Ultrasonic vibration-assisted scribing of sapphire - effects of ultrasonic vibration and tool geometry
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2025-01-23 |
| Journal | The International Journal of Advanced Manufacturing Technology |
| Authors | Shah Rumman Ansary, Sarower Kabir, Cynthia Nnokwe, Rui He, Weilong Cong |
| Citations | 3 |
| Analysis | Full AI Review Included |
Technical Documentation & Analysis: UV-A Scribing of Sapphire
Section titled âTechnical Documentation & Analysis: UV-A Scribing of SapphireâSource Paper: Ultrasonic vibration-assisted scribing of sapphire: effects of ultrasonic vibration and tool geometry (The International Journal of Advanced Manufacturing Technology, 2025)
Executive Summary
Section titled âExecutive SummaryâThis research validates the critical role of diamond material properties and precise tool geometry in achieving superior surface integrity during the machining of ultra-hard, brittle materials like sapphire using Ultrasonic Vibration-Assisted (UV-A) scribing.
- Performance Enhancement: UV-A scribing significantly reduced vertical cutting force by up to 50% compared to conventional scribing, particularly at lower feeding depths (< 6 ”m).
- Ductile Regime Extension: The critical feeding depth for the ductile-to-brittle transition was successfully extended from 6 ”m (conventional) to approximately 10 ”m using optimized UV-A parameters.
- Optimal Tool Geometry: A sharp 60° single-diamond cutting tool proved optimal, reducing cutting force by 65% and generating the lowest average edge chipping and residual stress.
- Residual Stress Mitigation: UV-A scribing effectively lowered compressive residual stress within the scribed grooves, enhancing the structural integrity of the sapphire workpiece.
- Material Removal Mechanism: Optimized UV-A parameters (40-60% ultrasonic power) promoted a more ductile material removal regime, minimizing microcrack propagation and brittle fracture.
- Application Relevance: These findings are directly applicable to optimizing diamond tooling for high-precision wafer separation (Scribing and Breaking, SnB) in semiconductor and optoelectronic manufacturing.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard data points were extracted from the experimental setup and results, highlighting key operational parameters and performance metrics.
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Workpiece Material | C-plane Sapphire | N/A | Single-side polished wafer |
| Workpiece Hardness (Vickers) | 2300 | N/A | Ultra-hard material characteristic |
| Workpiece Thickness | 650 | ”m | Wafer dimension |
| Feed Rate (Vf) | 10 | mm/s | Constant experimental parameter |
| Ultrasonic Frequency (f) | 20 | kHz | Constant experimental parameter |
| Ultrasonic Power Levels Tested | 0, 20, 40, 60, 80 | % | Variable input for UV-A system |
| Max Vertical Ultrasonic Amplitude (A) | 4.4 | ”m | Achieved at 80% ultrasonic power |
| Tool Tip Angles (Ξ) | 60, 90, 120 | degree | Variable single-diamond tool geometry |
| Max Cutting Force Reduction (UV-A) | 50 | % | Achieved at feeding depths < 6 ”m |
| Max Cutting Force Reduction (60° Tool) | 65 | % | Compared to other tool geometries |
| Critical Feeding Depth (Conventional) | 6 | ”m | Ductile-to-brittle transition point (0% power) |
| Critical Feeding Depth (UV-A Enhanced) | ~10 | ”m | Enhanced ductile regime limit (40% power) |
| Optimal Ultrasonic Power Range | 40-60 | % | Yielded minimum average cutting force and edge chipping |
| Stress-Free Raman Peak | 417 | cm-1 | Nondegenerate lattice vibration mode |
| Max Raman Peak Shift (0% power) | > 422 | cm-1 | Indicating maximum compressive residual stress |
Key Methodologies
Section titled âKey MethodologiesâThe experimental investigation utilized a Rotary Ultrasonic Machining (RUM) system and advanced metrology to quantify the effects of UV-A scribing parameters.
- Workpiece Preparation: C-plane sapphire wafers (100 mm diameter, 650 ”m thickness) were cut into 70 mm x 20 mm workpieces and secured to a dynamometer.
- Tooling: Single-diamond cutting tools with conical tips and three specific angles (60°, 90°, and 120°) were employed.
- UV-A System Setup: A RUM system provided high-frequency (20 kHz) mechanical vibrations to the cutting tool via a piezoelectric transducer and horn.
- Parameter Variation: Experiments were conducted across five ultrasonic power levels (0%, 20%, 40%, 60%, and 80%) for each of the three tool geometries.
- Feeding Depth Control: The workpiece was tilted at a 0.06° angle to ensure a gradual, controlled increase in feeding depth (d) along the scribe length, allowing for analysis up to 10 ”m.
- Force Measurement: Vertical cutting forces were captured using a quartz-piezoelectric dynamometer (Kistler Type 9272) and filtered to obtain mean cutting force values.
- Surface Metrology: An Optical Microscope (OM) was used to observe scribe features and measure edge chipping width, quantified using ImageJ software.
- Residual Stress Analysis: Raman spectroscopy was performed on the scribed grooves to analyze residual stress by measuring the shift of the 417 cm-1 Raman peak, following ASTM standards D7027-20 and G171-24.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThis research underscores the critical need for high-quality, geometrically precise diamond tooling to maximize the benefits of advanced machining techniques like UV-A scribing. 6CCVD is uniquely positioned to supply the necessary MPCVD diamond materials and custom fabrication services required to replicate and advance this research in industrial settings, particularly for semiconductor wafer processing.
| Research Requirement | 6CCVD Solution & Capability | Technical Advantage |
|---|---|---|
| High-Precision Scribing Tool Material (Single-diamond tool, low wear) | Optical Grade Single Crystal Diamond (SCD) | SCD offers the highest purity, hardness (Mohs 10), and thermal stability, ensuring the 60° tool tip geometry remains sharp and consistent, minimizing tool wear and maximizing the ductile removal regime. |
| Custom Tool Geometry & Angles (60°, 90°, 120° tip angles) | Custom Laser Cutting and Shaping Services | 6CCVD fabricates SCD and PCD plates and wafers, offering precise laser cutting and shaping to achieve exact tool tip angles and dimensions required for specialized UV-A machining heads. |
| Large-Scale Wafer Processing (100 mm diameter sapphire wafers) | Polycrystalline Diamond (PCD) Plates up to 125 mm | For industrial Scribing and Breaking (SnB) applications, 6CCVD provides large-area PCD wafers up to 125 mm, suitable for high-throughput semiconductor manufacturing. |
| Ultra-Low Surface Roughness (Minimizing edge chipping, Ra < 5 nm) | Advanced Polishing (Ra < 1 nm for SCD, < 5 nm for PCD) | Our internal polishing capability ensures the diamond tools possess an ultra-smooth finish, which is essential for reducing friction, lowering cutting force, and inhibiting microcrack propagation during UV-A scribing. |
| Integration into RUM Systems (Custom substrate thickness) | SCD and PCD Substrates up to 10 mm Thickness | We supply diamond materials in custom thicknesses (0.1 ”m to 500 ”m SCD/PCD layers, up to 10 mm substrates) ready for mounting and integration into complex ultrasonic spindle subsystems. |
| Metalization for Bonding/Mounting (Tool attachment) | Internal Metalization Services (Au, Pt, Ti, W, Cu) | 6CCVD offers custom metalization layers, ensuring reliable, high-strength bonding of the diamond tool to the ultrasonic horn or spindle, critical for transmitting high-frequency vibrations effectively. |
Engineering Support
Section titled âEngineering SupportâThe successful extension of the ductile-to-brittle transition depth from 6 ”m to 10 ”m through optimized UV-A parameters is a significant achievement. 6CCVDâs in-house PhD team specializes in the material science of diamond machining and can assist engineers and scientists in selecting the optimal SCD grade and tool geometry to maximize ductile mode cutting and minimize residual stress for similar wafer separation and micro-machining projects.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
Abstract In recent years, semiconductors, electronics, optics, and various other industries have seen a significant surge in the use of sapphire materials, driven by their exceptional mechanical and chemical properties. The machining of sapphire surfaces plays a crucial role in all these applications. However, due to sapphiresâ exceptionally high hardness (Mohs hardness of 9, Vickers hardness of 2300) and brittleness, machining them often presents challenges such as microcracking and chipping of the workpiece, as well as significant tool wear, making sapphires difficult to cut. To enhance the machining efficiency and machined surface integrity, ultrasonic vibration-assisted (UV-A) machining of sapphire has already been studied, showing improved performance with lower cutting force, better surface finish, and extended tool life. Scribing tests using a single-diamond tool not only are an effective method to understand the material removal mechanism and deformation characteristics during such UV-A machining processes but also can be used as a potential process for separating IC chips from wafers. This paper presents a comprehensive study of the UV-A scribing process, aiming to develop an understanding of sapphireâs material removal mechanism under varying ultrasonic power levels and cutting tool geometries. In this experimental investigation, the effect of five different levels of ultrasonic power and three different cutting tool tip angles at various feeding depths on the scribe-induced features of the sapphire surface has been presented with a quantitative and qualitative comparison. The findings indicate that at feeding depths less than 6 ÎŒm, UV-A scribing with 40-80% ultrasonic power can reduce cutting force up to 50% and thus improve scribe quality. However, between feeding depths of 6 to 10 ÎŒm, this advantage of using ultrasonic vibration gradually diminishes. Additionally, UV-A scribing with a smaller tool tip angle (60°) was found to lower cutting force by 65% and improve scribe quality, effectively inhibiting residual stress formation and microcrack propagation. Furthermore, UV-A scribing also facilitated higher critical feeding depths at around 10 ÎŒm, compared to 6 ÎŒm in conventional scribing.
Tech Support
Section titled âTech SupportâOriginal Source
Section titled âOriginal SourceâReferences
Section titled âReferencesâ- 2009 - Sapphire [Crossref]