Effect of microcrystalline phosphor copper balls on electroplating
Sep 27, 2023
The microcrystalline phosphorus copper anode is a microcrystalline copper ball with a crystal structure that has undergone a microcrystallization process, which changes the crystal structure of the metal in a deeper level, improves the movement and diffusion capabilities of the grain molecules, and segregates at the grain boundaries. The element has diffused into the grains, eliminating grain boundaries to achieve homogenization, resulting in a more even distribution of phosphorus. With the development of electronic plating technology, circuit board manufacturers have increasingly stringent performance requirements for coatings. In addition to a wide variety of additives, the quality of phosphor copper anode plays a decisive role in improving the performance of the plating solution and the quality of electroplating. At present, microcrystalline phosphor copper anodes are gradually emerging in the Chinese industry.
1. The difference between microcrystalline phosphor bronze balls and ordinary phosphor bronze balls
The so-called microcrystalline phosphor copper balls in the industry are phosphor copper balls with an average grain size diameter of no more than 60 ¦Ìm. (Table 1 shows the measured dimensions of ordinary and microcrystalline phosphor copper anodes produced by a domestic manufacturer). In appearance, due to the different manufacturing process of microcrystalline phosphor copper balls, their crystal grains are tiny and their physical properties are better. Therefore, the surface quality of microcrystalline copper balls is better than ordinary copper balls, which is smoother and fuller, and there is no copper powder. Produced, while ordinary phosphor bronze balls will have a little copper powder on their surface. In terms of microstructure, through comparison of metallographic photos, it is found that the crystal grains of ordinary phosphor copper balls can be clearly seen when magnified 200 times, and the crystal grains are relatively coarse; there are obvious grain boundaries, and there is phosphorus enrichment at the micro level. Phosphorus appears uneven and slightly segregated. In actual electroplating applications, the grain boundaries are particularly easy to dissolve, and the thickness of the black film is not very uniform. Only when the microcrystalline phosphor copper ball is magnified 500 times can the crystal grains be vaguely seen. The crystal grains are extremely small, evenly distributed, and dense in structure. There are no grain boundaries; the elements segregated on the grain boundaries have diffused into the grains, and the distribution of phosphorus is more uniform.(Figure 1 (a) (b) is the measured metallographic structure diagram of ordinary and microcrystalline phosphor copper anodes produced by a domestic manufacturer) In terms of chemical composition, except for the slightly smaller phosphorus content of microcrystalline phosphor copper balls ( 0.025-0.050%), and there is no obvious difference in others (see Table 2). However, because the microcrystalline copper balls have fine grains and more uniform phosphorus distribution, conditions are met to control the phosphorus content to a lower range. Copper with a lower phosphorus content has better electrochemical performance, so the control range of the phosphorus content is lower. It is more beneficial to the quality of electroplating.
2. Comparison in PCB plating process
2.1 Large and small current electroplating experiments In the laboratory, the main setting times for large and small current experiments are 30 minutes and 120 minutes of electroplating. Look at the black film formed on the surface: the phosphorus does not fall off the surface of ordinary copper balls, so the film forms quickly. It takes 20 minutes to form a uniform and complete black film and the black film thickens later, but the black film is loose and easy to fall off. Check the hand feel and find that the black film on the copper ball is rough and contains fine granular copper slag; due to the manufacturing process, the microcrystalline copper ball has There is a little dephosphorization on the surface, and the film forms quickly. A very uniform, complete and thin black film is basically formed in 30 to 40 minutes. And the film formation is uniform, the film layer is thin, the bonding force is strong, and the black film feels delicate.Comparison found that although ordinary copper balls form the fastest film, the black film tissue they generate is loose and easy to fall off, which is more obvious under high current conditions. Microcrystalline copper balls can not only produce black films quickly, but also ensure black film formation. The film is complete, uniform in thickness and has strong bonding force. Faster film formation speed means less copper loss. Microcrystalline copper balls can adapt to both the production needs of small currents and the production of large currents due to rush for goods. In short, microcrystalline phosphor copper anode film formation is fast and good, and the efficiency and performance are significantly better than ordinary products [2].
2.2 The effect in actual production was inspected and observed from the electroplating production line. The black film formed by the microcrystalline phosphor copper anode in the titanium basket is thin and dense, and no excessive anode mud is found at the bottom of the anode bag; the copper ball is smooth in appearance and has no honeycomb bumps. Uneven rough surfaces dissolve into spherical and regular shapes. The black film generated after electrolysis is thin, continuous and dense. There are no tiny particles included in the hand check and the black film is not easy to fall off. On the other hand, when inspecting the titanium basket after being used for 3 months in production, it was found that the flow rate of the plating solution in the anode bag was fast, the pores of the anode bag were not blocked, and there was little black mud generated in the bag.The film of ordinary phosphor copper anode is thicker and easy to fall off. After long-term use, more black mud is formed. After electrolysis for a period of time, most of the surfaces have uneven rough surfaces and become irregular spherical shapes. Hand inspection shows obvious inclusion of tiny particles. Explained from the crystal structure: Microcrystalline phosphorus copper has no grain boundaries, and the film is thin, dense and strong. The small grain size naturally shows high bonding strength between the particles and the black film, and it is not easy to produce a copper ball structure.
