Spatially Resolved Thermal Conductivity of Intermetallic Compounds Measured by Micro-Thermoreflectance Method

Abstract

Spatially resolved thermal conductivity of Cu 6 Sn 5 intermetallic compounds (IMCs) formed in Sn Ag Cu lead free solder has been investigated by using a periodically modulated thermoreflectance (TR) method. The high spatial resolution has been achieved by focusing a modulated laser beam. The temperature response on the irradiated surface has been analyzed by calculating the phase lag of the TR signal as a function of the thermal diffusion length. We found that the boundary of IMCs influences the phase lag. Furthermore, the thermal conductivity of Cu 6 Sn 5 was selectively measured by the TR method considering three dimensional thermal diffusion model. The estimated thermal conductivity of Cu 6 Sn 5 is 39 W/(mK) which is lower than 54 W/ (mK) of Sn 3.5Ag 0.5Cu. Thus the micro TR method is a powerful method to characterize the thermal conductivity of not only IMCs but also various complex materials.

Evaluation of the thermal effusivity of intermetallic compounds using a modulated thermoreflectance method

“…25) And Sn-3.5Ag-0.5Cu exhibits a value slightly higher than the average thermal effusivity of Sn-3.5Ag-0.5Cu solder bulk materials (9641 J s −0.5 m −2 K −1 ) with the same elemental composition. 6) The reason why the thermal effusivity of Sn-10Sb is smaller than that of Sn-3.5Ag-0.5Cu is the addition of Sb. It is considered that the addition of Sb (23 W m −1 K −1 ) reduces thermal conductivity based on the generation of a substitutional solid solution between Sn and Sb according to the compositions listed in Table I and heating conditions.…”

“…Since κ is a physical property, the thermal diffusion length will have a frequency dependence when measuring a single material. 6) Therefore, we can choose to include or exclude the interface of the IMCs in the measurement range by changing the frequency, allowing us to evaluate the thermal effusivity and interface of the IMCs.…”

“…Additionally, morphological changes at the interface during aging are also based on the initial morphology. 6) The growth of IMCs is also affected by reflow conditions. Because both the mechanical and electrical properties of IMCs are significantly different from those of Sn and Cu, excessive growth or unexpected morphological changes in IMCs layers in the fine joint structures of electronic components may deteriorate the mechanical and electrical quality of jointed structures.…”

“…These techniques measure the entire sample, whereas the thermoreflectance (TR) method is a measurement method in which a laser beam is focused to a few micrometers by an objective lens and the thermal properties of the region under the laser are measured. 2,6,[14][15][16][17][18][19][20][21][22] In this method, the temperature dependence of the reflectance of the target metal is used for measurement. Over the past few decades of research on the TR method, metal thin films have played an essential role as reflectors.…”

Mechanical and Physical Properties of Hybrid Cu-Graphite Composites Prepared via Powder Metallurgy Technique

“…Thermal and electrical conductivity of Sn and Cu6Sn5 are 227W/(K.m), 21.7 (μΩ. m) -1[20] and 39W/(K.m)[25],5.7(μΩ.m) -1[26,27] respectively. While thermal and electrical conductivi-ty of copper are 397 W/(K.m) and 60 (µΩ.m) -1 respectively[20].…”