Kinetic analysis of the soldering reaction between eutectic SnPb alloy and Cu accompanied by ripening

Abstract

The wetting reaction of molten eutectic SnPb on Cu leads to Cu-Sn intermetallic compound formation, but not compounds of Cu-Pb since they do not exist. Cu-Sn compounds do not form layered structures between the solder and Cu, rather the Cu 6 Sn 5 phase has grown as scalloplike grains into the molten solder. The scalloplike grains grow larger but fewer with time, indicating that a ripening reaction has occurred among them. However, the ripening is not a constant volume process since it is accompanied by the soldering reaction. Between the scallop grains, there are molten solder channels extending nearly all the way to the Cu interface. In aging, these channels serve as fast diffusion and dissolution paths of Cu in the solder to feed the reaction. A kinetic analysis of the soldering reaction accompanied by the ripening reaction is given. In the analysis, the growth of the scalloplike grains is supplied by two fluxes: the flux of interfacial reaction and the flux of ripening. The latter was formulated by the Gibbs-Thomson equation. The former was obtained by measuring the rate of consumption of Cu in the reaction. The measurement was carried out by determining the change of the total volume of scalloplike grains ͑and in turn, the Cu content in the grains͒ as a function of time and temperature. A reasonable agreement has been obtained between the calculated scallop-grain growth based on kinetic analysis and the experimentally measured values. A discussion of the Cu consumption rate is given, since it is important for applications in electronic packaging technology.

Effect of Zn Addition on Interfacial Reactions Between Sn-4Ag Solder and Ag Substrates

“…Generally speaking, the interface between the solder and the IMC, rather than that between the IMC and the substrates, is always rough because it is the foreland of the reaction. 30 However, the opposite result was obtained in our research. Firstly, some Sn-rich regions were found under liquid-state conditions, which is different from the interfacial reactions between most lead-free (e.g., Sn-In) solders and Ag substrates, 24,26,31 as displayed in Fig.…”

Continuous epitaxial growth of extremely strong Cu6Sn5 textures at liquid-Sn/(111)Cu interface under temperature gradient

“…Thus, sharp edges in a faceted prism-type g-Cu 6 Sn 5 crystal tend to dissolve to minimize the curvature effect (surface area) to form the round scallop-shaped morphology via the coalescence process-Ostwald ripening. 23 Thermomigration is one of the simultaneous heat and mass transfer phenomena that occurs in a mixture, as a result of an external temperature gradient imposed across the mixture. The thermomigration flux J TM of Cu atoms under a temperature gradient dT/dx can be written by…”

Formation and Growth of Intermetallic Compound Cu6Sn5 at Early Stages in Lead-Free Soldering

“…[4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] These works suggest that, upon contact, Cu and liquid Sn react to form two distinct IMCs [Cu 6 Sn 5 (g phase) and Cu 3 Sn (e phase)], which precipitate at different stages of the soldering reaction. Most research seems to suggest that, at the very early stages of the soldering reaction, the g phase precipitates first.…”

“…19 Earlier works have focused on experimental characterization of the late stages of growth and coalescence of g and e phases during lead-free soldering reactions between Sn and Cu. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] More recently, several groups have investigated the formation of the g phase at the early stages of soldering reactions. [20][21][22][23] These latter works have found that individual Cu 6 Sn 5 grains seem to appear at random positions along the (metastable) solid/liquid interface within a few milliseconds.…”