These products feature thermal expansion characteristics which are extremely close to that demonstrated by silicon within a wide range of temperatures. They can be firmly bonded to silicon substrates (basal plates) through anodic bonding. As such, these products are used for support glass and wafer level packages of MEMS sensors.
- Wafer level packages for MEMS substrates (basal plates)
- Pressure sensors and acceleration sensors
- MEMS elements feature very fine and fragile structures, the type of which experience movement due to static electricity. As such, wafer level packages are often used to bond and seal together glass and silicon prior to the dicing process using a bonding method called “anodic bonding.”
- • Sensors featuring structures such as this detect, with a high degree of sensitivity, changes in pressure and acceleration which result from the distortion seen in the microstructures of silicon. If a difference exists in terms of the thermal expansion coefficients of the silicon and glass, the output voltage ends up fluctuating in contrast with the distortion experienced by the silicon. This may affect the precision of the sensors.
- While borosilicate glass has traditionally been used for anodic bonding, we provide a series of products called the SW Series, which further conforms with the thermal expansion characteristics of silicon single crystals. There are currently three types of glass products in the SW Series: SW-3, SW-Y and SW-YY. The SW-YY product features great thermal expansion characteristics and also allows anodic bonding to take place at temperatures which are 50 to 100 degrees (Celsius) lower than that experienced during instances where conventional borosilicate glass is used.
Table: Glass Wafer Characteristics
|Unit||SW-3||SW-Y||SW-YY||Borosilicate glass||Thermal characteristics|
|Thermal expansion coefficient||×10-7/°C||36||33||33||33||30 to 300°C|
|Strain point||℃||615||630||590||510||Japanese Industrial Standards (JIS)|
|Annealing point||℃||660||675||640||560||Japanese Industrial Standards (JIS)|
|Softening point||℃||890||895||850||820||Japanese Industrial Standards (JIS)|
|Young's modulus||GPa||80||78||82||64||Resonance method|
|Poisson's ratio||0.19||0.18||0.2||0.2||Resonance method|
|Dielectric constant||6.1||6.0||6.3||4.6||Room temperature (1 MHz)|
|Dielectric dissipation factor||0.01||0.01||0.01||0.01||Room temperature (1 MHz)|
|Acid resistance||mg/cm2||0.30||0.16||0.09||0.01||Immersion in 1/100N HNO3 at 95℃ for 20 hours|
|Alkali resistance||mg/cm2||0.09||0.17||0.16||0.14||Immersion in 5% NaOH 80℃ for 1 hour|
|80°C for 1 hour|
|Water resistance||mg/cm2||0.05||0.07||0.05||0.04||Immersion in pure water at 95℃ for 40 hours|
|Features||General product||Low-expansion product||Low expansion product, low-temperature bonding|
Thermal Expansion Characteristics (Comparison with Silicon and Other Types of Glass)
Difference in Thermal Expansion Coefficient Compared to Silicon
Metal (gold, chromium, titanium, etc.) coating on substrates (basal plates), ultrasonic machining and sand blasting, as well as hole completion performed via etching, spot facing, and other types of machining