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- December 16, 2022
- PCB news
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- 05 mins
An overview of PCB copper foil
Copper foil is a negative electrolytic material, a thin, continuous metal foil deposited on the base layer of the circuit board, which acts as a conductor of the PCB. It easily adheres to the insulating layer, accepts the printed protective layer, and forms a circuit pattern after etching. The copper mirror test is a flux corrosion test using a vacuum deposited film on a glass plate.
Copper foil is made of copper plus a certain proportion of other metals. Copper foil generally has two types of 90 foil and 88 foil, that is, the copper content is 90% and 88%, and the size is 16*16cm. Copper foil is the most widely used decorative material. Let’s see some facts about PCB copper foil!
PCB copper thickness
International PCB copper thickness commonly used are: 35um, 50um, 70um.
Generally, the thickness of single and double layer PCB copper foil (copper clad) is about 35um (1.4mil), and the other specifications are 50um and 70um. The thickness of the surface layer of the multilayer board is generally 35um=1oz (1.4mil), and the inner layer is 17.5um (0.7mil). 70% of the circuit boards use a copper foil thickness of 35um, which mainly depends on the use of the PCB and the voltage and current of the signal; in addition, for PCBs that require excessive current, some will use 70um copper thickness, 105um copper thickness , there will rarely be 140um and so on.
The thickness of copper skin is usually expressed in oz (ounces). 1 oz refers to the thickness of copper evenly covered by 1 oz of copper on an area of 1 square foot, which is about 1.4 mil. It expresses the average thickness of copper foil by the weight per unit area. Expressed by formula, that is, 1oz=28.35g/ FT2 (FT2 is square feet, 1 square feet=0.09290304 square meters).
The thickness of the copper skin is different for different purposes. The common ones are 0.5oz, 1oz, and 2oz, which are mostly used in consumer and communication products. More than 3oz are thick copper products, mostly used for high current, such as high voltage products, power boards.
The thickness of the copper skin (trace width) will affect the magnitude of the current. Although there is already a formula that can directly calculate the maximum current carrying capacity of copper foil, it is not only so simple in the actual design of the circuit, so the safety factor should be fully considered in the design.
Characteristics of copper foil
Copper foil has a characteristics of low surface oxygen, so it can be attached to various substrates, such as metals, insulating materials, etc., and has a wide temperature range. Mainly used in electromagnetic shielding and antistatic. The conductive copper foil placed on the substrate surface and combined with the metal substrate, has excellent conductivity and provides the effect of electromagnetic shielding. It can be divided into: self-adhesive copper foil, double-lead copper foil, single-lead copper foil, etc.
Electronic grade copper foil (purity above 99.7%, thickness 5um-105um) is one of the basic materials of the electronics industry. With the rapid development of the electronic information industry, the use of electronic grade copper foil is increasing. The products are widely used in industrial calculators, communication equipment, QA equipment, lithium-ion batteries, civilian TV sets, video recorders, CD players, copiers, telephones, heating and cooling air conditioners, automotive electronic components, game consoles, etc.
There is an increasing demand for electronic-grade copper foil, especially high-performance electronic-grade copper foil in global markets. Relevant professional organizations predict that by 2025, China’s demand for electronic-grade copper foil will reach 300,000 tons, and China will become the world’s largest production base for printed circuit boards and copper foil. The market for electronic-grade copper foil, especially high-performance foil, is promising.
Global supply status of copper foil
Copper foil for industrial use can be commonly divided into two categories: rolled copper foil (RA copper foil) and electrodeposited copper foil(ED copper foil). Among them, rolled copper foil has good ductility and other characteristics, and is used in the early FPC process. While electrolytic copper foil has the advantage of lower cost than rolled copper foil.
Since rolled copper foil is an important raw material for FPC PCB, the improvement of the characteristics and price changes of rolled copper foil will have a certain impact on the FPC industry.
Since there are fewer manufacturers of rolled copper foil, and the technology is in the hands of some manufacturers, customers have a low degree of control over the price and supply. Therefore, on the premise of not affecting product performance, electrodeposited copper foil is used instead of rolled copper foil.
However, if the physical characteristics of the copper foil structure will affect the etching factors in the next few years, the importance of rolled copper foil will increase again in thinner or thinner products, and in high-frequency products due to telecommunications considerations.
There are two major obstacles in the production of rolled copper foil, resource barriers and technical barriers. The resource barrier refers to the fact that the production of rolled copper foil needs to be supported by copper raw materials, and it is very important to occupy resources. On the other hand, technical barriers deter more new entrants, in addition to rolling technology, surface treatment or oxidation treatment technology is also included.
Most of the global manufacturers have many technical patents and key technology Know How, increasing the barriers to entry. It is difficult for new entrants to successfully enter the market if they process production after harvesting and are subject to cost constraints from large manufacturers. Therefore, the global rolled copper foil market is still a strong monopoly.
The development of copper foil
Copper foil is an important material for copper clad laminate (CCL) and PCB. In the rapid development of today’s electronic information industry, electrolytic copper foil is called: the “neural network” of electronic product signal and power transmission and communication.
Since 2002, the production value of China’s printed circuit boards has entered the third place in the world, and as the substrate material of PCBs, copper clad laminates have also become the third largest producer in the world. As a result, China’s electrolytic copper foil industry has developed by leaps and bounds in recent years.
In order to understand and understand the past, present, and future of the development of the world and China’s electrolytic copper foil industry, experts from the China Epoxy Resin Industry Association will review its development.
From the perspective of the production department and market development of the electrolytic copper foil industry, its development process can be divided into three major development periods: the period when the United States created the first world copper foil enterprise and the electrolytic copper foil industry started; the period when Japanese copper foil enterprises fully monopolized the world market; the period when the world’s multi-polar competition for the market.
