In the electronic paste preparation technology, the preparation of the conductive phase metal powder is the key. For the conductor paste, the conductive phase is mostly composed of noble metal powders such as platinum, palladium, gold and silver, and the silver conductor paste is the most widely used. In recent years, due to the soaring price of precious metals, the cost of pulp has increased; in addition, the migration of silver is a defect of the silver paste itself, which cannot meet the requirements of high-performance electronic components. Therefore, it has become a development trend to reduce the cost, find a new type of conductive powder with excellent performance, and replace the precious metal with a base metal to prepare electronic paste. Under this background, the research of this subject is proposed. In this paper, the silver-coated copper powder was prepared by the replacement technology of the invention patent technology. The thermodynamics of the silver plating process was analyzed and calculated. The silver plating process and the silver plating structure were optimized. The silver-coated copper powder was used as the conductive phase to prepare the polymer. Silver-coated copper powder conductor paste; the performance of silver-coated copper powder slurry was studied, and the silver migration resistance of silver-coated copper powder slurry was discussed; and the industrialization was realized by the research technology of this paper. The main results obtained in this paper are as follows:
Through the analysis and calculation of the potential-pH diagram of Cu-Ag-NH3-H20 system and the thermodynamic analysis of the silver plating process, the theoretical basis for the preparation of silver-coated copper powder is provided.
(1) In the solution in the presence of NH3, the stable regions of Cu and Ag oxides are reduced, and the stable region of the water-soluble substances of Cu and Ag in the solution is greatly broadened, thereby improving the stability of the solution, so the preparation of the silver-coated copper powder is contained. It is preferred to use an aqueous solution of NH3.
(2) In the aqueous ammonia solution, the potential difference between copper and silver increases, and the thermodynamic tendency of the reaction increases, which is more favorable for the redox reaction under alkaline conditions.
(3) In the displacement-reduction reaction, a reducing agent must be added to obtain a silver-coated copper powder having a certain thickness of silver plating.
2. The silver-coated copper powder is prepared by the replacement patent-replacement method of the invention patent technology. The effect of the dispersibility of flake copper powder in aqueous solution, the composition of silver plating solution and the process conditions on the coating effect and performance of silver-coated copper powder, the appearance color, loose density and compaction resistance of silver-coated copper powder. Characterization of surface morphology, optimized composition and process conditions of silver-coated copper powder plating solution: AgNO3: 2.4～14.2g/L, ammonia water: 0.8g/L, formaldehyde: 1-3g/L, hydrazine hydrate: 1～ 4 g/L, composite dispersant: 1.0 g/L, pH: 11, bath temperature: 60 ° C, solid-liquid ratio: 1:15 to 1:20, stirring speed: 1000 r/min, silver-coated copper powder Drying: 50 ° C, 30 min. The silver-coated copper powder with different silver content was prepared by using silver-coated copper powder as the preferred bath composition and process conditions. The appearance color, compaction resistance, surface morphology, specific surface area and oxidation resistance were characterized. The variation of the performance of the silver-coated copper powder before and after silver plating obtained the following conclusions.
(1) The shape, bulk density and tap density of the silver-coated copper powder are mainly determined by the properties of the raw material copper powder, and the silver plating layer has little effect on the above properties.
(2) The silver plating layer has a certain influence on the particle size distribution of the silver-coated copper powder. The particle size D50 of the chip-shaped silver-coated copper powder decreases with the increase of the silver content. When the silver content is greater than 20%, the D50 starts to become larger.
(3) The silver plating has a great influence on the compaction resistance of the copper-coated copper powder, and the compaction resistance decreases with the increase of the coated silver content; when the coated silver content is greater than 20%, the reduction of the compaction resistance gradually becomes slower. And tend to be stable.
(4) The influence of silver plating on the specific surface area of the copper-coated copper powder is: when the silver content of the silver-coated copper powder is low, the specific surface area increases with the increase of the silver content; after the coated Ag content is more than 5%, the specific surface area is included. The silver content increases and decreases.
(5) The silver-coated copper powder is placed in the air, and the compaction resistance is increased. Compared with the amount of coated silver, the low silver content changes more than the high silver content. From the time comparison, the change in the first 6 days is larger, the change rate of the resistance of the silver-coated copper powder is greater than 10%, and the change rate of the resistance of the silver-coated copper powder is less than 10% after the silver content is greater than 20%; after 27 days, the copper-coated copper powder The rate of change in resistance tends to be stable.
(6) The amount of silver coated with silver-coated copper powder is different, and the oxidation temperature is different. The initial oxidation temperature of the low silver content is lower than the high silver content.
(7) The coating of silver-coated copper powder is analyzed by XRD as metallic silver and copper, and no oxides and other elements are present.
(8) The ideal deposition method of anti-oxidation silver coating is as follows: silver is deposited on the surface of copper powder in the form of flakes, and the sheets are lapped with each other, dense and non-porous, completely covering the flake copper powder and is isolated from the outside world. .
(9) The silver-coated copper powder is treated by wet ball milling. Under the same silver content, the coated copper-coated copper powder has a larger coating area on the base copper powder, and the silver plating layer is more tightly combined with the copper powder. After the silver-coated copper powder, the antioxidant capacity is improved.
4. Using silver-coated copper powder as the conductive phase, the viscosity, thixotropy, adhesion, square resistance, flexural strength and oxidation resistance of different organic carriers and different proportions of the slurry are compared and analyzed, and optimized. The organic carrier and the polymer silver-coated copper powder slurry are preferably formulated, and the properties are tested, and the following results are obtained:
(1) The organic carrier optimization system is an organic carrier prepared by combining polyester and polyacrylate by weight ratio of 1:1; ethylene glycol etherate as a solvent and a polymer content of 10% by weight.
(2) The preferred formula of the polymer silver-coated copper powder slurry is: silver-coated copper powder (silver content 30%), conductive phase content 55%, organic carrier content 45%.
(3) The silver content of the conductive phase in the silver paste is between 50% and 55%. The printing performance of the slurry is better. The content of the conductive phase silver-coated copper powder in the silver-coated copper powder slurry is between 55% and 60%. The printing performance of the material is better;
(4) The properties of the slurry prepared under the respective preferred formulations are: the silver paste square resistance is 12.8mΩ/□, the fold resistance change rate is 4%, the adhesion is qualified, and the stability is good; the silver-coated copper powder slurry The resistance is 14.6mΩ/□, the rate of change of the folded resistance is 5.5%, the adhesion is qualified, and the stability is good.
5. The experimental electrode was prepared by using silver paste and silver-coated copper powder slurry, and the silver migration phenomenon of different conductive phase, content, pattern shape, line spacing, etc. was observed by the water drop method experiment; the Tafel curve was performed on the experimental electrode. AC impedance curve test; the silver migration properties of silver-coated copper powder paste electrodes with different silver contents were studied, and the following conclusions were obtained:
(1) The main feature of the migration phenomenon in the water droplet experiment is that after the external voltage is applied, the electrode in the aqueous solution will undergo ion migration; the dendritic deposit is always generated on the cathode and grows toward the anode; the dendritic deposit is not a When electricity is started to grow, different conductive phases, different shapes of electrodes, and different applied voltages will affect the migration speed; the whole migration process is accompanied by the production of flocculent precipitates.
(2) The results of the Tafel curve and the AC impedance curve of the silver paste electrode and the silver-coated copper powder slurry electrode show that the silver-coated copper paste electrode moves in the positive direction from the self-corrosion potential of the silver paste electrode, and the self-corrosion current Lower, good corrosion resistance, slower electrode dissolution; silver-coated copper paste electrode in the electrolyte solution is better than silver paste electrode; silver paste electrode is more susceptible to corrosion, silver-coated copper paste The corrosion resistance of the electrode is better than that of the silver paste electrode, and the dissolution of the silver-coated copper paste electrode is slower than that of the silver paste electrode.
(3) The anti-migration mechanism of silver-coated copper powder is: the presence of copper inhibits the dissolution of silver in the silver-coated copper powder anode, and the concentration of silver ions decreases, which makes the sedimentation rate and dendritic growth slow down on the cathode, and improves its anti-migration. ability.
(4) The migration resistance of silver paste prepared by silver-coated copper powder is much stronger than that of silver paste; it is found that the silver migration resistance of silver-coated copper powder slurry is not enhanced with the increase of silver content in silver-coated copper powder. However, there is a suitable silver-containing range. When the silver-coated copper powder contains about 25% silver, the silver-coated copper powder slurry has the best silver migration resistance.
(5) For the first time, the relationship between the silver migration resistance of silver-coated copper powder and the structure of silver-plated layer was revealed. When the silver-coated copper powder coating structure is a mesh, the migration resistance against silver is better than that of the dense structure.