D-MAX DMC-20SEC Bedienungsanleitung PDF herunterladen (Seite 22)

An important question is precisely what the roughness of the pattern formed on the surface

of lead-free solder alloys depends on, and how “reliably” predictable the process of its

formation is.

Figure 11. SEM image of the surface of a lead-free solder meniscus

In the above image the two types of solder can be clearly differentiated due to the rougher

surface that is typical of the lead-free alloy. In places the surface looks quite similar to the one

assumed by the microfacet model, which simplifies reality for the purpose of mathematical

manageability; in other words, small semi-spherical formations can be observed side by side

with each other. On other parts of the picture, however, areas with no unevenness are also

visible; and we have taken the electron microscope image of an area that gives a good

illustration of a particular property of lead-free, non-eutectic solder alloys (in this case a tin-

copper-silver alloy), namely that due to the unevenness of the surface it reflects the light more

diffusely (in other words, it scatters the light more) than the smoother surface of a eutectic

solder. In the applied Cook-Torrance model, the roughness of the surface is described by a

single parameter, which describes the surface in average terms.

The above picture shows an SEM image of a cross-section in which the tin (light) and lead

(dark) phases of the eutectic alloy are clearly differentiated.

The above image was made at a lower magnification (400x rather than 1500x), but the phase

boundaries can still be made out, and the smooth meniscus surface typical of lead-based solder

Materials Science - Advanced Topics

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D-MAX DMC-20SEC Bedienungsanleitung Seite 22