1. Appearance quality
Both sides of the copper foil shall be free of scratches, pits, wrinkles, dust, oil, corrosives, fingerprints, pinholes, penetration points and other defects that affect the 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 is, the higher the precision of the circuit is. However, as the thickness of copper foil decreases, the quality of copper foil is more difficult to control, and the production process requirements for copper foil are higher. Generally, 0.035mm copper foil is used for the outer layer of double-sided printed circuit board and multilayer board, and 0.018mm copper foil is used for the inner layer of multilayer board. 0.070mm copper foil is mostly used for power layer circuit of multilayer board. With the continuous improvement of the level of electronic technology, the requirements for the accuracy of the printed circuit are getting higher and higher. Now 0.012mm copper foil has been widely used, and 0.009mm and 0.005mm carrier copper foil are also being used.
3. Peel strength
When manufacturing printed circuit boards, the important characteristics of copper foil are clearly required in copper foil standards. However, there is no clear requirement for peel strength, whether in IEC, IPC, JIS or GB/T5230, only that the peel strength should comply with the provisions of the procurement documents or be agreed by the supplier and the demander. For PCB Electrolytic copper foil Peel strength is the most important of all properties. The copper foil is pressed on the outer surface of the copper clad plate. If the peel strength is poor, the copper foil lines formed by etching may be easily detached from the surface of the insulating substrate material. In order to make the copper foil have a stronger bonding force with the base material, the rough surface of the raw foil (the bonding surface with the base material) needs to be roughened to form a firm nodular and dendritic crystal on the surface and a rough surface with a high degree of expansion to achieve a high specific surface area, and strengthen the adhesion and embedding force of the resin (resin on the base material or copper foil adhesive resin), It can also increase the chemical affinity between copper and resin.
Generally, electrolytic copper foil is used for the outer layer of printed circuit board, and the peel strength needs to be greater than 1.34kg/cm.
4. Oxidation resistance
Since the 1990s, due to the development of printed circuit technology, it is required that copper clad laminates forming printed circuit boards must be able to withstand higher temperatures and longer heat treatments than in the past. Higher requirements are put forward for the thermal oxidation discoloration resistance of 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, solderability, copper content, etc. of copper foil.
