PCB News - Introduction to the world's copper foil technology for PCB

1. The development of the world's PCB copper foil production

In 1937, the Anaconda Copper Smelter in the United States began to establish a copper foil production industry. At that time, copper foil was only used for waterproofing of wooden roofs. In the early 1950s, due to the emergence of the printed circuit board industry, the copper foil industry became an important cutting-edge precision industry associated with the electronic information industry.

In 1955, the American company Yates separated from Anaconda and became the world's first company specializing in the production of electrolytic copper foil for PCBs. In 1957, the American Gould Company also invested in this industry, and evenly divided the Yates Company's exclusive market for PCB copper foil in the world. Since Japan’s Mitsui began to introduce American copper foil manufacturing technology in 1968, Japan’s Frukawa and Nippon Mining have cooperated with Yates and Gould respectively to make Japan’s copper foil industry There has been a big development.

In 1972, the US Yates company's patent for electrolytic copper foil production was published, marking the world's electrolytic copper foil manufacturing and surface treatment technology has entered a new stage. According to statistics, the world's production of electrolytic copper foil for PCBs reached about 180,000 tons in 1999. Among them, Japan is 50,000 tons, Taiwan is 43,000 tons, China is 19,000 tons, and South Korea is about 10,000 tons. It is predicted that the world's production of electrolytic copper foil will increase to 253,000 tons in 2001. Among them, the fastest growth rate is Japan (predicted to be 73,000 tons in 2001) and Taiwan (predicted to be 65 thousand 1).

Japan, which occupies the first place in the world's copper foil production and technology, has made rapid development in copper foil production and technology due to the development of printed circuit boards and copper clad laminates in recent years.

And in recent years, overseas manufacturers invested by Japan have been established in North America, China, Taiwan, Southeast Asia, Europe and other countries and regions. Major Japanese electrolytic copper foil manufacturers include: Mitsui Metal Mining Company, Japan Energy Company (formerly Nippon Mining Company), Furukawa Electric Company, Fukuda Metal Foil Industrial Company, Japan Electrolysis Company, etc. The characteristics of Japan's electrolytic copper foil production are: In recent years, it is developing towards more high-tech and cutting-edge products.

The output of electrolytic copper foil in Taiwan currently ranks second in the world. The main large-scale manufacturers are: Changchun Petrochemical Company, Taiwan Copper Foil Company, Nanya Plastic Company, etc.

2. High-performance electrolytic copper foil

In the world copper foil industry in recent years, some high-performance electrolytic copper foil manufacturing technologies have been continuously innovated and developed. An overseas copper foil market research expert recently believed that due to the future high-density thinning (LIS=0.10mm/0.10mm or more), multi-layer (6 layers or more), thinning (0.8mm) and high frequency A large number of high-performance copper foils will be used in PCB circuit boards, and the market share of this kind of copper foil will reach more than 40% in the near future. The main types and characteristics of these high-performance copper foils are as follows.

1. Excellent tensile strength and elongation of copper foil, excellent tensile strength and elongation of electrolytic copper foil, including both under normal conditions and high temperatures. Under normal conditions, high tensile strength and high elongation can improve the processability of electrolytic copper foil, enhance rigidity and avoid wrinkles to improve production qualification rate. High temperature extensibility (HTE) copper foil and high tensile strength copper foil at high temperature can improve the thermal stability of PCB and avoid deformation and warpage. At the same time, the problem of copper foil high temperature fracture (usually copper sinks are used in the inner layer of multilayer boards to make through-hole inner rings, which are prone to ring cracks during dip soldering). The use of HTE copper foil can be improved.

2. Low profile copper foil

The technological advancement of high-density wiring of multi-layer boards has made it possible to continue to use conventional electrolytic copper foil, which is no longer suitable for manufacturing high-precision PCB pattern circuits. In this case, a new generation of copper foil-low profile (LP) or ultra-low profile (VLP) electrolytic copper foil has appeared one after another. Low-profile copper foil was successfully developed in the United States (Gould's Arizona factory) and Japan (Mitsui Metal Company, Furukawa Electric Company, Fukuda Metal Industry Company) in the early 1990s (1992-1994), almost at the same time.

Generally, the original foil is made by electroplating, and the current density used is very high, so the microcrystals of the original foil are very rough, showing coarse columnar crystals. The "ridgelines" of the cross-faults of its slices have large undulations. The crystallization of LP copper foil is very fine (below 2μm), is equiaxed crystal grains, does not contain columnar crystals, it is lamellar crystals, and the ridges are flat. The surface roughness is low. VLP copper foil is actually measured and the average roughness (R.) is 0.55μm (generally copper foil is 1.40μm). The maximum roughness (Rm?x) is 5.04μm (the general copper foil is 12.50μm). Comparison of various copper foil characteristics

In addition to ensuring the general performance of ordinary copper cylinders, VLP and LP copper foils also have the following characteristics.

1. The initial precipitation of VLP and LP copper foil is a crystal layer keeping a certain distance. The crystals are not vertically connected and stacked up, but form a slightly concave and convex flat sheet. This crystalline structure can prevent the sliding between metal crystal grains, and has a relatively large force to resist the deformation caused by the influence of external conditions. Therefore, the tensile strength and elongation (normal state, hot state) of copper foil are better than general electrolytic copper foil.

2. LP copper foil is smoother and more delicate on the roughened surface than ordinary copper foil. At the interface between the copper foil and the substrate, there will be no residual copper powder (copper powder transfer phenomenon) after etching, which improves the surface resistance and interlayer resistance characteristics of the PCB, and improves the reliability of the dielectric performance.

3. It has high thermal stability and will not recrystallize copper due to multiple lamination on a thin substrate.

4. The time to etch the pattern circuit is less than that of normal electrolytic copper foil. Reduce the side erosion phenomenon. The white spots after etching are reduced. Suitable for the production of fine lines.

5. LP copper foil has high hardness, which improves the drillability of multilayer boards. It is also more suitable for laser drilling.

6. The surface of LP copper foil is relatively flat after the multilayer board is pressed and formed, which is suitable for the production of fine wire circuits.

7. The thickness of LP copper foil is uniform, the signal transmission delay is small after the PCB circuit board is made, the characteristic impedance is well controlled, and there is no noise between lines, layers and layers.

Low profile copper foil is very different from general electrolytic copper foil in terms of fine structure, such as grain size, distribution, crystal orientation and distribution. The low-profile copper foil manufacturing technology is based on the electrolyte formula, additives, electroplating conditions, etc. in the original traditional general electrolytic copper foil production, with great improvements and technological advances.