According to the different methods of making copper foil, it can be divided into calendered copper foil and electrolytic copper foil.
(1) Rolled Copper Foil
Rolled copper foil is the original foil made of copper plate after repeated rolling, and roughened according to the requirements. Due to the limitation of calendered copper foil processing technology, its width is difficult to meet the requirements of rigid copper clad laminate, so rolled copper foil is rarely used on rigid copper clad laminate. Because the bending resistance and elastic coefficient of rolled copper foil are higher than those of electrolytic copper foil, it is suitable for flexible copper clad laminate. Its copper purity (99.9%) is higher than that of electrolytic copper foil (99.8%), and its matte side is smoother than that of electrolytic copper foil. Therefore, in recent years, rolled copper foil is used in high-frequency & high-speed signal transmission and thin wire printed circuit board. It can also improve the effect of sound quality when it is used in PCB substrate of audio equipment. It is also used in the "metal sandwich board" made to reduce the coefficient of thermal expansion (CTE) of multilayer circuit boards with thin wires and multilayers. In recent years, Japan has also introduced new varieties of rolled copper foil, such as high toughness rolled copper foil, a kind of rolled copper foil with low temperature crystallization characteristics. Because of its high bending resistance, it is suitable for flexible plates. The other is the non oxygen rolled copper foil, which has the characteristics of oxygen content of only 0.001% and high tensile strength. It can be used in printed circuit boards with high lead strength in tab and printed boards of audio equipment.
(2) Electrolytic copper foil
Electrolytic copper foil is to dissolve copper into solution, and then electrodeposition copper sulfate electrolyte under the action of direct current in special electrolytic equipment to make the original foil, and then carry out a series of surface treatment such as heat-resistant layer treatment and anti-oxidation treatment. Electrolytic copper foil is different from rolled copper foil in that the crystal morphology on both sides of electrolytic copper foil is different. The one side close to the cathode roller is smooth, which is called shiny side; the other side presents concave convex crystal structure, which is rough, called matte side. The surface treatment of electrolytic copper foil and rolled copper foil is also different. As electrolytic copper foil is columnar crystal structure, its strength and toughness are inferior to that of rolled copper foil, so electrolytic copper foil is mostly used in the production of rigid copper clad laminate.
The technical performance requirements of electrolytic copper foil (including roughened foil) mainly include thickness, area weight, appearance, tensile strength, peel strength, anti-oxidization and mass resistance coefficient. In addition to the above 7 main performance requirements, manufacturers in some countries and regions also have other performance requirements, such as elongation, folding resistance, hardness, elastic coefficient, elongation @ high temperature, roughness, etching, solderability, adhesion of UV ink and color equivalence.
With the continuous development of high-density thin wire, multi-layer, thin (< 0.8mm) and high-frequency printed circuit board, some high-performance electrolytic copper foil manufacturing technology also came into being. It is estimated that the market share of this kind of copper foil will reach more than 40%. The types of these high performance electrolytic copper foils are as follows.
① Excellent tensile strength and elongation of copper foil.
The high tensile strength and high draft rate under normal conditions can improve the processability of electrolytic copper foil, enhance the rigidity and avoid wrinkles, so as to improve the qualified rate of production. High temperature extensibility copper foil and high tensile strength copper foil at high temperature can improve the thermal stability of printed circuit board and avoid deformation and warpage.
② Low profile copper foil
With the development of high density wiring technology of multilayer board, the traditional electrolytic copper foil can not meet the needs of manufacturing high-precision printed circuit board. Therefore, a new generation of copper foil, low profile (LP) and ultra-low profile (VLP) electrolytic copper foil have emerged. Compared with ordinary electrolytic copper foil, LP copper foil has fine crystal (< 2 / ZM), equiaxed grain, no columnar crystal, lamellar crystal, flat edge and low surface roughness. The surface roughness of VLP copper foil is lower, and the average roughness is 0.55 μ m (1.40 μ m for common copper foil). In addition, it has better dimensional stability and higher hardness.
③ Ultra thin copper foil
For portable electronic products, such as mobile phones and notebook computers, copper foil used in multilayer boards containing micro buried and blind link L and organic resin packaging substrates such as BGA and CSP are advancing to thin foil type and ultra-thin foil type. At the same time, it is necessary to use very thin copper foil in the substrate in order to process the micro wire hole of copper foil directly. In Japan, the United States and other countries, the electrolytic copper foil of 9μm, 5μm and 3μm can be industrialized. At present, the difficulty or key point of the production technology of ultra-thin copper foil is whether it can be directly produced without carrier, and the product qualification rate is high and the development of new carrier.