Key Takeaways
- Borofloat 33 glass wafers are CNC-machined to custom diameters up to 450 mm and thicknesses from 0.2 mm.
- Polished surfaces achieve a 20/10 scratch-dig quality, with total thickness variation typically below 5 µm.
- Post-processing options include edge profiling, through-holes, notches, and a range of thin-film coatings (AR, ITO, FTO).
- All custom wafers are inspected interferometrically and supplied with certificates of conformance and full material traceability.
- Lead times typically range from 4–6 weeks for custom batches; exact timing depends on quantity and complexity.
Why Material and Coating Selection Defines Substrate Performance
A cleanroom technician lifts a cassette of freshly machined Borofloat glass wafers from a CNC grinding station. Each 200mm disc must meet a flatness spec of <1µm, surface roughness below 0.5nm Ra, and edge quality that avoids particulate generation in a lithography tool. The wrong glass composition — or a missing anti-reflective coating — could shift transmission values just enough to spoil an entire batch of sensor arrays. That is why, from the first material inquiry, engineering teams prioritize substrate material and coating as one integrated decision, not an afterthought.
Glass Material Families at a Glance
Precision glass wafers are fabricated from a spectrum of material families, each with distinct characteristics. Below are the most commonly specified options for custom machined substrates.
- Fused Silica: Ultra-low thermal expansion and excellent UV transmission. Ideal for high-power laser optics and semiconductor masks.
- Borosilicate (e.g., Borofloat®, MEMpax®): A balanced choice with moderate thermal shock resistance, good chemical durability, and visible-to-NIR transmission. Borofloat 33 is widely used in anodic bonding and MEMS production.
- Soda-Lime: The most economical flat glass. Suitable for low-cost displays and microfluidic covers where thermal demands are minimal.
- Aluminosilicate: High mechanical strength and scratch resistance via ion-exchange. Often chosen for cover glasses in harsh environments or touch interfaces.
- Sapphire: Single-crystal aluminium oxide with extreme hardness (9 Mohs) and broad transmission from UV to mid-IR. Used in abrasive environments and high-pressure windows.
- Optical Glass (e.g., BK7): High homogeneity and controlled refractive index for imaging and laser components, but generally lower thermal resistance than fused silica or borosilicate.
Property Trade-offs: What to Prioritize
No single glass outperforms across all criteria. Here are the key trade-offs buyers weigh.
Optical Transmission: Fused silica leads in UV (down to 180nm), while Borofloat transmits well from ~350nm to 2µm. Sapphire extends into the mid-IR. Optical glass can be tuned for specific wavelengths but may have absorption bands.
Coefficient of Thermal Expansion (CTE): For anodic bonding to silicon, borosilicate’s CTE (~3.25 ppm/K for Borofloat 33) closely matches silicon, reducing stress. Fused silica is near zero (0.55 ppm/K), and soda-lime is much higher (~9 ppm/K), limiting its use in thermal cycling.
Thermal & Chemical Resistance: Borosilicate withstands rapid temperature changes and most acids. Fused silica handles even higher temperatures but is more expensive. Aluminosilicate offers good thermal stability after strengthening, while soda-lime risks fracture under thermal shock.
Hardness & Durability: Sapphire is the hardest, adding significant cost. Aluminosilicate can be chemically strengthened to high surface compression. Borofloat offers sufficient scratch resistance for many handling operations; cost-wise, it sits between soda-lime and fused silica.
Cost: Soda-lime is cheapest; borosilicate adds moderate premium; fused silica and optical glasses are higher; sapphire is the most expensive. Volume and post-processing also drive final part cost.
Surface Coatings and Treatments
Beyond the base material, surface modifications extend functionality or protect the wafer.
- Anti-Reflective (AR) Coatings: Applied to reduce reflection losses at specific wavelengths or broadband. AR-coated Borofloat is common for sensor windows.
- Mirror Coatings: Metallic (aluminum, gold) or dielectric coatings for high reflectivity in optics. Dielectric mirrors offer lower absorption.
- ITO (Indium Tin Oxide): Transparent conductive coating for EMI shielding, heating elements, or touch interfaces. Slight transmission loss is a trade-off.
- Hydrophobic/Oleophobic Coatings: Repel moisture and oils; used in medical devices or outdoor optics. Durability varies with abrasion.
- Tempering (Thermal Strengthening): Creates compressive surface stress for improved mechanical strength. Applicable to soda-lime and aluminosilicate; less common on Borofloat due to lower achievable stress.
- Chemical Strengthening: Ion-exchange for aluminosilicate or soda-lime to achieve high surface compression. Provides superior scratch resistance without optical distortion.
Each treatment adds lead time and cost; AR and ITO also require vacuum deposition chambers, so lot sizes matter.
How to Align Material and Coating with Your Application
Start with the primary stressor: Is it temperature, pressure, chemical exposure, or optical precision? For a semiconductor wafer handler, Borofloat with an optional AR coating often satisfies flatness and cleanliness requirements while matching silicon CTE. For a high-power UV lamp window, fused silica with a broadband AR coating transmits the required energy without degrading. In a medical imaging device, sapphire’s hardness and inertness protect sensitive optics.
Compliance is typically mandatory: all materials are supplied RoHS-compliant and REACH-conformant unless otherwise specified. Confirm with your supplier that the specific glass type and any coating formulations meet the latest directives for your target markets.
Request a Material Recommendation
Material selection rarely starts from a blank slate. Share your substrate dimensions, environmental requirements, optical goals, and target volumes with our engineering team. We will provide a side-by-side comparison of suitable glass types and coating alternatives, including application-specific trade-offs, to help you lock in the specification early.
Custom Machining Capabilities for Borofloat Glass Wafers
Borofloat 33 wafers can be CNC-machined, ground, lapped, and polished to precise customer specifications. Whether a prototype run or volume production, the process starts from raw Schott Borofloat 33 sheet, cut to near-net shape, then brought to final diameter, thickness, and surface finish through successive grinding and polishing stages.
Dimensional Control and Tolerances
Custom diameters up to 450 mm and thicknesses down to 0.2 mm are achievable. Typical dimensional tolerances are held within ±0.05 mm, with tighter tolerances available on request. Total thickness variation (TTV) below 5 µm is standard for polished wafers, ensuring flatness for lithography and bonding processes.
Surface Finishing Options
Surfaces can be supplied as-lapped, single-side polished, or double-side polished to a 20/10 scratch-dig or better. A fine-polished surface yields a mirror finish suitable for optical coatings, including broadband anti-reflection (AR) layers or indium tin oxide (ITO) conductive films. Post-polishing, wafers can receive hydrophobic or oleophobic treatments if required.
Edge Profiling and Features
Edges are typically ground with a safety bevel to prevent chipping. Other edge profiles—bullnose, pencil-grind, or flat—are available. Through-holes, notches, and wafer flats can be incorporated via ultrasonic drilling or CNC milling, making the wafers ready for automated handling systems.
Key Facts: Custom Borofloat Wafer Machining
- Material: Schott Borofloat 33 borosilicate glass (other glasses such as fused silica, soda-lime, and alkali-free aluminosilicates available).
- Diameter range: custom from 10 mm to 450 mm.
- Thickness range: 0.2 mm to 13 mm (thicker on request).
- Surface finishes: lapped, single- or double-side polished to 20/10 scratch-dig.
- Typical TTV: < 5 µm for polished wafers.
- Compliance: RoHS, REACH as standard; ISO 9001 quality management.
- Lead time: depends on quantity and complexity—typical 4–6 weeks for custom batches.
Quality and Process Control
Every custom Borofloat wafer undergoes in-process and final inspection. Flatness is verified with interferometric tools, surface quality with white-light profilometry, and dimensional accuracy with coordinate measuring machines. Certificates of conformance are provided, and full material traceability is maintained for each batch.
Packaging and Shipping
Wafers are cleaned and dried in a Class 100 cleanroom before being packed in single-slot wafer shippers or stacked in certified wafer cassettes with interleaved films. Bulk packaging is vacuum-sealed to prevent contamination during transit. For international orders, export documentation is handled in-house.
For projects requiring Borofloat 33 glass wafers or a 4-inch Borofloat 33 Glass Wafers standard product, contact our sales team. To begin a custom wafer program, send your drawing or specification for a technical review and quotation.
| Aspect | Details |
|---|---|
| Base Material | Schott Borofloat 33 (borosilicate); other glasses available: fused silica, soda-lime, aluminosilicate, sapphire |
| Diameter | Custom up to 450 mm |
| Thickness | 0.2–13 mm (thicker on request) |
| Surface Finish | Lapped, single-/double-side polished (20/10 scratch-dig) |
| Coatings | AR, ITO, FTO, mirror, hydrophobic |
| Edge Profiles | Safety bevel, bullnose, pencil-grind, flat |
| Quality Certifications | RoHS, REACH, ISO 9001 |
Frequently Asked Questions
What is Borofloat glass?
Borofloat is a floated borosilicate glass produced by Schott. It offers high thermal shock resistance, excellent chemical durability, and high transmission in the visible and near-infrared spectrum — making it a common substrate choice for semiconductor, MEMS, and optical applications.
What is the difference between Borofloat and borosilicate?
Borofloat is a specific brand of borosilicate glass manufactured by Schott using a float process. While all Borofloat is borosilicate, not all borosilicate glass is Borofloat. Borofloat 33 has a particularly low coefficient of thermal expansion and flat fire-polished surfaces, whereas generic borosilicate may vary in composition and quality.
Can Borofloat glass wafers be coated with ITO or AR layers?
Yes, Borofloat 33 wafers accept a wide range of thin-film coatings. Indium tin oxide (ITO) creates a transparent conductive layer for electrodes, while anti-reflective (AR) coatings minimize reflection losses across specific wavelength bands. Both are applied after final polishing.
What tolerances are achievable on custom Borofloat wafers?
Standard dimensional tolerances are ±0.05 mm, with tighter values achievable. Total thickness variation (TTV) can be held to less than 5 µm on polished wafers, and surface quality is specified up to 20/10 scratch-dig. Edge bevels and custom features are machined to within ±0.1 mm typically.
What is the typical lead time for custom Borofloat wafer orders?
Lead times vary with order size and complexity, but a typical range is 4–6 weeks for custom batches. Rush services may be available for small quantities; contact the manufacturer with your specifications for a precise timeline.