In-situ observation of high-temperature Pb-free electric interconnections by synchrotron microradiography

Controlling Pore Position during Transient Liquid Phase Bonding for High-temperature Soldering Processes

“…This method can be used to redistribute microvoids and avoid the agglomeration of porosities in a plane parallel to the substrate in the joint. [23,24] This finding is consistent with previous research, which shows that pores move in response to the growth of IMCs. [23,24]…”

“…The voids in the joint are linked to the shrinkage of solder volume during solidification, [28] the unbalanced diffusion and partial molar volume change between Sn and Cu, [29,30] the formation of Kirkendall voids during the growth of Cu 3 Sn [29,31] and/or trapped gas from the flux chemical reaction. [32][33][34][35] These microvoids and large pores became trapped in the middle of the joint between the IMCs that grew from the top and bottom of the joint [23] as shown in Fig. 1 (b).…”

“…1(b), as demonstrated using real-time X-ray microradiography synchrotron observation of a Cu-6Ni/Sn-Cu/Cu-6Ni TLP connection. [23] In this earlier study, despite achieving rapid growth of the IMC, the presence of microvoids at the liquid/IMC interface and pore formation from gas entrapment were identified as potential issues in practical applications. The presence of trapped gases, which is likely stemming from solvent evaporation or the inclusion of rheological additives in the flux, then tends to accumulate at the solder-substrate interface, thereby fostering void formation.…”

“…We have previously investigated these two main problems, which are summarised in Fig. 1, [15,[22][23][24] and proposed a novel production method to obtain a high-temperature joint while minimising processing times and the impact of porosity.…”

“…1(a). [15,22,25,26] By adding 6 wt.% nickel (Ni) to a Cu substrate (Cu-6Ni) the IMC growth rate at equivalent temperatures is greatly accelerated, [15,22,23,27] reducing the TLP processing time as shown in Fig. 1(b), as demonstrated using real-time X-ray microradiography synchrotron observation of a Cu-6Ni/Sn-Cu/Cu-6Ni TLP connection.…”