Silicon Watch Component Surface Smoothing via Isotropic Etching
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Solution Overview
Problem
Silicon watch components are fragile due to limited plastic deformation range and surface roughness from deep reactive ion etching, leading to mechanical weakness and potential breakage under stress.
Innovation Solution
A method involving an isotropic mechanical reinforcement treatment using an etching fluid through a protective coating, selectively smoothing etched surfaces without affecting protected areas, and optionally followed by thermal oxidation to enhance mechanical strength and reduce surface defects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If deep reactive ion etching is used to manufacture silicon watch components, then micrometric precision and simultaneous manufacture of multiple parts are achieved, but surface roughness with flatness defects and ripples is created which weakens mechanical strength
Solution Approach 1:
The patent applies a preliminary mechanical reinforcement treatment by isotropic etching fluid to the etched surface before final assembly. This treatment smooths the wrinkled sides and removes surface defects that would otherwise weaken the component, thereby strengthening the silicon part while maintaining the manufacturing precision benefits of DRIE etching
Solution Approach 2:
The patent changes the surface parameters by applying an isotropic etching treatment that modifies the surface topology. The etching fluid selectively removes material from high-stress regions and sharp corners, rounding them off to eliminate stress concentration points while maintaining overall dimensional accuracy
2Strength
If thermal oxidation is applied to remove surface defects, then mechanical strength is improved, but dimensions of the part are significantly modified
Solution Approach 1:
The patent uses chemical etching parameters instead of thermal oxidation parameters. The isotropic etching fluid is applied under controlled conditions (temperature, concentration, time) to achieve surface smoothing with minimal dimensional change, unlike thermal oxidation which causes significant dimension modification
3Strength
If annealing treatment is applied to reduce surface roughness, then edge rounding occurs which modifies the part geometry
Solution Approach 1:
The patent applies chemical etching at lower temperatures (ambient to moderate temperatures) rather than high-temperature annealing. This changes the physical state and reaction mechanism, allowing surface smoothing through chemical dissolution rather than thermal diffusion, thereby avoiding excessive edge rounding while still improving mechanical strength
4Manufacturing precision
If silicon watch components are manufactured with sharp corners and convex edges, then manufacturing precision is maintained, but crack initiation occurs under mechanical stress leading to breakage
Solution Approach 1:
The patent converts the harmful sharp corners and convex edges into beneficial rounded features through isotropic etching. The etching fluid preferentially attacks high-curvature regions, transforming stress concentration points into stress-distributing rounded geometries, thereby converting a geometric feature that causes breakage into one that enhances 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 method improves the mechanical strength and tribological properties of silicon watch components by reducing surface roughness and defects, while maintaining the integrity of protected surfaces and avoiding edge rounding, thus enhancing their durability and performance.
Implementation Method 1
The mechanical reinforcement treatment step of the part by an etching fluid is of the isotropic type
Implementation Method 2
A first approach, described in the document EP2277822, consists in forming a layer of silicon oxide by thermal oxidation of the silicon at a temperature comprised between 900°C and 1200°C
Implementation Method 3
A second approach, described in the document CH703445, consists in applying to the silicon part (that is to say to the blank of the watch component) resulting from the etching an annealing treatment at a temperature of the order of 1000°C in reducing atmosphere
Data Source
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AI summary
The manufacturing process produces a part (10) from a micromachinable material. This part (10) constitutes a blank of the watch component and has at least one surface exhibiting an initial roughness. The process includes a step of mechanically strengthening the part with an etching fluid designed to reduce the roughness of said surface. For example, a substrate of said micromachinable material is prepared, the substrate is at least partially coated with a protective coating that leaves at least one opening, the substrate is etched through the opening in the protective coating to obtain an etched surface, the mechanical strengthening treatment is applied to said etched surface through the opening in the protective coating, and then the protective coating is removed. The etching fluid may be a plasma or a chemical etching liquid.