Study of Undercooling and Recalescence During Solidification of Sn62.5Pb36.5Ag1 and Sn96.5Ag3Cu0.5 Solders in Real Electronic Joints
Autor
Rudajevová, A.
Dušek, K.
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Undercooling and recalescence were studied using the differential scanning
calorimetry (DSC) method on real electronic systems. Two solder pastes,
Sn62.5Pb36.5Ag1 and Sn96.5Ag3Cu0.5, were used for preparation of electronic
joints. Various combinations of these solders and soldering pads with different
surface finishes such as Cu, Cu-Ni-Au, Cu-Sn, and Cu-Sn99Cu1 were used.
During melting of both pastes, the Sn and Sn99Cu1 surface finishes immediately
dissolved in the solder and the Cu surface coating was exposed to the
melt. Therefore, practically the same undercooling was found for the Cu,
Cu-Sn, and Cu-Sn99Cu1 coatings. The lowest undercooling was found for the
Cu-Ni-Au surface finish for both solder pastes. If two separated electronic
joints were made on the sample, two separate peaks were found in the DSC
signal during solidification. In the sample with only one joint, only one exothermic
peak was found. These findings were observed for all paste/surface
finish combinations. These data were analyzed, showing that this effect is a
consequence of undercooling and recalescence: Latent heat released during
solidification of the joint increases the surrounding temperature and influences
all the processes taking place.
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