Solder thermal conductivity

Ki (W/m.K) - solder thermal conductivity Gaussian Mean = 25 Standard dev = 0.05 mean... 

Solders. In spite of the wide use and development of solders for millennia, as of the mid-1990s most principal solders are lead- or tin-based alloys to which a small amount of silver, zinc, antimony, bismuth, and indium or a combination thereof are added. The principal criterion for choosing a certain solder is its melting characteristics, ie, soHdus and Hquidus temperatures and the temperature spread or pasty range between them. Other criteria are mechanical properties such as strength and creep resistance, physical properties such as electrical and thermal conductivity, and corrosion resistance. 

Stainless steels are iron-based alloys which contain more than 12% chromium. A common composition contains 18% Cr and 8% Ni, and is designated as either 18 8 or type-304 stainless steel. Unlike ordinary carbon steel, the stainless steels in the 300 series do not become brittle at low temperatures. Stainless steel has a rather low thermal conductivity. It may be welded, brazed, or soldered and is machinable with some difficulty. Type 303 is the easiest to machine. 

B. Copper. Copper (mp 1,083°C), is a moderately soft metal which has a high electrical and thermal conductivity. Electrolytic copper, 99.9% pure, is used for electrical wire and free-cutting alloys, containing small amounts of sulfur or tellurium, are commonly used for sheet or bar stock. Copper may be machined, brazed, and soldered. However, because of its toughness, it is much less easy to machine than brass. It tends to work-harden but may be annealed by heating, followed by rapid quenching. 

For chips mounted face up, heat is transferred to the substrate by conduction through the interconnection layers, and because the polymer dielectric has poor thermal conductivity, heat conduction is often promoted by an array of metallized vias through the interconnection layers (Figure 16) (100). For face-down-mounted chips, the heat may be removed from the back side by using pistons (as in the TCM) or conductive fluids, or heat may be conducted through the solder bonds to the interconnection substrate (98). 

Several of the low-temperature superconducting metals, such as lead, brass, and some solders (particularly lead-tin alloys), experience property changes when they become superconducting. Such changes can include specific heat, thermal conductivity, electrical resistance, magnetic permeability, and thermoelectric resistance. Consequently, the use of these superconducting metals in the construction of equipment for low-temperature operation must be evaluated carefully. 

The coefficient of hydride bed effective heat transfer aef is proportional in general to layer effective thermal conductivity and inversely proportional to layer thickness. The analysis of this equation shows that the heat transfer coefficient is less than a smaller coefficient of heat emission and, consequently, it is meaningless to increase strongly one of them without changing the other. The experimental results show that for the soldered and diffusion welded connections of sorber case and heat-conducting insertion R = (0.5-1.5)-10 5 (m2 K)/W. If contact between insertion and a case is tight fit, then R increases in 10-100 times and influence of contact resistance becomes comparable with influence of reduced heat emission of a hydride bed. 

In the process of constructing a thermocouple, two thin wires of different thermal conductivity are soldered with a heat flux q" applied locally. Express q" in terms of the melting temperature of the solder. Data Wire diameter d = 1 mm, ambient air temperature Tea = 20 °C, melting temperature Tm = 260 °C, conductivity of the wires k = 20, k2 = 60 W/mheat transfer coefficient h = 10 W/m -K. 

The backmetal schemes investigated primarily remove heat via the conduction method. Both copper and silver possess excellent thermal conductivity properties, which are beneficial for heat dissipation. Device solderability to a package, which also strongly influences the heat dissipation, was not effected by the Ta/Cu metal scheme. The three key parametric areas examined, which included packaging, Vsd and Rdson all showed that the Ta/Cu metal scheme is a viable alternative without altering the current packaging process. 

Bismuth is the most diamagnetic of all metals and has low thermal conductivity. Since bismuth expands upon solidification, it is used to make castings for objects subjected to high temperatures. It is used as a replacement for lead in solders, shot for hunting, fishing sinkers, ceramic glazes, and brasses for plumbing applications. It is also used as a carrier for (an isotope of uranium) fuel in atomic reactors. Ionic compounds of bismuth are used in cosmetics and medicine. 

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