Introduction to the definition of copper foil:
Copper foil, also known as copper foil, is a type of negative electrolytic material that is a thin, continuous metal foil deposited on the substrate of a circuit board. It serves as the conductor of the PCB. It is easy to adhere to the insulation layer, accept printed protective layers, and form circuit patterns after corrosion. Copper mirror test: a corrosion test of soldering flux using a vacuum deposited thin film on a glass plate.
Copper foil: a negative electrolytic material, a thin, continuous metal foil deposited on the substrate layer of a circuit board, used as a PCB
Copper foil is a conductive material. It is easy to adhere to the insulation layer, accept printed protective layers, and form circuit patterns after corrosion. Copper mirror test: a corrosion test of soldering flux using a vacuum deposited thin film on a glass plate.
Copper foil, electrolytic copper foil is mainly used in digital cameras, mobile phones, DVDs, HVD precision electronic products, computer communications, and wires.
1) Appearance quality
Both sides of the copper foil must be free of scratches, dents, wrinkles, dust, oil, corrosive substances, fingerprints, pinholes and penetration points, as well as other defects that affect the lifespan, usability or appearance of the copper foil.
2) Mass per unit area
In general, when manufacturing printed circuit boards, under the same manufacturing process conditions, the thinner the copper foil thickness, the higher the precision of the produced circuit. However, as the thickness of copper foil decreases, the quality of copper foil becomes more difficult to control, and the production process requirements for copper foil become higher. Generally, the outer layer of double-sided printed circuit boards and multilayer boards uses copper foil with a thickness of 0.035mm, while the inner layer of multilayer boards uses copper foil with a thickness of 0.018mm. 0.070mm copper foil is commonly used for power layer circuits in multi-layer boards. With the continuous improvement of electronic technology, the precision requirements for printed circuits are becoming increasingly high. Nowadays, 0.012mm copper foil is widely used, and 0.009mm and 0.005mm carrier copper foils are also being used.
3) The peel strength is an important characteristic of copper foil in the manufacturing of printed circuit boards, which is clearly required in copper foil standards. However, there is no clear requirement for peel strength, whether it is IEC, IPC, JIS or GB/T5230, only stipulating that peel strength should comply with the procurement documents or be agreed upon by both the supply and demand parties. For electrolytic copper foil used in PCB, the most important performance is peel strength. The copper foil is pressed onto the outer surface of the copper-clad laminate. If the peel strength is poor, the etched copper foil lines may easily detach from the surface of the insulating substrate material. In order to enhance the bonding strength between copper foil and substrate, it is necessary to roughen the surface of the raw foil (the bonding surface with the substrate) to form firm nodular and dendritic crystals on the surface with a high degree of roughness, achieving a high specific surface area, strengthening the adhesion and embedding force of resin (resin on the substrate or copper foil adhesive resin) infiltration, and increasing the chemical affinity between copper and resin.
Generally, electrolytic copper foil is used for the outer layer of printed circuit boards, and the peel strength needs to be greater than 1.34kg/cm.
4) Since the 1990s, due to the development of printed circuit technology, it has been required that the copper-clad laminates used to form printed circuit boards must be able to withstand higher temperatures and longer heat treatments than in the past. Higher requirements have been put forward for the thermal oxidation discoloration resistance of the copper foil surface, especially for the welding surface (copper foil smooth surface).
In addition to the above four main performance requirements, there are strict requirements for the electrical properties, mechanical properties, weldability, copper content, etc. of copper foil. Please refer to IPC-4562 "Standard for Metal Foil for Printed Circuit" for details.
There is currently no unified national or industry standard for electrolytic copper foil used in 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 been constantly improving with the rapid development of electronic products. The increasing miniaturization of electronic devices, the continuous development of surface mount technology for printed circuits, and the continuous growth of multi-layer printed circuit board production have led to the development of printed circuits towards refinement, high reliability, high stability, and high functionality. As a result, higher requirements have been put forward for the performance and variety of electrolytic copper foil, leading to a new development trend in electrolytic copper foil technology. High performance electrolytic copper foil with fewer defects, fine grains, low surface roughness, high strength, high ductility, and thinner thickness will be widely used in high-end, multi-layer, thin, and high-density printed circuit boards. It is estimated that its market application proportion will reach more than 40%.
① Excellent tensile strength and elongation copper foil. Under normal conditions, high tensile strength and elongation can improve the processing characteristics of electrolytic copper foil, enhance rigidity, avoid wrinkles, and improve production yield. High temperature extensibility (THE) copper foil and high tensile strength copper foil at high temperatures can improve the thermal stability of printed boards, avoiding deformation and warping.
② Low profile copper foil. The advancement of high-density wiring technology in multi-layer boards has made traditional electrolytic copper foils unsuitable for the production of high-precision printed circuit board graphics circuits. Therefore, a new generation of copper foils, low profile (LP) and ultra-low profile (VLP) electrolytic copper foils, have emerged successively. A low profile copper foil with a roughness of less than 1/2 of that of a general roughened copper foil, and an ultra-low profile copper foil with a roughness of less than 1/3 of that of a general roughened copper foil. The crystallization of low profile copper foil is very delicate, with equiaxed grains and no columnar crystals. It is a layered crystal with flat edges and low surface roughness. Generally, it has both high temperature, high elongation, and high tensile strength. Ultra low profile copper foil (VLP) has a lower surface roughness, with an average roughness of 0.55 μ m (usually 1.40 μ mm for copper foil), and also has better dimensional stability and higher hardness.

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