Introduction: This paper describes the supply chain structure of new and high-end substrate materials, such as special electrolytic copper foil, special resin and special fiberglass cloth, and their new performance requirements.

Since the beginning of 2020, the global new crown epidemic spread, resulting in China's copper clad laminate raw material supply chain pattern, has undergone serious changes. Since the development of 5G, the substrate materials of CCL, HDI and IC packaging board for high-frequency and high-speed circuits have evolved greatly in technology, performance and variety. In the face of these two important changes, in-depth study of new, high-end substrate materials used in electronic copper foil supply chain structure for some discussion.

1. Supply status of various low profile electrolytic copper foil and new characteristics of its market pattern

Global high-frequency high-speed electrolytic copper foil market size in 2019, as well as the pattern (each country/region, each major manufacturers market share) , see figure 1, Table 1.

Figure 12019 global low profile copper foil market size and pattern table 12018,2019 high-frequency high-speed circuit for low profile copper foil market pattern of statistical forecasts

Global Production and sales of low profile copper foil (the size of the market) are estimated to have increased by 49.8 per cent to 53,000 tonnes in 2019, as shown in figure 1, Table 1. It is estimated to account for 7.6% of the world's electrolytic copper foil. In 2019, the ratio of RTF to VLP + HVLP was about 77:23. However, the proportion of VLP + HVLP will increase in the next few years. In 2019, domestic and foreign invested copper foil enterprises produced a total of 7,580 tons of low profile copper foil, of which domestic invested enterprises accounted for 51.2% (3,880 tons) . Domestic enterprises low profile electrolytic copper foil production and sales, accounting for the entire domestic enterprise electronic circuit copper foil production (144,000 tons) of 2.7% . In 2019, domestic enterprises achieved a new breakthrough in VLP + HVLP varieties can be mass produced, but the production and sales of such low profile copper foil is very small, only 2.3% of the global total production and sales of such electrolytic copper foil.

2.New Characteristics of the variety and performance requirements of low profile electrolytic copper foils for high frequency and high speed circuits

2.1 electrolytic copper foil varieties and low profile properties corresponding to different transmission loss grades for high frequency and high speed CCL

In order to achieve better Signal Integrity in high-frequency and high-speed circuits, Signal Integrity need to achieve (especially in high-frequency) lower Signal transmission loss performance. This requires the conducting material used in the manufacture —— Copper foil with low profile. That is, copper clad laminate manufacturing using copper foil is low Rz, low Rq varieties. Four levels of signal transmission loss can be used in accordance with the various low profile copper foil varieties, Rz requirements and their main manufacturers, as shown in Table 2. Table 2 also shows the ranking of low profile copper foil requirements in the substrate transport loss class of CCL. Table 2. RZ index ranges of electrolytic copper foil for high frequency and high speed CCL with different transmission loss grades

2.2 different kinds of low profile electrolytic copper foils for high frequency high speed circuits with different properties of low profile electrolytic copper foils for different application fields are classified into five categories according to their application fields. Low profile electrolytic copper foil for rigid rf/microwave circuit; low profile electrolytic copper foil for High Speed Digital Circuit; low profile Electrolytic Copper Foil for flexible PCB; low profile electrolytic copper foil for packaging board; low profile electrolytic copper foil for thick copper PCB. These five application areas, the high-frequency high-speed circuit for low profile electrolytic copper foil, in the performance requirements have different characteristics, that is, there are some emphasis on performance items, performance indicators are different. The performance requirements and differences of low profile electrolytic copper foils for five application areas are as follows:

(1) low profile electrolytic copper foil for rigid rf/microwave circuits, the relative differences are more obvious under different application frequencies. The requirements are more strict for the influence factors of copper foil performance on DK uniformity, signal transmission loss, processing layer free of ferromagnetic elements, Passive modulation, etc. . For this reason, the copper foil used in high-grade rf/microwave circuit substrates (such as millimeter-wave vehicle radar substrates) generally requires pure copper surface treatment process to reduce the PIM and realize the low PIM of the CCL, target: ACHIEVE-158 DBC ~-160 DBC. The treatment layer of copper foil realizes non-arsenization. At the same time, this kind of copper foil is very different in the choice of different Rz copper foil due to the different resin base materials. Low profile electrolytic copper foils for rigid rf/microwave circuits are generally used in the thickness specifications of copper foil: 18 M, 35 m, 70 m, while the high-end extremely low or ultra-low profile copper foils are commonly used in the thickness specifications: 9 M, 12 M, 18 M.

(2) the application market of low profile copper foil for high-speed digital circuits is mostly located in the frequency range of CM wave (3 ~ 30GHZ) . Its main application terminal is high-end server and so on. The performance of this kind of copper foil has more important influence on the insert loss of substrate and the processability of substrate. At the same time, thin copper foil specifications, low-cost is also an important requirement. Low profile electrolytic copper foils for high-speed digital circuits are commonly used in the thickness specifications of copper foils: 18 M, 35 m, 70 m, while the high-end extremely low or ultra-low profile copper foils are commonly used in the thickness specifications: 9 M, 12 M, 18 M. This paper investigates and compares the profile of non-press-fit surfaces of many kinds of copper foil with low Rz, including HVLP, VLP, RTF , etc. , where the performance in the SI is better varieties, its non-compacting surface profile (in Rz or Ra) is generally lower. For example, an RTF copper foil product of a foreign-funded enterprise, it has a Rz = 3.0 m (typical) , rather than a Rz = 3.5 m. Therefore, both Rf/microwave Circuit Boards and high-speed Digital Circuit Boards require the non-pressed Rz (or Ra, Rq) of the copper foil with the first profile for better SI performance and also have very low profile. Currently, high-speed digital circuits using low profile copper foil is an important class of inverting copper foil (RTF) . In recent years, Resin Japan, Taiwan and other copper foil enterprises in RTF copper foil technology, its Rz less than 2.5 m many varieties have been published, even Rz less than 2.0 m varieties have also appeared. This also makes its application market, as well as the global high-speed digital circuit with low profile copper foil market size proportion of the variety, has also been rapidly expanded. At present, the global copper foil low profile electrolytic copper foil manufacturing industry, rigid rf/microwave circuit and high-speed digital circuit copper foil varieties, more tend to the same performance. For example, Luxembourg Circuit Copper Foil Co. , Ltd. (CircuitFoil) in 2019 to achieve large-scale production of ultra-low profile copper foil bnn/bnf-NN-HT. This variety has achieved "two compatibility" : first, the original BF-ANP copper foil only used for PTFE resin type substrate, developed to "including PPE/PPO resin system. It can also be used in pure or modified fluoropolymer (PTFE) resin system."Second, it can be used in RF Microwave Circuit Board and high-speed Digital Circuit Board.

(3) low profile electrolytic copper foil for flexible PCB. Because of the need of manufacturing micro circuit, the thin copper foil (without carrier) is usually used. The current minimum thickness specifications of these varieties have reached 6M, such as Fukuda Metal Foil Powder Joint-stock Company CF-T4X-SV6, CF-T49A-DS-HD2; and Mitsui Metal Co. , Ltd.'s 3EC-MLS-VLP (minimum thickness 7M) . Low Profile Electrolytic Copper Foil for flexible PCB also requires high tensile strength and high elongation of copper foil. The excellent transparency of the etched substrate is also an important demand item in the copper foil market. Low profile electrolytic copper foils for high frequency flexible PCB are becoming low profile in recent years. There are a number of Rz less than 1.0 um varieties in the industry. For example, Mitsui Metal TQ-M4-VSP RZ ≤0.6(typical value) ; Fukuda Metal CF-T4X-SV Rz = 1.0(typical value, specification 9/12/18) ; Fukuda Metal CF-T49A-DS-HD2, Rz = 1.0 m (typical value)(specification 6/9/12/18) ; progressive ISP, Rz ≤0.55(typical value) .

(4) low profile electrolytic copper foil for IC packaging board (including module substrate) should have high tensile strength, high thermal stability, high elastic modulus and high peel strength at high temperature (210 °c/1h) . Its thickness specification is 5.0 m ~ 12 M. And in recent years, the thickness specification of copper foil for high-end IC packaging board is developing to be thinner, I. E. 1.5 m ~ 3 M. High-frequency and high-speed packaging boards (including module substrates) have also been in demand in recent years. Therefore, more and more low profile electrolytic copper foils for package boards have appeared in recent years. For example, Mitsui Metal 3EC-M2S-VLP (without carrier) , R Z ≤1.8 m (typical value) , tensile strength 51kgf/mm 2 at 210 °c/1h, elongation 4.6% , and the thinnest specification of Copper Foil 9 M. MT18FL (carrier) of Mitsui Metal, R Z ≤1.3 m, forms the specification of circuit copper foil 1.5,2,3 M. Rz ≤1.72(typical value) , tensile strength 52.3 KGF/MM 2 at 210 °c/1 H, elongation 3.7% , and the thinnest specification of copper foil 9 M. (5) high current thick copper PCB with low profile electrolytic copper foil thickness specification ≥105um (3oz) , high current thick copper PCB with low profile electrolytic copper foil, commonly used specifications: 105,140,175,210 M. There are special thickness requirements of super-thick electrolytic copper foil, thickness specifications up to 350 m (10oz) , 400 m (11.5 Oz) . High current thick copper PCB with low profile electrolytic copper foil, mainly used for high current, power substrate, high heat dissipation circuit board manufacturing. The produced thick copper PCB is mainly used in automotive electronics, power supply unit, high power industrial control equipment, solar energy equipment and so on. In recent years, the thermal conductivity of PCB has become one of the most important functions. The market demand for ultra-thick copper foil is expanding. At the same time, because of the development of thin circuit manufacturing technology and application of thick copper PCB, the ultra-thick copper foil is required to have the characteristics of low profile. For example, Mitsui RTF type low profile thick copper foil: MLS-G (type II) , rZ = 2.5 M. Luxembourg TW-b, R Z ≤4.2 m (product index). Application market expansion and performance demand of ultra-thin electrolytic copper foil for 3ic packaging board a recent paper written by overseas PCB experts gives a penetrating exposition of the application market and performance requirements of ultra-thin and low profile copper foil. "since 2017, HDI board has been widely used in IC board products, which has been widely used in line plating process. This process, known as semi-additive process (SAP) , uses line plating technology to meet the structural needs of lines with IC boards less than 15 meters. This process has not been adopted in HDI boards, but it has become the mainstream process of HDI manufacturing by using ultra-thin copper sheet as semi-additive technology (MSAP) . At present, the mature SAP processes are all ABF thin films, which is not suitable for most of the existing production equipment. Therefore, an improved scheme, that is, semi-addition process with ultra-thin copper foil (MSAP) , has come into being. The paper gives the comparison chart of the process route of semi-addition process with ultra-thin copper foil (see Fig. 2) , on which the author marks the position of "pre-pressed ultra-thin copper foil" , so that readers can have a clear understanding.

Fig. 2sap and MSAP process flow comparison it is proposed that "the key to the semi-addition process with copper foil is the use of copper carrier, which helps to stabilize the peel strength of copper foil and strengthen the fiber support. " However, at the same time, some important properties of ultra-thin copper foil, which is pressed on the substrate, should be achieved in micro-circuit and micro-hole laser processing, are also mentioned. It mainly includes: High and stable copper foil peel strength, ultra-thin copper foil thickness uniformity, low Surface roughness, copper foil on the surface of suitable anti-oxidation coating, micro-circuit etching. Among them, the peel strength of copper foil is the most important performance item. 

Source: PCBWORLD