Classification of copper foil

Copper-clad laminate (CCL) and copper foil for printed circuit boards (PCB)

• CCL and PCB are the most widely used fields of copper foil, copper foil was first impregnated with resin bonding sheet hot pressing made of copper-clad laminate, which is used to make printed circuit boards, PCB has now become the majority of electronic products to achieve the circuit interconnection of the main components indispensable. The copper foil has now become a key material for PCBs that play a role in supporting and interconnecting components in electronic machine products. Since the 1990s, the development of IT product technology has promoted the development of PCB in the direction of multilayer, thin, high density, and high speed, which also requires copper foil with high performance, high quality, and high reliability to enter a new era of technology development. It also requires copper foil with high performance, high quality, and high reliability in the new era of technology development. At present, the majority of applications in the CCL and PCB industries are electrolytic copper foil.

Copper foil for lithium-ion secondary batteries

• According to the working principle and structural design of lithium-ion batteries, anode materials such as graphite and petroleum coke need to be coated on the conductive collector fluid. Copper foil has become the first choice of anode collector for lithium-ion batteries due to its good conductivity, soft texture, mature manufacturing technology, and relatively low price. Copper foil in the lithium-ion battery is both the carrier of the anode active material, but also as the anode electron collection and transmission conductor. In the early development of lithium-ion batteries, the copper foil used as an anode electrode collector was mostly called copper foil. However, due to the high price of calendered copper foil for lithium-ion batteries and the poor operability of the anode electrode coated with active material in the manufacturing process such as drying and rolling, it is easy to produce wrinkles and even fractures. At the same time, the manufacturing process of calendered copper foil is complicated, the process is long, and the production efficiency is low. In recent years, with the improvement of physical, chemical, mechanical, and metallurgical properties of electrolytic copper foil, as well as the advantages of easy production operation, high productivity, and relatively low price, the use of high-performance electrolytic copper foil instead of calendered copper foil has been applied in the actual production of lithium-ion batteries. At present, most lithium-ion battery manufacturers use electrolytic copper foil for the production of battery anode collectors.

Copper foil for electromagnetic shielding

• It is mainly used in hospitals, communication, the military, and other fields that need electromagnetic shielding. Due to the width limitation of calendered copper foil, electromagnetic shielding copper foil is mostly electrolytic copper foil.

Calendered copper foil

• This copper foil is made by melting and processing copper into copper sheets, which are then repeatedly rolled and tied to make the original foil, and then the original foil is subjected to a series of surface treatments such as roughening treatment, heat treatment, and anti-oxidation treatment according to requirements. The width of calendered copper foil is difficult to meet the production requirements of rigid CCL and lithium-ion battery anion sheets due to the limitations of the processing process. However, the calendered copper foil has a lamellar crystalline structure, so it has better strength and toughness than electrolytic copper foil. Therefore, calendered copper foil is mostly used for flexible printed circuit boards. In addition, because of the high density of calendered copper foil, the surface is relatively smooth, which is conducive to the rapid transmission of signals after making printed circuit boards, so some calendered copper foil is also used in high-frequency and high-speed transmission, a fine line printed circuit boards.

Electrolytic copper foil

• This copper foil is made by dissolving copper into copper sulfate electrolyte and then electrodepositing the copper sulfate electrolyte in special electrolytic equipment under the action of direct current to make the original foil. The foil is then subjected to a series of surface treatments such as roughening treatment, heat treatment, and anti-oxidation treatment according to requirements. The electrolytic copper foil differs from the calendered copper foil in that the two sides of the original electrolytic foil have different crystalline forms, with the side close to the cathode roller being smooth and becoming glossy. The other side has a convex and concave crystalline structure, which is rougher and becomes a rough surface. The surface treatment of electrolytic copper foil is also somewhat different from that of calendered copper foil. Since electrolytic copper foil is a columnar crystalline structure, it is less strong and tough than calendered copper foil. Electrolytic copper foil is now mostly used in the production of rigid copper-clad laminates and lithium-ion secondary battery anion carriers.

Single Surface Treated Copper Foil

• Among the electrolytic copper foils, the most produced variety is the single-sided surface-treated copper foil, which is not only the most used type of electrolytic copper foil in the manufacture of copper-clad and multilayer boards but also the copper foil with the largest application range. In the mid-1990s, another type of low-profile copper foil (LP) emerged among such products.

Double-sided (reversed-phase) processed copper foil

• Mainly used for fine lines of multilayer circuit boards, its glossy surface has a low profile, and this surface is laminated with the substrate to make a copper-clad board that can maintain a high precision line after etching. The demand for this type of copper foil is increasing.

The copper foil for CCL and PCB is classified according to its performance: standard copper foil, high temperature, and high extensibility copper foil, high extensibility copper foil, transfer resistant copper foil, low profile copper foil, etc.

Standard copper foil

• It is mainly used for pressing paper-based phenolic resin copper-clad laminate and epoxy resin glass fiber cloth copper-clad laminate. For copper foil used for paper-based copper-clad laminate, in order to improve the bonding strength of copper foil and substrate, after roughing treatment of copper foil, a layer of special adhesive is also applied, the roughness of this copper foil is relatively large, the thickness of the copper foil is generally around 35-70um, and various performance requirements are not very high. For the copper foil used for glass fiber cloth copper clad board, in addition to the necessary roughening treatment, but also heat-resistant treatment (such as galvanization, brass plating, etc.), special high-temperature resistant anti-oxidation treatment, and the base material has a high bonding force, the heat-resistant temperature of about 200 ℃, it is 18um copper foil as the main body.

High temperature and high extensibility copper foil (THE copper foil)

• It is mainly used for multilayer printing boards. Since the heat of multilayer printing boards will cause the recrystallization of copper foil when pressed together, it is necessary to have the same high elongation rate at high temperature (180℃) as at room temperature, so high-temperature elongation copper foil is needed to ensure that the cracking ring phenomenon does not occur during the production of printing boards.

High elongation copper foil (HD)

• Mainly used for flexible circuit boards, it requires high folding resistance, thus requiring it to have high densities and the necessary heat treatment process.

Transfer-resistant copper foil

• It is mainly used for printed circuit boards with high insulation requirements. If copper ion transfer occurs after the copper foil is made into a circuit board, it will have a considerable impact on the insulation reliability of the substrate. Therefore, special treatment (such as nickel plating, etc.) must be applied to the surface of the copper foil to inhibit further ionization and further transfer of copper.

Low-profile copper foil (LP copper foil), very low-profile copper foil (VLP copper foil)

• Mainly used on multilayer circuit boards, it requires a copper foil with a smaller surface roughness than ordinary copper foil. In addition, some high-frequency lines use copper foil, its surface is nearly smooth, that is, ultra-low profile copper foil (VLP copper foil), its surface roughness than ordinary copper foil is smaller. IPC-4562 in the provisions of the LP copper foil on both sides of the profile is not more than 10. 2 microns, and VLP copper foil on both sides of the profile is not more than 5.1 microns.

Glued copper foil

• Glued copper foil mainly includes adhesive-coated copper foil (ACC) and adhesive-backed copper foil (RCC), which is mainly used in the manufacture of paper-based copper-clad panels, with a resin layer applied to the roughing surface of the electrolytic copper foil after the roughing process. Back-glued copper foil is composed of copper foil with roughing, heat-resistant and anti-oxidation treatment on the surface and resin in stage B. The resin layer of backing copper foil has the same processability as the FR-4 bonding sheet, therefore, it is also considered that RCC is an emerging CCL product without glass fiber that is easy to be processed by laser, plasma, and other etching holes.

Carrier copper foil

• Most of the production of ultra-thin copper foil uses a certain thickness of metal support foil as the cathode, on which copper is electrodeposited, and then the plated ultra-thin copper foil together with the cathode support metal foil is hot pressed and cured and pressed on the insulating material board, and then the metal support foil used as the cathode is removed by chemical or mechanical methods. This kind of ultra-thin copper foil electrodeposited on the carrier is called carrier copper foil, as electrodeposited carrier metal can include: stainless steel, nickel, lead, zinc, chromium, copper, aluminum, etc., but some of the above metals are not easy to process into foil; some are too expensive to process into foil; some are processed into foil with too many sand holes; some surface is not easy to handle, and there is pollution to the copper foil. Therefore, the most practical and economical support body is aluminum foil.

Untreated copper foil

• There are two types of untreated copper foil: one is copper foil without enhanced bonding treatment on the surface and without rust prevention treatment (code N); the other is copper foil without enhanced bonding treatment on the surface but with rust prevention treatment (code P). Usually, the latter type of copper foil is more widely used, such as some copper foils for lithium-ion batteries, shielding copper foils, etc.

There are many types of electrolytic copper foil according to different divisions. With the development of electronic and electronic information technology, many newer and higher requirements are put forward for electrolytic copper foil in terms of variety and quality, prompting faster development of copper foil technology, and more and more varieties and specifications of electrolytic copper foil are available.