Study of silver-copper-palladium solder properties for vacuum electronic devices

Silver-Copper-Palladium (Ag-Cu-Pd) brazing alloy is an important material used for vacuum electronic devices packaging for its low vapor pressure, good air tightness, excellent wetting property, and mechanical properties. The Ag-Cu-Pd brazing alloys are proposed for the vacuum electronic devices packaging in these few years. Ag-Cu-Pd alloy is one of the common mid-temperature and high-temperature brazing alloys used in multiple temperature gradients soldering as present. In the current study, three Ag-Cu-Pd brazing alloys with different components were designed for multiple temperature gradient soldering. The Ag-Cu-Pd brazing alloys were prepared by means of vacuum induction melting. In order to obtain thin Ag-Cu-Pd alloy strips, the ingots were melted and injected onto a copper roller rolling at high speed (i.e., melt spinning). The obtained thin strips were used for soldering. The phase constitution, solidliquid phase transition temperatures, microstructures, elemental distribution and wetting property of the Ag-Cu-Pd solder alloys on copper were investigated. Melting behavior of three Ag-Cu-Pd brazing alloys with different components were tested using Differential Scanning Calorimetry, the liquidus were 990°C, 890°C and 846°C. The Ag-Cu-Pd brazing alloys were soldered with copper substrates at different temperatures for different periods of time. The spreading areas for all Ag-Cu-Pd brazing alloys on copper were in the range of 220-460 mm², the wetting angles were in the range of 12-24°, which indicate the good wettability of Ag-Cu-Pd alloys on copper. The Cu/Ag-Cu-Pd solder joints were examined with Scanning Electron Microscope and Electron Dispersive X-ray analysis. In this study, the proper vacuum electronic devices brazing components and optimal brazing parameters are obtained, which could be potentially applied for practical applications.