I believe that any industry engaged in electronic production, processing, and research and development is familiar with tantalum capacitor recycling, as its unique characteristics make it widely applicable.

The properties of tantalum metal

In 1802, the rare metal tantalum (Ta) was discovered by AG Ekeberg and is located in the VB family of the periodic table [2]. It has an atomic number of 73 and an atomic weight of 108.195. It belongs to the body centered cubic structure, with a lattice constant of A: 3.2959, a melting point of 2996 ℃, and a boiling point of 5427 ℃, ranking third only to tungsten and rhenium. The resistivity at room temperature is 13.58 μ Ω· cm, and the ionization potential is 7.30 ± 3V. 1.1.2 Chemical Properties Tantalum has excellent chemical stability and does not react with air or water. It does not react with hydrochloric acid, concentrated nitric acid, or aqua regia under both cold and hot conditions. Except for hydrochloric acid, it can resist all inorganic acids, including aqua regia, as well as the erosion of any alkaline solution. Soaking tantalum in sulfuric acid at 200 ℃ for one year resulted in only 0.006 millimeters of surface damage. Experimental results have shown that tantalum does not react with alkaline solutions, chlorine gas, bromine water, dilute sulfuric acid, and many other agents at room temperature. It only reacts with hydrofluorine and hot concentrated sulfuric acid, which is rare in metals. Another important characteristic of it is its ability to absorb gases such as hydrogen, nitrogen, oxygen, etc., and form corresponding solid solutions or compounds.

Mechanical properties

Tantalum metal has a high melting point, strong corrosion resistance, and good strength. Tantalum is highly ductile and can be drawn into thin foils in a wire like manner. Its coefficient of thermal expansion is very small, expanding only 6.6% for every one degree Celsius increase. In addition, it has strong toughness and is even better than copper. However, the low hardness, insufficient scratch and deformation resistance, and short service life limit the promotion and application of tantalum metal. Therefore, strengthening the surface treatment is very important.

The characteristics of tantalum make its application fields very broad. Tantalum can be used as a substitute for graphite cathodes in equipment for producing various inorganic acids, and its lifespan can be increased by several tens of times compared to graphite cathodes. In addition, in industries such as chemical, electronic, and electrical industries, tantalum can replace the tasks previously undertaken by the precious metal platinum, greatly reducing the required costs.

Introduction and basic structure of tantalum capacitors

Solid tantalum capacitors are formed by pressing tantalum powder into shape and sintering it into an anode in a high-temperature furnace. The dielectric is activated by placing the anode in acid to form a porous amorphous Ta2O5 dielectric film. The working electrolyte is manganese nitrate solution, which is decomposed at high temperature to form MnO2, which is connected through a graphite layer.

Tantalum capacitors have superior performance, which can achieve larger capacity while making their volume relatively small and easy to process into small and chip shaped components. They are suitable for the current automation and miniaturization development of electronic device assembly and have been widely used. Tantalum capacitors have the main characteristics of long lifespan, high temperature resistance, high accuracy, but relatively weak voltage and current resistance, and are generally used in high-capacity filtering parts of circuits.

Process flow

1、 Process manufacturing process

The general process flow is as follows (key processes are highlighted in bold):

Raw Material Inspection - Forming Process - Sintering Process - Wet Inspection QC - Welding Process - Empowerment Process - Coating Process - Graphite Silver Paste Process - Silver Immersion QC - Assembly Process - Moulding Process - Sandblasting Process - Printing Process - Edge Cutting Process - Pre Testing Process - Experienced Process - Testing Process - Appearance Process - Ribbon Process - Check Plate Process - Finished Product QC - Warehousing Storage - Packaging - Shipping QC. Below is a brief introduction to the process route:

a) Raw material inspection:

b) Forming:

Mix tantalum powder particles with different proportions of thickness and binder dissolved in the solvent evenly, wait for the solvent to evaporate, and then press them together with tantalum wire to form anode tantalum blocks; This process has a high degree of automation. Every certain period of time, the operator pours the mixed tantalum powder into the feeding tray (to prevent the self weight generated by too much tantalum powder from sticking together), and the equipment automatically presses and forms according to the size of the mold cavity; c) Dewaxing and sintering:

Dewaxing, also known as pre firing, involves removing the binder from the pressed tantalum blocks; Sintering is the process of sintering tantalum blocks that have already been debonded into micro porous bodies with certain mechanical strength. The sintering process only involves the fusion of the parts in contact between particles. However, if the sintering temperature is too high, it can lead to excessive fusion between particles, resulting in a decrease in surface area; Dewaxing and sintering have strict control requirements for parameters such as vacuum degree, starting temperature, temperature rise, insulation, cooling, and discharge and converter time of the furnace.

d) Wet inspection QC:

Wet inspection is the process of determining the sintering specific capacity of tantalum blocks through sampling and electrical parameter testing after sintering, optimizing the parameters of the next sintering process (current density, formation voltage, etc.), and providing feedback to adjust the temperature control curve and other parameters of the previous sintering process. At the same time, the appearance size, strength and other parameters of tantalum blocks and tantalum wires will also be tested.