D-MAX DMC-20SEC Manual de usuario descargar pdf (Pagina 19)

lead-based solder alloys – which are much more even and mirror-like – they reflect light

differently, so different procedures may be used to verify the presence and quality of the solder

menisci.

In the case of tin-lead solders, the solidification of the melt begins around the cores that are

solid at melting point, and the individual solid phases grow at a virtually consistent rate as

the two elements separate from the melt. This is how the volumes that are rich in lead and tin

become a smooth-surfaced alloy consisting of lead and tin patches, typical of eutectic solder,

that can easily differentiated on the cross-section.

Lead-free solders do not usually form eutectic alloys, and exist in many variants with different

compositions. Tin is usually alloyed with copper and silver, but there are also alloys containing,

for example, bismuth and indium.

In the case of the non-eutectic alloys (the vast majority of lead-free alloys), however, one of the

phases begins to solidify earlier, and the alloying metal concentration of this phase will be

smaller than that of the melt. This means that the composition of the remaining part of the

alloy, which is still in a liquid state, continues to change until the eutectic composition is

Figure 7. Tin-lead phase diagram

Automatic Optical Inspection of Soldering

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

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D-MAX DMC-20SEC Manual de usuario Pagina 19