AGC’s glass ceramic package substrates for semiconductor lasers and technologies
AGC’s ceramics packaging substrates
AGC developed a glass ceramics hybrid package called GCHP™ as a new glass-ceramic hybrid package substrate for high-power LED chips by using low-temperature co-fired ceramics (LTCC) technology, and launched it on the market in 2010. In an LED chip with lower power consumption, resin package substrates have shown sufficient durability. However, as the output increases, the resin deteriorates more and more. For that reason, ceramic materials have begun attracting attention. GCHP™ has come to be used in a wider range of areas in recent years, with the increase in the use of high-power LDs and SMDs.
Product overview and features
GCHP™ is a glass-ceramic composite that consists of glass frit (glass fine powder) and a ceramic filler. Having unique characteristics both as glass and as ceramic, GCHP™ is a result of the know-how AGC has accumulated over many years and it offers a variety of features that other ceramic substrates do not have.
- High heat releasing for high-power applications
- High reflectivity in a wide range of wavelengths
- High reliability ensured by glass composition
- Downsizing as a result of the formation of three-dimensional circuit
High heat releasing for high-power applications
Heat releasing is a very important factor for high-power LDs to prevent laser beams from becoming unstable when they heat up. LTCC substrates themselves generally have low heat conductivity, but GCHP™ can have an Ag (silver) block in it, and the Ag block has high heat conductivity. That is the advantage of GCHP™ substrates. This heat sink structure gives a high heat releasing performance.
When making substrates using Al2O3 (alumina), a commonly used substrate material, they must be fired at a high temperature. So, it is impossible to use conductor materials having high thermal conductivity, such as Cu (copper) and Ag (silver), and this makes it impossible to achieve high heat releasing. GCHP™ uses Ag and can effectively release heat.
High reflectivity in a wide range of wavelengths
Light has the property of reflecting off at interfaces of materials with different refractive indices. Because GCHP™ is a hybrid material of glass and ceramics, reflection is repeated at interfaces between glass and ceramics, and that is why it has high reflection characteristics. We have developed a glass composition that can incorporate a large amount of ceramic filler while maintaining the glass network structure, and this has made it possible to manufacture highly reflective package substrates.
The level of reflectivity a substrate must have depends on the design of the optical sensing device. AGC provides both white and black GCHP™ substrates: the former has high reflectivity, while the latter has low reflectivity.
High reliability ensured by glass composition
|Since GCHP™ contains glass components, it has a low Young's modulus. In such a substrate, stress is dispersed without being concentrated on a part. This characteristic is not found in ceramic substrates, and is effective in preventing cracks not only in the substrate but also in the peripheral parts of the mounted substrate.|
|LiDAR systems are expected to be used outdoors and must have UV resistance. GCHP™, a composite of glass and ceramics, hardly deteriorates when exposed to ultraviolet irradiation.|
|There is a stringent test called the sulfur resistance test to check the durability of package substrates. Package substrates must pass the test when they are assumed to be used for outdoor or automotive applications. GCHP™ does not deteriorate even under a sulfur-containing environment.|
Downsizing as a result of the formation of three-dimensional circuit
GCHP™ substrates are fabricated in accordance with the LTCC process. A metal pattern, such as Ag, is formed on an unfired substrate called a green sheet, and the substrate is fired after being multilayered. This process make it possible to form inner layer wiring and produce a three-dimensional circuit. As a result, it becomes possible to downsize the package size and to flexibly design package substrates including surface-mounted ones.
Performance, specifications and sizes of package substrates for semiconductor lasers
The features of GCHP™ are compared to those of other ceramic materials. Since Ag functions as a heat sink, GCHP™ has high heat releasing performance.
By making use of the characteristics of glass and ceramics as the materials used, it has high reliability.
Furthermore, GCHP™ allows more complicated inner layer wiring, which contributes to flexible and high-density designs.
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