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 |
Executive Summary
Section titled âExecutive SummaryâThis study investigates the effects of ultrasonic vibration-assisted (UV-A) scribing on c-plane sapphire, focusing on optimizing machining parameters (ultrasonic power and tool geometry) to improve surface integrity and reduce cutting forces.
- Force Reduction: UV-A scribing significantly lowers vertical cutting force (up to 50% reduction) compared to conventional scribing (0% power) at low feeding depths (less than 6 ”m).
- Ductile Regime Extension: The critical feeding depth for the ductile-to-brittle transition zone is extended from approximately 4 ”m (conventional scribing) to around 10 ”m using UV-A scribing, implying superior scribe quality at greater depths.
- Optimal Tool Geometry: The 60° tool tip angle consistently generated the lowest cutting forces and minimum edge chipping, reducing force by 65% compared to the 120° tool.
- Residual Stress Mitigation: UV-A scribing effectively lowers the compressive residual stress generated within the scribed grooves compared to conventional scribing, enhancing the sapphireâs surface integrity.
- Optimal Parameters: The combination of 40% ultrasonic power and a 60° tool tip angle yielded the minimum average cutting force and lowest average edge chipping over the total scribe length.
- Mechanism Insight: The periodic hammering action of UV-A facilitates a more ductile material removal mechanism, reducing the reliance on brittle fracture observed in conventional scribing.
Technical Specifications
Section titled âTechnical Specificationsâ| Parameter | Value | Unit | Context |
|---|---|---|---|
| Workpiece Material | C-plane Sapphire | N/A | Single crystal hexagonal lattice |
| Vickers Hardness | 2300 | N/A | Workpiece mechanical property |
| Youngâs Modulus | 345 | GPa | Workpiece mechanical property |
| Feed Rate (Vf) | 10 | mm/s | Constant horizontal feeding speed |
| Ultrasonic Frequency (f) | 20 | kHz | Constant vibration frequency |
| Ultrasonic Power Range | 0, 20, 40, 60, 80 | % | Experimental variable |
| Max Vertical Amplitude (A) | 4.4 | ”m | Measured at 80% ultrasonic power |
| Tool Tip Angles (Ξ) | 60, 90, 120 | degree | Single-diamond conical tools |
| Workpiece Tilting Angle (α) | 0.06 | degree | Used to achieve gradual feeding depth |
| Max Cutting Force Reduction | 50 | % | Achieved at depths < 6 ”m using UV-A |
| Critical Ductile Depth (UV-A) | ~10 | ”m | Feeding depth before high brittle fracture dominates |
| Stress-Free Raman Peak | 417 | cm-1 | Nondegenerate lattice vibration mode (A1g) |
| Max Raman Shift (0% Power) | > 422 | cm-1 | Indicates maximum compressive residual stress |
| Optimal Scribing Combination | 40% Power, 60° Tip | N/A | Yields minimum average cutting force |
Key Methodologies
Section titled âKey Methodologiesâ- Experimental Setup: Scribing was performed on a Rotary Ultrasonic Machining (RUM) system (Series 10, Sonic-Mill), consisting of an ultrasonic spindle, a horizontal feeding subsystem (linear stage), and a data acquisition subsystem.
- Workpiece Preparation: Single-side polished c-plane sapphire wafers (100 mm diameter, 650 ”m thickness) were cut into 70 mm x 20 mm workpieces.
- Gradual Feeding Depth: Workpieces were tilted at a 0.06° angle using a 0.05-mm thick feeler gauge to ensure a gradual, continuous increase in feeding depth along the scribing length.
- Tooling: Three single-diamond conical cutting tools with tip angles of 60°, 90°, and 120° were used.
- Parameter Variation: Experiments were conducted across five ultrasonic power levels (0%, 20%, 40%, 60%, 80%) for each of the three tool geometries.
- Force Measurement: Vertical cutting forces were captured using a quartz-piezoelectric dynamometer (Kistler Type 9272) and filtered to obtain mean cutting force values at specific feeding depths.
- Scribe Feature Analysis: An Optical Microscope (OM) was used to observe and measure scribe features, including the calculation of edge chipping width at five different locations per scribe line.
- Residual Stress Quantification: Raman spectroscopy (LabRAM HR Evolution) was employed to analyze residual stress by measuring the shift of the 417 cm-1 Raman peak in the scribed grooves relative to the stress-free surface.
Commercial Applications
Section titled âCommercial ApplicationsâThe findings regarding optimized UV-A scribing of sapphire are critical for industries requiring high-precision processing of hard, brittle materials:
- Semiconductor Wafer Separation (SnB Process): The primary application is improving the Scribing and Breaking (SnB) process for separating integrated circuit (IC) chips from sapphire wafers, providing a cleaner, more efficient dry method than traditional techniques.
- Optoelectronics and LED Manufacturing: Sapphire is the dominant substrate for high-brightness LEDs. Minimizing edge chipping and residual stress via UV-A scribing is essential for maximizing device yield and functional performance.
- Ultra-Precision Machining of Ceramics: The demonstrated ability of UV-A to extend the ductile-mode cutting regime to greater depths (~10 ”m) is directly transferable to optimizing grinding and cutting processes for other hard, brittle ceramics (e.g., SiC, quartz, glass).
- High-Performance Windows: Manufacturing abrasion-resistant sapphire windows for military, aerospace, and industrial applications, where surface integrity and minimal subsurface damage are paramount.
- Biomedical Devices: Production of sapphire components for surgical instruments and wearable devices, benefiting from the reduced microcracking and improved surface quality achieved through optimized UV-A processing.
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]