D-MAX DMC-20SEC Manual de usuario descargar pdf (Pagina 24)

alloys is even more visible. In the following SEM images the rough surface typical of lead-free

solder alloys can be observed.

Figure 14. SEM image of a cross-section of a lead-free solder meniscus

The fracture in the solder meniscus seen in the above image is probably due to a contaminant,

but within the fracture is a particularly clear example of just how uneven a surface can be

formed by the lead-free solder alloy.

The surface roughness of the lead-free solder meniscus is visibly greater than that of the tin-

lead solder. Taking the scale bar as a guide we can also estimate that the size of the uneven

protrusions that increase the surface roughness, in terms of both their breadth and height, is

in the order of 10 μm. It is also worth noting that the simplification of the microfacet model

described by the Cook-Torrance model is clearly visible, as a visual inspection reveals that the

surface is not closely similar to the surface made up of tiny flat plates that is assumed by the

microfacet model. This simplification, however, is more than made up for by the model’s

simplicity and general ease of use.

7.2. Measuring the surface roughness

To measure the surface roughness we used a Tencor Alpha Step 500 surface profilometer. Based

on the 10 measurements of each solder, made on the lead-based (Heraeus F816 Sn63-90 B30)

and lead-free (Senju Ecosolder M705-GRN360-K1-V) joints, the two solders yielded the

following values:

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D-MAX DMC-20SEC Manual de usuario Pagina 24