Study of Undercooling and Recalescence During Solidification of Sn^sub 62.5^Pb^sub 36.5^Ag^sub 1^ and Sn^sub 96.5^Ag^sub 3^Cu^sub 0.5^ Solders in Real Electronic Joints

• Published in: Journal of electronic materials 2014-07, Vol.43 (7), p.2479
• Main Authors: Rudajevová, A, Dusek, K
• Format: Article
• Language: English
• Subjects: Alloy solidification; Electronics; Lead free solders; Materials science
• ISSN: 0361-5235; 1543-186X
• DOI: 10.1007/s11664-014-3121-6

Undercooling and recalescence were studied using the differential scanning calorimetry (DSC) method on real electronic systems. Two solder pastes, Sn^sub 62.5^Pb^sub 36.5^Ag^sub 1^ and Sn^sub 96.5^Ag^sub 3^Cu^sub 0.5^, 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-Sn^sub 99^Cu^sub 1^ were used. During melting of both pastes, the Sn and Sn^sub 99^Cu^sub 1^ 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-Sn^sub 99^Cu^sub 1^ 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.[PUBLICATION ABSTRACT]