Diamond Micro Powder Electroless Nickel Plating Technology

Traditional diamond powder coating is difficult to achieve the integrity of the nickel layer, the thickness of the nickel layer is uneven, and the adhesion between diamond particles cannot be avoided, and the diamond powder is mixed during and after the diamond powder coating process. A large number of nickel powder, diamond powder electroless nickel plating process, on the basis of traditional process, optimize the pretreatment process, adopt mature high-phosphorus electroless nickel plating process, realize multi-cycle nickel plating, and greatly improve the plating quality. Under the circumstance, the cost of plating is reduced, and the waste of nickel plating solution is reduced.

Diamond powder electroless nickel plating is a very early practical process technology. It was called diamond metallization in the early days. At that time, diamond plating was mainly used for composite plating of diamond tools and diamond grinding wheels to enhance diamond and tools holding force of a specific substrate (we call it binding force). The current common process basically follows the traditional process (oil removal - roughening - sensitization - palladium activation - electroless nickel plating).

Since 2015, with the large-scale promotion and application of diamond wire saws in the photovoltaic industry to replace traditional mortar + steel wire cutting silicon materials, diamond wire saws, as a relatively uncommon product, suddenly became popular. The great development of the wire rod continuous plating industry, as the main material of diamond wire saw - diamond micropowder, diamond micropowder electroless nickel plating is also accompanied by this tuyere, and has become a rapidly developing process technology in recent years.

Diamond and diamond powder abrasive: The diamond mentioned here is synthetic diamond crystal, which is artificially produced by graphite and catalyst in the mold of the six-sided top press under high temperature and high pressure. Physical and chemical properties, it is currently the material with the highest hardness, and is often used in the production of high-hardness tools and abrasives. After crushing, particle size sorting, shape classification and grading, artificial diamond crystals are used as diamond fine powder with determined specifications and are applied to diamond wire saws. (5-10, 8-12, 10-20, 20-30, 30-40, 40-50, in microns), follow the pattern of using large-diameter diamonds for thick lines and small-diameter diamonds for fine lines, 2019 In May of this year, the diamond wire saw industry held an annual industry conference in Nanjing. The report at the meeting showed that the minimum diameter of the diamond wire saw busbar for large-scale production has reached 50 microns (5 wires), which is used for silicon material cutting and used for The minimum busbar diameter of the diamond wire saw for rare earth permanent magnet cutting is 120 microns (12 wires).

1. Pretreatment process solution and parameters of diamond micropowder

Degreasing: The commercialized alkaline degreasing powder is used, and the degreasing powder is required to contain a surfactant, which has the ability to emulsify and saponify the oil. The general concentration is 50-100 g/L, and the temperature is 50°C;
Coarsening: use dilute nitric acid (5%) and dilute hydrochloric acid (1%), use at room temperature, and have the ability to dissolve catalyst metals such as iron, nickel, cobalt, and chromium, at room temperature;
Sensitization: use stannous chloride (20 g/L) + hydrochloric acid (50 mL/L) to prepare a sensitizing solution at room temperature;
Palladium activation: use palladium chloride (0.1 g/L) + hydrochloric acid (15 mL/L) to prepare a palladium activation solution, at room temperature;
Palladium reducing solution: adopt commodity "palladium reducing agent", 50% dilution is used, and palladium reduction process temperature is 65 ℃;
Each of the above processes requires stirring to make the diamond micro powder particles fully contact and react with the solution. The reaction process requires a corresponding time, and then fully settle, recover the solution, and wash it with pure water.

2. Description of the pretreatment process

(1) Diamond micropowder is powder, and the processing process of the powder in the liquid is in the form of mortar, which always needs to go through: 1. Stirring the reaction between the powder and the solution, 2. Standing and settling, 3. Recovering the supernatant solution, 4. , Washing with pure water + stirring, 5. Settling by standing, 6. Discarding the supernatant waste water; repeat the process 4-6 for a total of 4 times.
(2) The powder cannot be completely separated from the solution. Therefore, for each washing with pure water, about 8% of the residual liquid will be absorbed by the powder and cannot be completely discarded. After 4 times of washing with pure water, it is basically 8%. The 4th power of the solution is diluted, that is, the dilution reaches 4.096*10-5. The quantitative method for checking whether it is cleaned is to use a conductivity meter of pure water to check the purity of the water after the last pure water washing, which is below 20PPM, that is, It is believed that cleaning this link will not cause pollution to the next link.
(3) The diamond micropowder degreasing and roughening process, when used in conjunction with an ultrasonic cleaner, is conducive to improving the efficiency of degreasing and coarsening of diamond micropowder, saving time in the process of degreasing and coarsening, and ensuring the effect of degreasing and swearing. , to improve the bonding force of diamond powder and coating. Ultrasonic cleaning cannot be applied in the sensitization and subsequent steps, because the film layer covering the powder particles has been formed in each step after sensitization, and the application of ultrasonic waves will destroy the just-made film layer.
(4) The whole process statement: 1. Degreasing + 4 times of washing; 2. Roughening + 4 times of washing; 3. Sensitization + 4 times of washing; 4. Palladium activation + 4 times of washing; 5. Palladium Reduction + 1 times of pure water washing; after the reaction of the palladium reducing solution, only one water washing is required, firstly, the activity of palladium can be maintained, and secondly, the palladium reducing agent is not a contaminant of the electroless nickel plating solution.

3. Conclusion

By optimizing the palladium activation and palladium reduction process parameters, the surface of the diamond micropowder particles in the low-concentration ionic palladium solution is fully activated, and there is no nickel powder in the nickel plating process.
By using a dispersant and maintaining a reasonable nickel plating rate, the diamond micropowder particles are independent without agglomeration and the nickel plating layer is uniform and complete.
Through the use of mature electroless nickel plating process materials, the multi-cycle stable operation of the diamond powder electroless nickel plating solution is realized, and the low emission and high benefit are realized.
By adopting the metering pump replenishment method, the solution replenishment speed is controlled, and the precise control of the reaction speed of diamond micropowder electroless nickel plating is realized.