Cyclic twin nucleation in tin-based solder alloys

Effects of cobalt on the nucleation and grain refinement of Sn-3Ag-0.5Cu solders

“…When all βSn grains inside a ball grid array(BGA) solder joint are related by one common axis, the whole joint will respond mechanically as a single crystal along the common axis and a polycrystal along other directions [5]. Therefore, there is an interest in developing methods to control the nucleation undercooling of βSn as well as the number and orientation of grains in solder joints.…”

“…In Sn, most twins and CSL boundaries have a common <100>, <001> or <110> direction [5,51] and, therefore, we identified independent grains by first checking for any common <100>, <001> or <110> axes and then, if necessary, checking whether the misorientation around that axis is consistent with a known twin or CSL boundary. Figure 11 A summary of the number of independent Sn grains in balls and joints is given in the pie charts in Figure 11(g) for the three solder compositions, at four cooling rates spanning ~5-17K/s (representing >200 samples).…”

“…It is well known that Sn-Ag-Cu (SAC) solder joints usually solidify after a relatively large nucleation undercooling for βSn (~10-30 K) which can cause problems such as large primary intermetallic phases and only a single βSn nucleation event, producing single grain or cyclically-twinned joints [1][2][3][4][5]. For example, the large plate-like primary Ag 3 Sn can provide crack initiation sites and have been linked with poor mechanical behaviour of solder joints [6][7][8][9], and a small number of βSn grains per joint render the joint anisotropic in thermal expansion and mechanical properties as βSn has highly anisotropic thermophysical…”

Influence of Bi additions on the distinct βSn grain structure of Sn-0.7Cu-0.05Ni-xBi (x = 0–4wt%)

“…Misorientation histogram shown in Figure 1 further proves that all grains are twinned suggesting that there was only one nucleation event in the solder joint. This result is well known and the origin of solidification twinning is discussed in [10,12] observed in all ten SAC305/Cu solder joints produced in this study: it was either a single βSn grain or a twinned structure.…”

Measurement of Sn and In Solidification Undercooling and Lattice Expansion Using In Situ X-Ray Diffraction

“…Indium, on the other hand, displays very little undercooling and solidifies close to its equilibrium melting point on all of the surfaces studied. Reducing the amount of undercooling of Sn and Sn-based solder alloys prior to solidification is an area of great interest to improve mechanical properties of lead-free joints, [4][5][6][7][8][9][10][11][12][13][14] and future work is planned to use the in situ diffraction experiments developed here to investigate the influence of various inoculants on reducing undercooling in Sn and Sn-based solder alloys.…”