Analyze and compare the influence of electrochemical and electroless palladium passivation methods on the discoloration of microwave silver coating

Passive intermodulation is an important factor that affects the capacity of wireless communication systems, and silver-plated products will cause the performance of passive intermodulation products to decline or even fail due to the oxidation and discoloration of the silver-plated layer. It is necessary to improve the surface quality of silver-plated products.

This article mainly uses electrochemical passivation technology and electroless plating palladium technology to post-process microwave silver-plated products, and compares the resistance of the two processes with the traditional chemical passivation process. Corrosion performance.

1 Experimental method

1. Experimental materials and equipment

This experiment mainly uses copper-based silver-plated specimens, and the chemical reagents are: Ce(NO3)3/H2O2, H2O2, NH3·H2O, PdC12.

The main instruments and equipment are: constant temperature water bath, salt spray box, electrochemical workstation, scanning electron microscope.

2. Process flow

Electrochemical passivation process: prepare Ce(NO3)3/H2O2 passivation solution with a concentration of 0.05mol/L and heat it to (40±1)℃. Using the titanium plate as the anode and the silver-plated test piece as the cathode, passivate for 7 minutes at a current density of 0.8 mA/cm2, rinse with deionized water after taking it out, and dry it with cold air.

Electroless palladium plating passivation process: the surface of the silver-plated test piece is polished and cleaned and placed in a treatment solution composed of palladium source, complexing agent and reducing agent, passivated at 40°C for 1 h, and then taken out. Rinse with deionized water and dry with cold air.

3. Performance test

The SSX-5500 scanning electron microscope was used to observe the surface morphology of the passivation film of the silver-plated layer.

Place the silver-plated test piece in a neutral salt spray test box at a temperature of (35±1)℃, take out the silver-plated test piece after 120h, dry it naturally for 1h, clean it with warm water, and dry it with cold air, in accordance with industry standards Evaluate the corrosion rate.

Using electrochemical workstation to measure the Tafel curve of the specimen, the starting potential of the test is controlled to be about 250mV below the corrosion potential of the specimen, the polarization direction of forward polarization is adopted, and the scanning speed is set to be about 0.66mV/s .

2 Results and discussion

The surface morphology of the passivation film of the two processes is shown in Figure 1. The film obtained by electrochemical passivation is thicker, and uniform and dense oxide ball particles are formed on the surface; the surface of the silver-plated layer obtained by electroless palladium passivation shows a clearer bright black, and the passivation film is dense but thin.

Figure 2 shows the corrosion rates of the silver-plated passivation layer of different processes. The corrosion rates of blank specimens, electrochemical passivation specimens, and electroless palladium passivation specimens are 58.7%, 1.8%, and 2.7%, respectively.

3 Conclusions

The distribution of the electrochemical passivation film is relatively more uniform and dense than the electroless palladium passivation, and the thickness of the passivation film is also higher.

Corrosion pits appear after the blank test piece is placed in the salt spray box for 24 hours. The electroless palladium passivation test piece and the electrochemical passivation test piece are 96 and 120h respectively. The silver plated test piece obtained by electrochemical passivation is resistant The corrosive effect is the best.

After passivation, the corrosion potential value of the electroless palladium plating passivation process, electrochemical treatment process, and blank sample decreases in sequence, and the corrosion current value increases in sequence. The corrosion resistance of the passivation film obtained by electrochemical passivation The performance is better than the corrosion resistance of the passivation film and the blank specimen obtained by the electroless palladium passivation process.