Intermetallic phase detection in lead-free solders using synchrotron x-ray diffraction

Abstract

The high-intensity, high-resolution x-ray source at the European Synchrotron Radiation Facility (ESRF) has been used in x-ray diffraction (XRD) experiments to detect intermetallic compounds (IMCs) in lead-free solder bumps. The IMCs found in 95.5Sn3.8Ag0.7Cu solder bumps on Cu pads with electroplated-nickel immersion-gold (ENIG) surface finish are consistent with results based on traditional destructive methods. Moreover, after positive identification of the IMCs from the diffraction data, spatial distribution plots over the entire bump were obtained. These spatial distributions for selected intermetallic phases display the layer thickness and confirm the locations of the IMCs. For isothermally aged solder samples, results have shown that much thicker layers of IMCs have grown from the pad interface into the bulk of the solder. Additionally, the XRD technique has also been used in a temperature-resolved mode to observe the formation of IMCs, in situ, during the solidification of the solder joint. The results demonstrate that the XRD technique is very attractive as it allows for nondestructive investigations to be performed on expensive state-of-the-art electronic components, thereby allowing new, lead-free materials to be fully characterized.

In situ investigation of the interfacial reaction in Sn/Cu system by synchrotron radiation

“…In situ investigation of the interface reaction of solder joints during reflow is limited in the literature, and the formation of IMCs has not yet been discussed completely. 3 During daily usage of the 3C consuming product, constant operation of On/Off in products can be considered as temperature cycling. The mismatch of coefficient of thermal expansion (CTE) among solder, substrate, and IMCs would introduce the thermal-mechanical stress and finally the product would fail due to the stress.…”

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

“…In addition, five possible graphite peaks are present in this window, as indicated. The two most prominent high-angle Sn peaks are Sn(200) located at 2.916 Å and Sn(101) located at 2.793 Å , as calculated from the lattice parameters of bct Sn for a = 5.8313 Å and c = 3.1815 Å , 18 for the 29.1-keV beam. Texturing of the thin foil results in only the Sn(101) peak diffracting strongly in this case, and alters the ideal diffraction intensities of the remaining six peaks that appear at lower d-spacings.…”

“…New experimental methods such as in situ x-ray diffraction are beginning to be used to help understand microstructural and intermetallic compound (IMC) formation in solder alloys and solder joints. 17,18 This paper continues along these lines, using in situ x-ray diffraction to study Sn and In melted and solidified on different substrates to directly observe the amount of undercooling prior to solidification. In addition, anisotropic lattice expansion of the tetragonal crystal structures of In and Sn was measured during heating and cooling, as well as lattice expansion for IMCs that formed between Sn and the Au/Ni/Cu substrate.…”

In Situ Synchrotron Characterization of Melting, Dissolution, and Resolidification in Lead-Free Solders

“…8 Synchrotron x-ray diffraction has been used to investigate the Sn and IMC characteristics during melting and solidification. [9][10][11][12] In the present work, the focus is on the melting and solidification of Sn in Sn-3.0Ag-0.5Cu (wt.%) (SAC305) lead-free solder balls in a wafer-level chip-scale package (WLCSP). With a high-energy monochromatic x-ray beam, diffraction patterns sampled from the whole volume of solder balls and interface metallurgy were collected every 0.5 s during melting and solidification.…”