Solder physical properties

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. 

Solders should flow promptly and smoothly over the surfaces of the parts to be joined. This property depends on the surface tension, viscosity, and adhesive properties of the molten solder. Finally, the color of a solder should match that of the metal employed, and its physical properties should be at least as good as those of the metal, in order for the joint not to be a source of weakness (150). 

The predicted behaviour of individual liquid metals depends on their specific physical properties, such as those listed in Table 10.1 for Hg and a number of solder and braze metals and alloy solvents. Substitution of these values into... 

The physical properties of many metals render them unsuitable for fabrication and engineering purposes. By combining two or more metals, or metals with non-metals, one can form alloys with enhanced properties such as strength, malleability, ductility, hardness or resistance to corrosion. For example, adding Sn to Pb gives Pb-based alloys with applications as solders by varying the Pb Sn ratio, the melting point of the solder can be modihed and tailored to the needs of particular applications. 

PUC] Physical properties tests Solderability, surface roughness, brightness, bondability... 

The accepted method of nondestructive testing used to control the underfill process is SAM. The thin layer allows this technique to detect voids in the underfill material, which when located near the solder interconnections can be responsible for a significant loss of thermal mechanical fatigue reliability. X-ray techniques can be used to monitor the density of the underfill material, specifically, the distribution of filler material within the layer under the die. Density variations can indicate a larger distribution of underfill mechanical and physical properties, which may affect long-term reliability performance of the solder joints. Quantitative image analysis can be coupled into SAM and x-ray analysis data to provide valuable process control tools for the factory floor. 

To understand the issues of solderability it is first important to understand what is meant by the term, including appropriate definitions, the physical properties of the materials involved, and the various standards developed to guide the user to ensure that the solder process will... 

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