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1.4.2 Basic requirements for electrolytic copper foil
1) Appearance quality
There shall be no scratches, pits, wrinkles, dust, oil stains, corrosive substances, fingerprints, pinholes and penetration points on both sides of the copper foil and other defects that affect the service life, usability or appearance of the copper foil.
2) Mass per unit area
When manufacturing printed circuit boards, generally speaking, under the same manufacturing process, the thinner the copper foil, the higher the accuracy of the circuit. However, with the decrease of copper foil thickness, the quality of copper foil is more difficult to control, and the requirements for copper foil production technology are higher. Generally, 0.035mm thick copper foil is used for the outer circuit of double-sided printed circuit boards and multilayer boards, and 0.0 18mm thick copper foil is used for the inner circuit of multilayer boards. 0.070mm copper foil is mostly used in the power layer circuit of multilayer board. With the continuous progress of electronic technology, the accuracy of printed circuits is increasingly demanding. At present, 0.0 12mm copper foil is widely used, and 0.009mm and 0.005mm carrier copper foil are also used.
3) Peel strength
When manufacturing printed circuit boards, the important characteristics of copper foil are clearly required in the copper foil standard. However, there is no clear requirement for peel strength in IEC, IPC, JIS or GB/T5230. It is only stipulated that the peel strength should meet the requirements of procurement documents or agreed by both parties. For electrolytic copper foil for PCB, peeling strength is the most important of all properties. The copper foil is pressed on the outer surface of the copper clad laminate. If the peeling strength is poor, the etched copper foil wire may be easily separated from the surface of the insulating substrate material. In order to make the copper foil have stronger bonding force with the substrate, it is necessary to roughen the rough surface of the green foil (the bonding surface with the substrate) to form a solid rough surface with nodular and dendritic crystals and high spreading, so as to reach a high specific surface area, enhance the adhesion and embedding force of resin (resin on the substrate or copper foil bonding resin) and increase the chemical affinity between copper and resin.
Generally, the peeling strength of electrolytic copper foil for the outer layer of printed circuit board needs to be greater than 1.34kg/cm.
4) Oxidation resistance
Since 1990s, due to the development of printed circuit technology, it is required that the copper clad laminate forming the printed circuit board must be able to withstand higher temperature and longer heat treatment than in the past. Higher requirements are put forward for the thermal oxidation discoloration resistance of copper foil surface, especially for the welding surface (glossy surface of copper foil).
In addition to the above four main performance requirements, there are strict requirements on the electrical properties, mechanical properties, solderability and copper content of copper foil. See IPC-4562 Metal Foil Standard for Printed Circuits for details.
At present, there is no unified national standard or industry standard for electrolytic copper foil for lithium ion batteries.
1.4.3 development trend of electrolytic copper foil
The development of electrolytic copper foil has always followed the development of PCB technology, and PCB has also made continuous progress with the rapid development of electronic products. The miniaturization of electronic devices, the continuous development of surface mount technology of printed circuit and the continuous increase of the output of multilayer printed circuit board have promoted the development of printed circuit in the direction of miniaturization, high reliability, high stability and high functionality, put forward newer and higher requirements for the performance and variety of electrolytic copper foil, and made electrolytic copper foil technology have a brand-new development trend. High-performance electrolytic copper foil with few defects, fine grains, low surface roughness, high strength, good ductility and thin thickness will be widely used in high-grade, multilayer, thin and high-density printed circuit boards, and its market application ratio is expected to reach more than 40%.
① Copper foil with excellent tensile strength and elongation. Under normal circumstances, high tensile strength and high elongation can improve the processing characteristics of electrolytic copper foil, enhance rigidity and avoid wrinkling, thus improving the production qualification rate. Copper foil with high ductility and high tensile strength at high temperature can improve the thermal stability of PCB and avoid deformation and warping.
② Low profile copper foil. With the development of multilayer high-density wiring technology, the traditional electrolytic copper foil can no longer meet the needs of manufacturing high-precision and fine printed circuit boards. Therefore, a new generation of copper foil-low profile (LP) and ultra-low profile (VLP) electrolytic copper foil appeared one after another. Low-profile copper foil with surface roughness lower than that of general roughened copper foil 1/2, and ultra-low profile copper foil with surface roughness lower than that of general roughened copper foil 1/3. Low-profile copper foil has fine crystals, equiaxed, columnar-free, layered, flat edges and low surface roughness, and generally has high high-temperature elongation and high tensile strength. Ultra-low profile copper foil (VLP) has low surface roughness, with an average roughness of 0.55μm (1.40 μm for copper foil in general), and has better dimensional stability and higher hardness.