In the calcium aluminosilicate CAS glass system, the thermal conductivity was increased from 1. This thermal conductivity is much higher than other LTCC systems reported [ 38 , 39 , 40 , 41 , 42 , 43 , 44 , 46 , 47 , 50 ]. The addition of AlN whiskers did not improve the thermal conductivity compared with AlN powder addition and fibrous fillers was more effective in increasing thermal conductivity of the composites.
Therefore, these two electrically conductive composites are not applicable to electrically insulating thermal management material, or they can be coated with a insulating glass layer on the surface to improve electrical resistivity [ 52 ]. Glass-free or non-glass base LTCC systems have been investigated to reduce the complexity of the LTCC systems due to the multiple phases included such as glass, filler particles, and additional sintering additives.
Due to their complexity, several problems occurred during the preparation of LTCC circuits and devices in the integrated electronic module. To overcome this complexity in chemical interaction and inhomogeneous dielectric properties and difficulties in slurry dispersion, LTCC systems with simple phase components were developed [ 54 , 55 , 56 , 57 , 58 , 59 , 60 ] Table 7.
LTCCs containing glass phase matrix generally exhibited low thermal conductivity as we have seen in Table 6. Finding a low temperature synthesis and low temperature melting crystalline phase ceramic compound is a crucial point to develop glass-free LTCCs. Glass-free LTCC compositions applicable in the industry with proven mechanical properties and reliabilities are hardly found, even though several primary research results showing excellent dielectric properties were reported [ 54 , 55 , 56 , 57 , 58 , 59 , 60 ]. The substantial problems exposed in the previous glass-free LTCC systems are weak mechanical strength, reactive with matching electrode materials during heat treatment, and vulnerable in moisture environment.
In the calcium germinates and silicates system, the dielectric constants were 6. These systems did not show any chemical reaction with Ag electrode. On the other hand, in the calcium tellurates system, the dielectric constants were The thermal conductivity of this system was not provided [ 55 ].
The microwave dielectric properties of sintered tape were measured by using split post dielectric resonator SPDR method connected with a vector network analyzer [ 56 ]. This system is compatible with silver electrode [ 58 ]. The CTE and thermal conductivity of the system were For the aforementioned glass-free system, the thermal conductivities obtained are 2.
However, the thermal conductivity was relatively low, 1. This system may be applicable to high temperature insulating dielectrics due to low CTE and high break down voltage [ 60 ]. However, regardless of excellent dielectric and thermal properties, some of the glass-free LTCC compounds containing lithium element have a water soluble problem that limits the application. Therefore, they might need a protective layer coating to resist under weathering conditions. In this chapter, recent research and development works on high thermal conductivity ceramics and their composites for thermal management of integrated electronic packages are briefly explored.
Key lessons drawn from these prior works can be summarized as follows:. Among them, silicon nitride ceramic seems the most frequently used in the power electronic applications these days. In nitrides and nitride based ceramic matrix composites, key parameters that control the thermal property are densification including pore removal, grain size and grain boundary control, impurity, and secondary phase control.
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Among them, densification is the primary factor to achieve high thermal conductivity due to high thermal resistance of pores. These nitride ceramics are difficult to sinter with high density so that spark plasma sintering and two-step sintering methods together with the addition of small amount of sintering aids should be applied to realize high densification. In nitride ceramics, controlling the oxygen content is a very important factor in addition to the parameters required in oxide materials. Some works found in the literature are mainly on re-crystallization and phase control in the matrix and show only minor improvement in thermal properties compared with the noticeable enhancement in mechanical properties.
The main reason for this minor change in thermal property in the conventional glass—ceramic type LTCC comes from the glass matrix which comprises more than half the volume of the sintered body. The volume fraction of newly evolved nano-crystalline phases through heat treatment process are so small that the overall apparent thermal conductivity might not change significantly while the mechanical strength can be easily boosted by the inclusion of the nano-crystalline phase in the matrix. Polymer matrix composites with high thermal conductivity and electrically insulating ceramic filler materials are mostly used for dielectric insulation layers in LED packaging substrate for effective heat dissipation to the metallic heat spreading panels.
Most frequently used insulating ceramic filler materials are alumina, BN, and AlN powders. Among them, BN platelet powders are preferred due to the anisotropic thermal conductivity behavior in the 2D structure of the BN crystal. Also, there are some efforts to coat ferrous or dielectric nano particles on BN platelet particles to promote the easy alignment of BN platelet particles into the intended direction.
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Polymer matrix composites with high thermal conductivity inorganic fillers such as CNT, graphite flake, and graphene nanosheets exhibited a great improvement in thermal conductivity with a little amount of additions. However, they are mostly electrically conducting so that they cannot be used for electrical circuit substrates.
Instead, these composites are mainly used for thermal interface materials.
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Ceramic materials used for applications in LED packages are typically of two types: dielectric insulating substrates for circuit forming bed and high thermal conductivity fillers for thermal interface material. Regardless of the aforementioned progresses in the development and commercialization of ceramics, there are several challenges in the high thermal conductivity ceramic based heat transfer materials:. Continuous efforts in lowering costs and cost-effective processing of high temperature sintering HTCCs with high thermal conductivity are required in materials chemistry and innovative processing techniques.
Compared to the HTCC based high thermal conductivity ceramics, LTCCs still require further enhancement in both thermal and mechanical characteristics in order to be adopted in thermal management applications. Since the major part of the conventional LTCC formulation consists of glass, the utmost thermal conductivity of the glass—ceramic filler composites thus obtained is limited and far below that of HTCC based high thermal conductivity ceramics.
Therefore, first, we need to investigate ways to improve thermal conductivity of the glass phase itself as it is done in many polymer matrix composites.
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Second, the mechanical strength of LTCC should be further improved even though some results demonstrated enhanced mechanical strength via recrystallization process through the interfacial reaction and nucleation between glass phase and crystalline filler phase. Other challenges in high thermal conductivity LTCCs may be the development of non-glass base LTCCs, which have already been attempted earlier as applications in RF and microwave dielectric materials.
The non-glass based LTCCs are exempted from the usage of low thermal conductivity glass matrix phase; they will exhibit higher thermal conductivity than the conventional type. There are many reports that state the achievement of high thermal conductivities in polymer matrix composites using high thermal conductivity ceramic fillers.
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As a practical point of view, however, simply increasing thermal conductivity of ceramic filled polymer composites does not ensure the potential use in thermal management application, especially when they are used as thermal interface materials. Other factors, such as adhesion strength to the substrates or heat sink materials for TIM application and tensile strength of thermal tapes or flexible device substrates, also should be considered in addition to thermal and electrical properties since the more filler loading, the less adhesion and tensile strength is provided.
For insulated metal substrates IMS using high thermal conductivity ceramics, a reliable solution for CTE mismatch between ceramic and metal joining inducing delamination and crack generation failure in harsh conditions such as cyclic temperature environment is still required.
In addition, for highly effective heat transfer performance IMS, we may need an ultra-thin insulation layer with high dielectric breakdown voltage together with high mechanical strength, which enables both low thermal resistance and low package profile of high power device and module. Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution 3.enter
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Downloaded: Abstract Recently, ceramic substrates have been of great interest for use in light emitting diode LED packaging materials because of their excellent heat transfer capability. Keywords thermal conductivity ceramics composites electronic packaging. Introduction Ceramic materials with high thermal conductivity are of great interest in the thermal management of integrated electronic device packaging such as high-power light emitting devices LEDs , power semiconductor modules, micro and nano fluidics, thermoelectrics, solar cells, and wireless communication devices.
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Aluminum nitride AlN base ceramics and composites 2. AlN ceramics with sintering additives Aluminum nitride AlN has a highly covalent bonded wurtzite structure with a high thermal conductivity and a low thermal expansion coefficient CTE of 4. AlN 1. Table 1. Table 2. Physical properties of AlN with carbon nanomaterials addition.
Si 3 N 4 base ceramics Silicon nitride Si 3 N 4 ceramics has been drawing a lot of interest as a high thermal conductivity dielectric material used in insulated metal substrate IMS for power electronic circuit modules. Table 3. Thermal conductivities of AlN—BN composites. Table 4. AlN-BN base composites: electrically insulating Boron nitride BN was introduced in the AlN matrix to realize low dielectric constant and moderate thermal conductivity [ 17 ]. Polymer matrix composites with high thermal conductivity ceramic fillers Polymer matrix composites for thermal management packaging are usually filled with high thermal conductivity ceramics such as AlN, h-BN, and carbon based fillers like carbon nano fibers CNTs , graphite or graphene nanosheets GNSs , and reduced graphene oxide rGO.
Polymer: BN composites In the hexagonal-boron nitride h-BN filled polymer composites, the major issues to enhance heat transfer property are surface treatment of h-BN platelet particles to improve the dispersion of the filler particles in the polymer matrix; to lower the interface thermal resistance; and to increase the alignment of h-BN particles to the preferred orientation in order to achieve high directional thermal conductivity in composites.
Table 5. Examples of thermal conductivities of polymer—BN composites. Glass-ceramic base LTCC system Recently, the use of high thermal conductivity with insulating ceramic substrate is rapidly increasing to enhance the heat transfer property of integrated electronic device and package.
The fundamental concept which will be employed in the experiment is thermal conductivity. The piece of paper wrapped around a metal cylinder should not ignite as compared to a freely held piece of paper. The black spot which will appear on the paper is not burnt paper. In fact, it is an impurity soot produced by incomplete combustion of the candle wick.
This impurity should be able to be removed via wiping or eraser. If both potential situations are compared, the piece of paper with the cylinder is in contact with the metal cylinder and air, whereas; a freely held piece of paper is only in contact with air. Due to the contact with the metal, the paper can transfer the heat of the fire to the bar. The freely held piece of paper cannot transfer the heat from the fire to only the air due to the poor thermal conductivity of the air. Therefore, the freely held piece of paper will burn. In this section put: Grab a paper cup or snow cone and fill it with water.
Place it over a candle. The cup will not burn, but the water will eventually boil.