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First-Level Packaging Considerations for the use of Electronic Hardware at High Temperatures
Published in F. Patrick McCluskey, Richard Grzybowski, Thomas Podlesak, High Temperature Electronics, 2018
F. Patrick McCluskey, Richard Grzybowski, Thomas Podlesak
The most common metal alloy case material is Kovar, which has a coefficient of thermal expansion closely matched to that of silicon, but has poor thermal conductivity for a metal. It is used in instances where minimizing thermal stress is more important than heat dissipation. An advantage of using Kovar is the ability to oxidize it to produce a surface suitable for glass lead sealing. Power applications use either CuW or cold-rolled steel because of their higher thermal conductivities. Cold-rolled steel is less expensive, but has a higher CTE and a lower thermal conductivity than CuW. The higher CTE creates more thermal stress in the die attach and precludes the use of matched lead seals. In addition, steel is susceptible to corrosion, as is Kovar, and is therefore often plated with gold over nickel. Stainless steel provides corrosion resistance without plating at a cost lower than copper or Kovar, but it has a thermal conductivity as low as Kovar, coupled with a high CTE. Aluminum alloys are available if package weight is a major concern, but they cannot be resistively welded and do not bond well with lead-sealing glasses.
Metals
Published in Mike Golio, RF and Microwave Semiconductor Device Handbook, 2017
Linear expansion properties of metals are important whenever metallic structures are bonded to other materials in an electronic assembly. When two materials with dissimilar thermal expansion characteristics are bonded together, significant stress is experienced during temperature excursions. This stress can result in one or both of the materials breaking or cracking and this can result in degraded electrical performance or catastrophic failure. The best choice of metals to match thermal linear expansion properties is, therefore, determined by the thermal coefficient of linear expansion of the material that is used with the metal. Kovar, for example, is often chosen as the metal material of preference for use as a carrier when alumina dielectric substrates are used to fabricate RF or microwave guided wave elements. Although Kovar is neither a superior electrical conductor nor a superior thermal conductor, its coefficient of linear expansion is a close match to that of the dielectric material, alumina. Table 12.4 presents the coefficients of linear expansion for several metals as well as other materials that are often used for RF and microwave circuits.
First-Level Packaging
Published in Mitel G. Pecht, Rakesh Agarwal, Patrick McCluskey, Terrance Dishongh, Sirus Javadpour, Rahul Mahajan, Electronic Packaging: Materials and Their Properties, 2017
Mitel G. Pecht, Rakesh Agarwal, Patrick McCluskey, Terrance Dishongh, Sirus Javadpour, Rahul Mahajan
Alloy 42 and Kovar are commonly used for lead and leadframe fabrication in ceramic chip carriers. The coefficient of thermal expansion of Kovar is 5.1 to 5.8 ppm/°C, and that of Alloy 42 is 4.0-4.7 ppm/°C, in the temperature range 20-300°C. Thus, the coefficients of thermal expansion of both these materials match well with those of silicon which are 2.3 ppm/°C, and that of ceramic substrate (3.4 to 7.4 ppm/°C). Kovar and Alloy 42 also have a high fatigue strength. Alloy 42 has a fatigue strength of 620 MPa compared with only 380-550 MPa for most copper alloys.
A review: carbon nanotubes composite to enhance thermal & electrical properties for the space applications
Published in Australian Journal of Mechanical Engineering, 2022
Dhaval A. Vartak, Yogesh Ghotekar, Pina M. Bhatt, Bharat Makwana, HN Shah, JA Vadher
The material with properties like high electrical conductivity, electromagnetic interference (EMI) shielding, electrostatic dissipation is preferable for the space applications. Traditional space materials like Aluminium, Kovar, and Invar are having high electrical conductivity and low surface resistivity. The SWCNT is the best option to improve these properties in CFRP. The electrical conductivity of composite can sharply increase by the addition of 0.3 to 0.5%wt SWCNTs. SWNT loading, indicating a percolation threshold of 0.5 wt% (Tariq, Shifa, and Baloch 2017) as shown in Figure 6. The MWCNT (1% Wt) increases the electrical conductivity of composite significantly, however, its percolation threshold is 2.5% higher than SWCNT (Ciecierska et al. 2014; Nicoletto et al. 2015) as shown in Figure 7.
Design of Heat-Resistant in-Vessel Components for Deuterium Beam-Aided Charge Exchange Recombination Spectroscopy in JT-60SA
Published in Fusion Science and Technology, 2022
A. Terakado, Y. Koide, M. Yoshida, T. Nakano, H. Homma, N. Oyama
Figure 4 shows the diagnostic window at the tip of the port plug. The diagnostic window consists of one cover glass, one cover glass frame, one vacuum flange with sapphire glass window, and other frames. The cover glass is made of quartz. Most of the radiation power from the plasma is contributed by vacuum ultraviolet light. For example, the Lyman alpha line of C5+ (wavelength is 3.37 nm) attenuates to 1% at a thickness of 2 μm from the surface of the quartz glass.4 Therefore, the cover glass can work as a heat shield for the sapphire glass. The cover glass is supported by a polybenzimidazole (PBI) plastic frame. PBI has a similar linear expansion coefficient value to the quartz glass, which reduces thermal stress in the cover glass. The vacuum flange with sapphire glass window was selected based on a shock test of 60 G (Ref. 5) and operating in the JT-60U. The sapphire glass is brazed with Ag-Cu to a KOVAR sleeve made of Fe-Ni-Co alloy. The maximum temperature of the vacuum flange with sapphire glass window is limited to 300°C by the KOVAR sleeve.
Analytical thermal stress modeling in electronics and photonics engineering: Application of the concept of interfacial compliance
Published in Journal of Thermal Stresses, 2019
A novel method for the compensation of temperature induced changes in optical devices has been patented in [23]. In a preferred embodiment, the method and apparatus are directed toward compensation of fiber optic cable to remove the effects of temperature-induced changes, on system performance. The method can be applied to temperature-sensitive devices other than refractive index (Bragg) gratings in optical fibers: applications to a musical instrument string or a pressure relief valve are just a few examples. In general, any temperature-sensitive device, the performance of which may be adjusted by tension or compression, may be mounted on a thermostatic compensation device made according to the method of the invention to compensate for the change of performance with temperature. Materials suitable for use in fabricating the invention include ceramics, glass, Kovar, and Invar. To maximize the curvature of the thermostatic elements, bi-material thermostats which include a ceramic with a negative CTE may also be employed. The use of a ceramic material increases the difference in CTE of the two materials constituting the thermostatic elements and thus provides for greater curvature in response to temperature changes.