Specialty Glass : Products & Services

SD-2: Silicon to Glass Bonding Wafers

HOYA's SD-2 substrate is designed with a coefficient of thermal expansion curve which closely matches Si single crystal.

Thermal Expansion Properties

Borosilicate glass has been widely used as a bonding material to Silicon Wafer. CTE curves of Borosilicate glass and Silicon Single Crystal Wafer cross at about 240°C. When anodic bonding is performed at 400°C, the difference of the expansions at high temperature creates residual stress in the Si chip during cooling to room temperature. As precision of LSI circuit patterning moves to less than 0.25 microns, distortion between the silicon and glass wafers becomes a critical issue.

HOYA's SD-2 substrate is engineered to minimize the distortion or bowing effect caused by the thermal mis-match between the two wafers.

Anodic Bonding

Silicon and glass wafers are generally put together by way of Anodic Bonding. This bonding is formed when positive (+) DC voltage is applied to the Si wafer and negative (-) is applied to the glass wafer while the wafers are pressed and heated. During the bonding process, a small amount of Na+ ions, engineered into SD-2, move as electroconductive carriers to facilitate a very short bonding time.


  • Matching CTE to Si Wafer
  • No Phase Separation
  • Optimized for Anodic Bonding
  • Reduced Fresnel Diffraction
  • High Flatness Mask
  • High Young's Modulus


  • Silicon Wafer Bonding
  • Photolithography
  • Pressure Sensors
  • Displacement Sensors
  • Semi Conductor
Thermal Properties
SD-2 Borosilicate
Coefficient of Thermal Expansion 32.0x10-7/°C 32.5x10-7/°C
Transformation Point (Tg) 721°C 552°C
Sag Point (Ts) 787°C  
Strain Point 669°C 510°C
Annealing Point 720°C 560°C
Thermal Conductivity 0.0026 Cal/sec•cm•°C 0.0027 Cal/sec•cm•°C
Specific Heat 0.176 Cal/g•°C 0.180 Cal/g•°C
Mechanical Properties
Specific Gravity 2.60 2.23
Young's Modulus 8860 kgf/mm2 6400 kgf/mm2
Modulus of Rigidity 3560 kgf/mm2  
Poisson's Ratio 0.244 0.200
Knoop Hardness 638 kgf/mm2 418 kgf/mm2
Electrical Properties
Volume Resisitivity (DC500V) 20°C 4.1 x 1014 Ω•cm 1.4 x 1016 Ω•cm
Volume Resisitivity (DC500V) 100°C 4.2 x 1011 Ω•cm 4.6 x 1011 Ω•cm
Volume Resisitivity (DC500V) 200°C 3.8 x 109 Ω•cm 0.9 x 109 Ω•cm
Dielectric Coefficient (1MHz) 20°C 6.0 4.8
Dielectric Coefficient (1MHz) 100°C 7.0 4.9
Dielectric Coefficient (1MHz) 200°C 7.0 5.1
Dielectric Loss (1MHz) 20°C 1.0 x 10-2 5.5 x 10-3
Dielectric Loss (1MHz) 100°C 1.9 x 10-2 1.0 x 10-2
Dielectric Loss (1MHz) 200°C 4.9 x 10-2 2.9 x 10-2
Chemical Properties
Acid Durability
(30% HNO3 80°C 50H)
1.20 mg/cm2 loss 0.50 mg/cm2 loss
Alkaline Durability
(0.01N NaOH 50°C 15H)
0.01 mg/cm2 loss 0.02 mg/cm2 loss
Optical Properties
Refractive Index (nd) 1.531 1.474
Abbe-Number (vd) 59  

Note: The listed data are standard value. Because of continuous product improvement, the various data listed are subject to change without notice.