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AF 32® eco

Alkali-free alumina-borosilicate thin glass

Special Properties

  • Alkali-free in synthesis*
  • Low thermal expansion coefficient
    very close to that of silicon
  • Very smooth surfaces
  • High optical transmission
  • Good surface quality and flatness
  • Low micro roughness < 1 nm (RMS)
  • Application temperature up to approx. 600 ° C

Typical Applications

  • Alkali-free glass wafers for semiconductor applications
  • MEMS (Micro-Electro-Mechanical Systems)
  • Wafer for Mikroarrays
  • Covers for optoelectronics and optical sensors
  • Substrates for hybrid electronics
  • Electronic displays
  • Interposer
  • Glass spacers
  • Alkali-free microscopy glasses

The alumina-borosilicate glass AF 32® eco is alkali-free in synthesis*. It is made by the down-draw manufacturing process. This technology has been developed by SCHOTT and allows the production of very thin glass thicknesses. It features a low micro roughness of typ. < 1 nanometer (RMS). AF 32® eco has a coefficient of thermal expansion of 3,2 x 10-6, that is very close to the CTE of silicon. This opens up a wide range of applications in the semiconductor industry. Wafers for MEMS applications (micro-electro-mechanical systems) are often made of AF 32® eco glass. Likewise in research there are numerous applications for this high-quality thin glass. For example, we regularly manufacture alkali-free microscope slides and cover slips from AF 32® eco with various dimensions and shapes. Not least in science and research there are numerous fields of applications AF32 glass material can be used for. We manufacture alkali-free microscope slides, coverslips, glass wafer components and various optics for photonics research based on this high quality thin glass. AF 32® can be precision-cut with diamond tools on CNC-machines or it can be processed by laser-cutting. A high light transmission in the visible as well as in the infrared range up to approx. 2700 nm, allows many interesting optical and optoelectronic applications. In addition to the very good transmissivity for visible and infrared wavelengths, particularly the smaller thicknesses offer a good optical transmission down to the UVB range. The "eco" in the glass brand name stands for the production with eco-friendly refining agents SCHOTT uses for the melting of all AF32 glass thicknesses. AF32 is currently available in the thickness range from 0,10 to 0,50 mm. (See chart)


To request a window, substrate, wafer, microscope slide, cover slip or any kind of optics made of AF 32® eco alkali-free* glass with individual dimensions, please click the button below:


Request for Quotation

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*Caused by low alkali traces in the raw materials and resulting from the production process according to SCHOTT an alkali content of 0,2 weight per cent of the glass might be possible.



Light Transmission of SCHOTT AF 32® eco glass

Click to enlarge light transmission curve of SCHOTT AF 32® eco glass

Display transmission spectrum of AF 32® eco


Optical Properties

  • Abbe number: ve= 62,4

AF 32 eco glass, Index of Refraction


Wavelength (nm)

Refractive Index


Mechanical Properties

  • Density: 2,43 g/cm3
  • Young's modulus E: 74,8 kN/mm2
  • Stress optical coefficient C:
    3,1 x (1,02 x 10-12 m2/N)
  • Poisson's ratio μ: 0,238
  • Torsion modulus G: 30,2 kN/mm2
  • Knoop hardness HK0,1/20: 490
  • Vickers hardness HV0,2/25: 540

Thermal Properties

  • Coefficient of thermal expansion :
    3,2 x 10-6/K (20 °C ; 300 °C)
  • Viscosities:
    • Softening Point (107,6 dPa): 970 °C
    • Annealing Point (1013 dPa): 731 °C
    • Strain Point (1014,5 dPa): 686 °C
  • Transformation temperature Tg: 717 °C

Chemical Properties

  • Hydrolytic resistance according to DIN ISO 719:
    • Resistance class HGB 1
    • Equivalent of Alkali (Na2O) per g of glass grains: 10 μg/g
  • Acid resistance according to DIN 12 116:
    • Resistance class 4
    • Half surface weight loss after 6 h:
      >60 mg/dm2
  • Alkali resistance according to DIN ISO 695:
    • Resistance class A3
    • Surface weight loss after 3 h:
      210 mg/dm

Electrical Properties

  • Dielectric constant εr:
    • 5,1 (1 MHz)
    • 5,1 (1 GHz)
    • 5,1 (5 GHz)
  • Dielectric loss factor(tan δ at 25 °C):
    • 28 x 10-4 (1 MHz)
    • 35 x 10-4 (1 GHz)
    • 49 x 10-4 (5 GHz)
  • Electric volume resistivity ρD:
    • 7,9 x 1011 Ω x cm (250 °C)
    • 1,1 x 1010 Ω x cm (350 °C)
    • 1,5 x 108 Ω x cm (500 °C)

Available AF 32® eco thicknesses

(Click on a glass thickness to request it)

Glass thickness


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0,100 ±0,015
0,200 ±0,020
0,300 ±0,020
0,400 ±0,020
0,500 ±0,030


All given details and specifications are mean reference values and are not guaranteed. In addition, please consider our "Notes on technical specifications"