What is Ceramic PCB
2018-11-23 17:52Writer: qyadminReading:
As chip components and SMT (surface mount technology) are massively accepted by electronics industry, traditional PCBs (printed circuit boards) with organic laminates as substrate material are developing towards high precision, high density and high reliability. As a relatively new type of circuit boards, Ceramic PCBs have received tremendous attention from the industry since they have been regarded as an effective solution for miniaturization achievement of modern electronic products and electronic assembly technology. Thus, this article will provide a comprehensive introduction of ceramic PCBs in terms of their characteristics, categories, fabrication method and applications.
• For Implementation of Miniaturized Electronic Products
Up to now, human society is moving towards an information society and available information and data that are ready to be processed so electronic devices is urgent to be miniaturized such as telecommunication devices, computers and automatic control equipment. In the past 10 years, miniaturization was achieved primarily by the application of semiconductor chip micro-fabrication technology. Up to now, both LSI (large-scale integration) and VLSI (very large-scale integration) have been making constant progress towards high integration, large scale and high speed and the application of micro-fabrication technology is still an initial solution for electronics miniaturization. After all, when it comes to electronic devices or systems, apart from multiple LSI and passive components, circuit functions won't be implemented unless tracing is carried out for connection. Therefore, how to assemble the maximum number of components on the surface of minimum circuit board is another concern for electronics assembly. Current relationship between market demands, components and PCB can be summarized in the following figure.
• Challenge Confronted by Traditional PCB
Fabricated in substractive process, traditional PCBs with organic laminates like epoxy, polystyrene and polytetrafluoroethylene as substrate material have been applied to participate in circuit assembly as early as latter half of 1950s. Even on the day when VLSI is widely applied, they are still applied to large extent. However, with the advent of SMT and constantly improving of semiconductor circuit integration, traditional PCBs have to face up with the following challenges when they are used in high-reliability electronic products.
a. Heat Dissipation Challenge
Along with increasingly wider application of VLSI and SMT development trend, organic laminated based PCBs are quite challenged by heat dissipation in terms of design, which results from low thermal conductivity of most ordinary PCBs. Nevertheless, ceramic features thermal conductivity that is 90 times of that of epoxy glass fiber, leading to excellent conduction cooling. Moreover, components on ceramic PCBs usually feature a lower junction temperature (Tj) than that on ordinary PCBs.
b. CTE Compatibility Challenge
SMT that became popular in the early half phase of 1980s is affecting the whole electronic assembly industry. Since SMT makes electronic components directly soldered onto both sides of PCB, compared with THT (through hole technology), SMT leads to lower cost and higher reliability. Furthermore, it makes it more accessible to implement automation and capable of reducing circuit size by five sixths.
Some reliable packages, LCC (leadless chip carrier) for example, are so compatible with SMT requirement but they usually fail to withstand challenges brought by thermal cycle. As a result, LCC is doubted from the perspective of packaging reliability to interconnection on board, which is because CTE (coefficient of thermal expansion) incompatibility between LCC and PCB material leads to soldering failure. Therefore, ceramic PCBs come into being. Ceramic PCBs are capable of providing optimal solutions for defeating thermal cycle failure because they share compatible CTE with leadless ceramic chip carrier and feature higher thermal conductivity, higher stability and inertia.
Properties of Ceramic PCB
Compared with traditional PCBs whose substrate materials are epoxy glass fiber, polyimide, polystyrene and phenolic resin, ceramic PCBs feature the following properties:
• Excellent thermal conductivity
• Chemical erosion resistant
• Agreeable mechanical intensity
• Compatible with CTE of components
• Easy to implement high-density tracing.
Due to increasingly multiple functions, miniaturization and high speed of electronic devices and upsizing of IC, more rigorous requirement has to be set to ceramic PCBs in terms of CTE, thermal conductivity, loss, dielectric constant and tape resistance. It can be estimated that ceramic PCBs will be increasingly more called for with aluminum nitride, mullite and glass ceramic as substrate material.