Early stages of soldering reactions

Abstract

An experiment on the early stages of intermetallic compound layer growth during soldering and its theoretical analysis were conducted with the intent to study the controlling factors of the process. An experimental technique based on fast dipping and pulling of a copper coupon in liquid solder followed by optical microscopy allowed the authors to study the temporal behavior of the sample on a single micrograph. The technique should be of value for different areas of metallurgy because many experiments on crystallization may be described as the growth of a layer of intermediate phase.Comparison of the experimental results with the theoretical calculations allowed one to identify the kinetics of dissolution as the rate-controlling mechanism on the early stages and measure the kinetic coefficient of dissolution. A popular model of intermetallic compound layer structure coarsening is discussed.

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

“…The number of IMC grains decreases (IMC microstructure coarsening) only at the later stages of the soldering reaction. This is consistent with the experimental observations by Lord and Umantsev 21 and Gorlich and Schmitza. 18 At later stages of the soldering reaction the grain boundaries are grooved, and partial penetration (wetting) of the g grain boundaries is observed.…”

“…3a and b). 21 In the case of higher simulation temperatures ( Fig. 3c and d), fewer nuclei are nucleated due to lower nucleation driving forces, and the nuclei are likely to grow in width rather than in height.…”

“…(2) After grains impinged, the scallop shape of the grains can be observed, which results from grain coarsening. 21,25 (3) Although the formation and growth of the IMC grains were observed to be somewhat different from in the research by Huh et al 25 during early stages, the behavior of the IMC grains (or layer) applied with different material parameters (e.g., D GB ) at the late stages eventually appears similar to in the research by Huh et al 25 (4) Although the differences seem slight, the number of g grains per unit area increases with increase of reaction temperature until between 260°C and 270°C, and then decreased afterward regardless of nucleation conditions, which is in good agreement with experimental results. 20 Finally, comparison between simulations and experiments 20 suggests that the actual grain boundary diffusion coefficient in g grains is at least two orders of magnitude higher than the diffusion coefficient in bulk g grains.…”

“…[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. After the g grains appear, they have been found to spread along the interface without much growth perpendicular to the solder/substrate interface until they meet with other spreading grains, forming a relatively uniform IMC layer of Cu 6 Sn 5 .…”

Modeling of intermediate phase growth

“…To resolve the problem of the mechanism of IMC layer formation and growth, Lord and Umantsev 10 conducted an experiment with the intent to capture the growth on the very early stages. Fast dipping and pulling of a copper coupon in liquid solder allowed the workers to study motion of the boundaries of the layer relative to the original solder/contact interface, the base line.…”