Thermal Conductivity of Molten Lead-Free Solders

Abstract

The paper reports measurements of the thermal conductivity of a number of molten solders for the electronics industry that are part of a group of materials designed to be free of the toxic problems associated with lead-based solders. The measurements have been carried out with a transient hot-wire instrument originally designed for the measurement of the thermal conductivity of pure molten metals. In the application reported here the instrument has been used largely unchanged but an improved finite-element code has been used for the analysis of the raw data so as to yield the thermal conductivity of the molten solders. The measurements extend from the melting point of the solder up to 625 K. The uncertainty in the thermal conductivity measurements is estimated to be no larger than 3%.

Hybrid 3D Printing of Molten Metal Microdroplets and Polymers for Prototyping of Printed Circuit Boards Featuring Interdigitated 3D Capacitors

“…For this purpose, SAC305 bulk metal is heated in the StarJet printhead reservoir at 320 • C and dispensed, forming microdroplets of diameter (280 ± 6) μm. These droplets are dispensed on (a) PC-FR surface causing slow cooling because of the difference in the thermal conductivity of the two materials (K SAC305 = 58 W/(m•K) [13]; K PC-FR = 0.20 W/(m•K) [14]) (b) dispensed in deionized water. The variation in oxygen percent at different print conditions is observed using EDS.…”

Thermophysical Property Measurements: The Journey from Accuracy to Fitness for Purpose

“…A circular section platinum wire is contained on the central plane of a sandwich made from two alumina ceramic elements, and this planar substrate structure is immersed in the molten metal for which the thermal conductivity is desired. As in the transient hot-wire method, a current is passed through the platinum wire and the temperature rises at a rate that is initially determined by the thermal conductivity and heat capacity of the metal itself, then that of the surrounding substrate, and eventually of the molten metal [126,127]. The difference, of course, is that there is no direct contact, either electrical or thermal, between the hot wire and the molten metal.…”

“…modeling to describe this heat transfer process. For that purpose, the complete system is divided into a series of meshes that accounts for the fact that there is a mixture of geometry between the circular wire and the rectangular elements, and a finite element model based upon conventional Fourier equations can be built and solved as described elsewhere [124,126,127]. It is then possible to predict from assumed values of the thermal conductivity, heat capacity, and density of the wire, the substrate, the molten metal and, if necessary, any interface elements, the temperature history of the wire subject to a transient heat input.…”

Measurements of the Thermal Conductivity of Molten Lead Using a New Transient Hot-Wire Sensor

“…The sudden changes in time-stepping employed earlier have been removed and the FE model becomes even more accurate. The detailed features of the upgraded FE model, the fundamental mathematical equation as well as the validation of the FE model, have been presented elsewhere [5][6][7][8][9].…”

“…This new design has been tested in a number of experiments with molten indium, tin, and various solder alloys and the results compared to the values obtained from measurements of the thermal conductivity using the original design [7][8][9]. Both the new and old sensor designs provided similar results with deviations of no more than 2%, which is less than the mutual uncertainty.…”