Overview of Low-Temperature Sealing Glass
Sealing refers to the process in which sealing materials, when heated, bond tightly with other materials, achieving a well-wetted interface. Among many sealing materials, sealing glass is one of the most well-known and widely used. In a broad sense, sealing glass serves as an intermediate layer glass that seals materials such as glass, ceramics, metals, and composites.
Low-temperature sealing glass is the most widely used type of sealing glass. It has a low softening or melting temperature (<600°C) and offers various excellent properties, such as high heat resistance, corrosion resistance, and high insulation strength. Its composition can be adjusted to suit different bonding materials.
Performance Requirements of Low-Temperature Sealing Glass
For sealing glass to achieve reliable bonding with the substrate, it must meet the following performance and process requirements:
- Appropriate Softening Temperature: The softening temperature affects the sealing temperature. A high softening temperature may cause damage to the substrate and reduce the sealing strength.
- Matched Thermal Expansion Coefficient: The thermal expansion coefficient difference between the substrate and the glass should be within ±5%, not exceeding ±10%, to avoid stress and cracking.
- Good Chemical Stability: The glass must withstand corrosion from the environment.
- Good Wettability: Proper wettability ensures strong bonding with the substrate.
Types of Low-Temperature Sealing Glass
Low-temperature sealing glass can be categorized into crystalline and non-crystalline types. Due to the limitations of traditional glass systems in microelectronics, composite low-temperature glass systems have emerged. These include:
- Lead Glass System: Lead-based glasses are commonly used due to their low melting temperature, good insulation, and corrosion resistance. However, because of lead's toxicity, lead-free alternatives are being developed.
- Bismuth Glass System: Bismuth-based glasses are considered the best replacement for lead-based glasses, offering similar properties without the toxicity concerns.
- Phosphate Glass System: Phosphate glasses have lower melting temperatures but require additives to improve their stability and performance.
- Borate Glass System: Borate-based glasses offer high glass transition and softening temperatures but need further development for low-temperature applications.
- Vanadate Glass System: Vanadate glasses have low glass transition and softening temperatures but are costly and toxic in vapor form.
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