Optimization of Copper Thermocompression Diffusion Bonding under Vacuum: Microstructural and Mechanical Characteristics

Abstract

The optimization of the autogenous diffusion copper bonding via thermocompression at vacuum environment was investigated. The influence of various bonding parameters on the interdiffusion efficiency was studied in detail at the micro (SEM-EBSD) and nano (TEM) scales. Bonding at 1000 °C for 90 min under pressure (10 MPa) presented optimum structural and mechanical results. Under these conditions, interdiffusion phenomena were observed at a significant extent through the swelling transformation of existing fine grains or the formation of equiaxed copper grains with an orientation parallel to the bond interface. Transmission electron microscopy revealed the importance of the grain size of the base material on the bond quality. In the regions with fine-sized copper grains, the formation of small equiaxed recrystallized twins was observed. Their length within the bonding zone was in the order of 200 and 400 nm. On the contrary, in the regions with coarse grains the interdiffusion was poorer. The processing temperature and duration presented a significant effect on the bonding strength (BS). BS exceeded 100 MPa in case of processing conditions of T ≥ 850 °C and t ≥ 60 min, while the maximum BS value achieved (≈180 MPa) was comparable with the respective value of the base material. The microhardness of the optimum bond reached 55 HV—slightly higher in comparison to the hardness of the initial copper material. The results indicated that the proposed thermocompression process is appropriate for the production of Cu-Cu bonded structures that can be potentially used as electrical components under mechanical stress.

Impact of the Samples’ Surface State on the Glow Discharge Stability in the Metals’ Treatment and Welding Processes

“…Denote it by β E , then the expression (6) can be written as E(x) = E av β E . The term in parentheses of expression (6) is always less than one and on the surface of the protrusion at x = h vanishes. Therefore, the main is the second term, the value of which is maximum at minimum x, i.e., at x = h and at the x = d c simultaneously.…”

“…Known works consider the possibility of application of gas discharges technique in the field of thin films deposition, metals surfacing, treatment and modification of metals before welding [2][3][4][5]. Still, as practice has shown, diffusion welding [6] and thermal and chemical-thermal surface treatment [7] are the most appropriate. This is due to the high technological capabilities of the glow discharge, which in these processes can serve both a processing tool and a source of thermal energy for their implementation simultaneously.…”

Microstructure and Tensile Properties of Diffusion Bonded Austenitic Fe-Base Alloys—Before and After Exposure to High Temperature Supercritical-CO2

“…It is well known that the quality of a diffusion bond is sensitive to various bonding parameters such as temperature, pressure, and duration, as also indicated in the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code, Section IX under Part QW. In addition, selecting optimum diffusion bonding conditions would differ for varying alloys, and would involve consideration of each alloys' mechanical properties, microstructures, and chemical composition [18,19]. For example, Gietzelt et al conducted diffusion bonding on austenitic, ferritic, and martensitic stainless steels and reported that the highly alloyed steels required more severe conditions for a sound diffusion bond to be achieved [20].…”