Borofloat 33 Glass Wafers
SCHOTT Borofloat 33 borosilicate glass wafers — CTE-matched to silicon for anodic bonding, with high chemical durability and > 90% transmission from 310nm to 2,700nm for MEMS, microfluidics, and optical applications.
Overview
Borofloat 33 is a borosilicate float glass developed by SCHOTT with a low coefficient of thermal expansion (3.25 × 10⁻⁶/K from 20–300°C) that closely matches silicon. This CTE match, combined with high chemical durability and optical transparency, makes it the material of choice for anodic bonding, microfluidic devices, and through-glass via (TGV) interposers.
We supply Borofloat 33 wafers from 100mm to 300mm diameter in thicknesses from 200μm to 1,100μm, with fire-polished, SSP, DSP, or CMP surface finishes. Every wafer is individually measured and packaged in a Class 100 cleanroom environment.
Borofloat 33 is anodic-bonding ready — its CTE (3.25 × 10⁻⁶/K) matches silicon closely enough for reliable, void-free bonds to Si wafers at 300–450°C.
Borofloat 33 vs. Silicon
For MEMS and microfluidics, Borofloat 33 offers a unique combination that bulk silicon cannot: optical transparency, electrical isolation, and CTE matching to silicon for low-stress wafer bonding.
Borofloat 33 Glass
CTE-matched to silicon
CTE 3.25 ppm/K, optically transparent, electrically insulating, hydrolytic Class 1. Ideal for anodic bonding, microfluidics, and optical MEMS where silicon is opaque or conductive.
Silicon (Si)
Active-device standard
CTE 2.6 ppm/K, opaque in the visible range, electrically conductive, higher cost. Preferred for active electronic devices and high-temperature processing beyond 500°C.
MEMS & Microfluidics
Borofloat 33 supports the three core fabrication steps of glass-based MEMS: isotropic HF etching for microchannels, anodic bonding to silicon capping wafers, and through-glass via formation for 3D interconnects.
Microfluidic Channels
Isotropic HF etching produces smooth, rounded microchannels with well-controlled depth. Borofloat's optical clarity enables direct optical inspection and fluorescence detection through the substrate.
Anodic Bonding
CTE-matched to silicon, Borofloat 33 anodically bonds to Si wafers at 300–450°C with bond strengths exceeding 10 MPa, forming hermetic, void-free seals without intermediate adhesive layers.
Through-Glass Vias
Laser-assisted and plasma-etched via holes are metallized to form high-density vertical interconnects with aspect ratios up to 10:1, enabling 2.5D/3D glass interposers for RF and high-bandwidth applications.
Anodic Bonding Process
Anodic bonding (also called field-assisted or electrostatic bonding) joins Borofloat 33 glass to silicon without adhesives. At 300–450°C with 400–1,000V applied across the stack, oxygen ions migrate toward the silicon interface, forming a permanent Si–O covalent bond.
The result is a strong (> 10 MPa), hermetic, and chemically inert bond. The glass-to-silicon interface is fully transparent to optical inspection, and the bond withstands subsequent dicing, grinding, and wet processing steps.
GINECHIP's anodic bonding service covers substrate cleaning, alignment, and bonding on production equipment with uniform field distribution, supporting wafer sizes from 100mm to 200mm with yield rates optimized for volume manufacturing.
Bio-MEMS & Life Sciences
Borofloat 33 is a preferred substrate for lab-on-chip diagnostics, DNA arrays, and cell-culture devices. Its hydrolytic Class 1 chemical resistance per ISO 719 prevents ionic leaching that could alter pH-sensitive assays, while its transparency enables real-time optical and fluorescence readout.
For cell-based assays, Borofloat's low surface roughness (RMS < 1.0nm) and particle-controlled packaging minimize non-specific binding and background noise, delivering reproducible results across production batches.
Specifications
| Parameter | Available Range / Values |
|---|---|
| Material | Borofloat 33 (SCHOTT), equivalent borosilicate float glass |
| Diameter | 100mm (4″), 150mm (6″), 200mm (8″), 300mm (12″) |
| Thickness | 200μm–1,100μm, standard SEMI thicknesses |
| CTE (20–300°C) | 3.25 × 10⁻⁶/K |
| Strain Point | 525°C |
| Softening Point | 825°C |
| Density | 2.20 g/cm³ |
| Refractive Index | n₅₈₉ = 1.4714 |
| Dielectric Constant | 4.6 at 1 MHz |
| Surface Roughness (AFM RMS) | < 1.0nm standard |
| TTV | ≤ 5μm |
| Bow / Warp | Bow ≤ 25μm |
| Transmission Range | > 90% from 310nm to 2,700nm |
| Chemical Resistance | Hydrolytic Class 1, Acid Class 1, Alkali Class 2 (per ISO 719 / DIN 12116) |
| Surface Finish | SSP (Single-Side Polish) or DSP (Double-Side Polish), fire-polished or CMP |
| Packaging | Interleaved cleanroom paper, single-wafer cassette, vacuum-sealed |
Typical Applications
Microfluidics
Isotropic HF etching forms smooth microchannels; optical clarity enables fluorescence detection through the substrate.
Anodic Bonding
CTE-matched to silicon, bonds hermetically to Si wafers at 300–450°C with strengths above 10 MPa.
Through-Glass Vias (TGV)
Metallized via holes create high-density vertical interconnects with aspect ratios up to 10:1 for 2.5D/3D glass interposers.
Electrochemical Devices
Dielectric constant 4.6 at 1 MHz and high purity support electrochemical sensors and micro-electrode arrays.
Biochips & Lab-on-Chip
Hydrolytic Class 1 resistance prevents ionic leaching; transparency enables real-time optical readout for diagnostics.
Capacitive MEMS
Low dielectric loss and high dimensional stability improve capacitive pressure sensors and accelerometers.
Metrology & Quality Control
Every Borofloat 33 wafer is individually inspected. A full metrology report — including CTE verification, surface roughness, transmission, flatness, and chemical resistance data — accompanies each shipment.
Request a Borofloat 33 Quote
Send your custom specifications to our engineering team for a fast quote. We’ll review your requirements and get back promptly.