D-MAX DMC-20SEC Bedienungsanleitung PDF herunterladen (Seite 25)

Type of measurement result Lead-based solder paste Lead-free solder paste

Measured surface roughness (RMS) 0.03092 0.0986

Distribution of measured RMS value 0.004451 0.054626

Table 11. Measured surface roughness values

At first glance the measured surface roughness values appear realistic; the surface roughness

of the lead-free solder turned out to be approximately three times that of the lead-based solder.

The distribution of the roughness values for the lead-based solder was below 1%, which is

satisfactory because the divergence between the shape of the actual solder and that modelled

by the computer showed a greater error (a few percent), and because greater fluctuation than

this can be expected to result from the differing heat profiles, printed circuit boards or solder-

handling requirements of real production lines. The distribution of the surface roughness

values for the lead-free solder was over 5%, which is due to diversity of the size and shape of

the surface protrusions that appear with this type of solder, which the Cook-Torrance model

handles using statistical simplification, by assuming the surface to be of a consistent roughness.

7.3. Simulation created with the computer model

We checked the measured surface roughness values by comparing the images made using

optical microscopes with the computer-generated graphic representations. The Surface

Figure 15. SEM image of a cross-section of a lead-free solder meniscus

Automatic Optical Inspection of Soldering

http://dx.doi.org/10.5772/51699

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D-MAX DMC-20SEC Bedienungsanleitung Seite 25