:
The lens structure is segmented into two functional parts: the main lens body formed in the first molding operation, and a thin correction layer formed in the second operation. This segmentation allows the complex shrinkage compensation function to be isolated in a separate layer, simplifying the overall process design and making it more manageable.
Solution Approach 2:
The correction layer is applied only where needed - as a thin surface layer on the pre-final lens. This local approach concentrates the shrinkage compensation function in a specific region rather than requiring complex modifications throughout the entire lens structure, thereby reducing overall process complexity.
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 avoids the need for iterative processes, ensuring the final lens closely approximates the desired shape with reduced shrinkage errors, meeting design specifications while minimizing optical distortions and reflections.
Implementation Method 1
The pre-final lens is at least partially cured, during which it may sag or shrink.
Implementation Method 2
an aliquot of polymeric material is added to the lens and formed with the same master with a spacer, or with a second master, to form a first surface layer that provides correction between the pre-final lens shape and a final desired lens shape
Implementation Method 3
The blob and the top layer form an interface that is substantially filled with an index matching material.
Data Source
Figure 1A~1C
Figure 2A~2
Figure 3A~3B
AI summary
A lens, such as a lens for use in a wafer-level camera, is made by forming a polymeric material with at least one master to form a pre-final lens. The pre-final lens forms a majority of a final volume of the lens. The pre-final lens is allowed to harden, during which it may sag or shrink. An aliquot of polymeric material is added to the lens and formed with the same master with a spacer, or with a second master, to form a first surface layer that provides correction between the pre-final lens shape and a final desired lens shape. In an embodiment, the surface layer has similar or identical index of refraction to the pre-final lens. In an embodiment, the lens is formed on a substrate. In an embodiment, a send master, or master pair, are used to form a lens having upper and lower curvature, with a second aliquot of polymeric material forming a second surface layer on a surface of the lens opposite to the first surface layer.