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This paper summarizes the supply chain pattern of special electrolytic copper foil, special resin and special glass fiber cloth used in new and high-end substrate materials in recent years, as well as the new performance requirements of these three materials.
Since 2020, the spread of the global new crown epidemic has led to serious changes in the supply and demand chain of copper cladding materials in China, and since the development of 5G, there have been huge changes in technology, performance and variety. Substrate materials for high-frequency and high-speed circuits, high HDI and IC packaging boards. In the face of these two major changes, we will explore the supply chain pattern of copper foil for new high-end substrate materials.
Performance Differentiation of Low-Cross Section Electrolytic Copper Foil in Different Applications
The types and varieties of thin electrolytic copper foils used in high-frequency and high-speed circuits are divided into five categories according to their application areas: thin electrolytic copper foils for rigid RF/microwave circuits; thin electrolytic copper foils for high-speed digital circuits; thin electrolytic copper foils for flexible PCBs; thin electrolytic copper foils for hermetically sealed loading boards; and thin electrolytic copper foils for thick copper PCBs. These five application areas are characterized by different performance requirements for thin electrolytic copper foils used in high-frequency and high-speed circuits, i.e., there is a certain emphasis on performance items and differences in performance indicators.
The performance requirements and differences of thin electrolytic copper foils used in the five main application areas are summarized in the following aspects:
(1) Thin electrolytic copper foil for rigid RF/microwave circuits
Thin electrolytic copper foils for RF/microwave circuits show more pronounced relative differences at different application frequencies. The requirements are more stringent due to factors such as passive intermodulation.
For this reason, copper cladding for high-end RF-microwave electronic substrates (e.g., substrates for millimeter-wave automotive radar) generally requires a pure copper treatment to support the reduction of passive intermodulation (PIM) and to achieve the low PIM characteristics of the laminates. The reference index is below -158DBC to -160DBC. The copper cladding is arsenic-free.
At the same time, the selection of RZ copper cladding varies greatly depending on the resin substrate of the cladding.
Rigid RF/microwave circuits with low-profile electrolytic copper foil in the copper foil specification grid thickness, general purpose: 18μm, 35μm, 70μm, as well as high-end very low or ultra-low-profile copper foil, thickness specifications for multi-purpose: 9μm, 12μm, 18μm varieties.
(2) Thin electrolytic copper foil for high-speed digital circuits
Thin electrolytic copper foils for high-speed digital circuits are mostly used in the centimeter-wave frequency range (3-30 GHz). The main application endpoints are high and mid-range servers. The performance of this type of copper foil has a more important effect on the insertion loss of the substrate and on the processability of the substrate, and therefore it is subject to stringent requirements. At the same time, thinness and low cost are also important requirements. Thin electrolytic copper foils for high-speed digital circuits are generally available in thicknesses of 18 μm, 35 μm, and 70 μm, as well as high-end very-low or ultra-thin copper foils in thicknesses of 9 μm, 12 μm, and 18 μm.
The author of various copper foil low Rz (HVLP, VLP, RTF and other varieties) of pressed profiles carried out a variety of investigations, comparisons, guidance, and came to the conclusion that: in similar varieties of brands, regardless of the SI relationship between the better varieties of non-pressure surface profile (Rz or Ra) is generally lower. For example, RTF copper foils from foreign companies with RZ = 3.0 μm (typical) generally have lower unpressed surface profiles (Rz or Ra). Surface RZ = 3.5 μm. Therefore, both RF/microwave circuit boards and high-speed digital circuit boards, in order to pursue better Si performance, it is also necessary to use contour shaped Cu foils with non-pressed surface RZ (or Ra, RQ), which also have a very low contour.
One of the most important types of low-profile Cu foils used in high-speed digital circuits is the reverse copper foil (RTF). In recent years, copper foil companies in Japan and Taiwan have made progress in RTF copper foil technology, with several varieties with RZs less than 2.5 μm already available, and even varieties with RZs less than 2.0 μm. As a result, the application market and the global market size of low-profile copper foils used in high-speed digital circuits have expanded rapidly.
Currently, the global copper thin electrolytic copper cladding manufacturing industry tends to use the same types of copper cladding for rigid RF/microwave circuits as for high-speed digital circuits. For example, CircuitFoil's 2019 BF-NN/BF-NN-HT ultra-low-profile copper foils from Luxembourg, which are in mass production, have achieved “dual compatibility”: first, they have evolved from BF-ANP copper foils, which are only used in PTFE resin-based substrates, to “BF-ANP” copper foils, which include polyphenylene ether (PPE) and polyphenylene ether (PPE) substrates. Including polyphenylene ether (PPE/PPO) resin system. Also suitable for pure or modified fluoropolymer (PTFE) resin systems.” Secondly, it can be applied to RF and microwave high-frequency boards and is also suitable for high-speed boards for high-speed digital circuits.
circuit board
(3) Thin Electrolytic Copper Foil Flexible PCBs
Thin electrolytic copper foils are used for flexible PCBs. Due to the need to manufacture fine wires, most of them are made of extremely thin copper foils (without carriers). Currently, the minimum thickness of this type has reached 6μm, such as Fidelity Metal Foils Powder Co., CF-T4X-SV6, CF-T49A-DS-HD2; and Mitsui Metal's 3EC-MLS-VLP (minimum thickness 7μm).
Low-sectional electrolytic copper-clad flexible PCBs also require copper cladding with high tensile strength and high elongation. The excellent transparency of the etched base film is also an important demand item in the copper foil market.
In recent years, the thin electrolytic copper foil used in high-frequency flexible PCBs has begun to develop towards thinness, and now there are many varieties in the industry with RZ less than 1.0um. For example, Mitsui Metal TQ-M4-VSP RZ≤ 0.6 (Typical); Foton Metal CF-T4X-SV Rz=1.0 (Typical, 9/12/18); Foton Metal CF-T49A-DS-HD2,Rz= 1.0μm (Typical) (6/9/12/18); Progressive ISP, RZ≤ 0.55 (Typical). 0.55 (typical).
(4) Low Cross Section Electrolytic Copper Clad IC Sealed Loading Boards
The low profile electrolytic copper foils required for sealing and loading boards (including module substrates) should have high tensile strength, high thermal stability, high modulus of elasticity, and high temperature (210°C/1h after treatment) peel strength. The thickness specification is 5.0μm to 12μm,and in recent years,the thickness specification of copper foils for high-end IC packaging boards is developing in the direction of even thinner thickness, i.e., the thickness reaches 1.5μm to 3μm.
In recent years, the high frequency and high speed requirements for packaging boards (including module substrates) have also emerged.As a result,more types of low-sectional electrolytic copper foils for packaging boards have appeared in recent years. For example, Mitsui Metal's 3EC-M2S-VLP (without carrier), Rz ≤ 1.8μm (typical);tensile strength 51kgf/mm 2 at 210°C/1h; elongation 4.6%;copper foil up to 9μm;Mitsui Metal's MT18FL (with carrier), RZ ≤ 1.3μm, copper foil for molded circuits specifications of 1.5, 2, 3μm.LPF (without carrier) RZ ≤ 1.72μm. LPF (without carrier),RZ≤1.72 (typical),210℃/1h tensile strength 52.3 KGF /mm 2;elongation 3.7%;copper foil thinnest size of 9μm.
(5) Thin electrolytic copper foil for high current thick copper PCBs
Low profile electrolytic copper foils are used for high current thick copper PCBs with a thickness of ≥105um (3oz). Commonly used specifications are 105, 140, 175, 210 μm. ultra-thick electrolytic copper foil has special thickness requirements, thickness specifications up to 350 μm (10oz), 400 μm (11.5oz).
High current thick copper PCBs with low profile electrolytic copper foils are mainly used for high current, power supply substrates, and high heat dissipation circuit boards. The thick copper PCBs are mainly used in automotive electronics, power supply, high power industrial control equipment, solar energy equipment, etc. In recent years, the conductivity of PCBs has been increasing. In recent years, the thermal conductivity of PCBs has become one of the most popular and important features. The market for ultra-thick copper foil is expanding. At the same time, the development of thick copper PCB thin-wire technology and applications in the manufacturing industry requires the use of ultra-thick copper foils with thin features. Mitsui Metals RTF type thin, e.g. thick copper foil: MLS-G (Type II), Rz = 2.5 micron (typical) product. Luxembourg TW-B, Rz ≤ 4. 2 µm (product specification)
Market Expansion and Performance Requirements for Ultra-Thin Electrolytic Copper Cladding for IC Cover Carriers
In a recent paper written by an overseas PCB expert, the application market and performance requirements for ultra-thin, low-profile copper foils are described. The paper suggests, “Since 2017, HDI boards have begun to adopt a large number of IC board products are widely used in the line plating process. The process is called semi-additive process (SAP), is the use of line plating technology to meet the IC board less than 15μm line structure requirements, this process has become the mainstream of HDI after the manufacturing process does not use the general HDI board PCB production process, but the use of ultra-thin copper plate semi-additive technology (MSAP) adjustments.”
“The difference between Semi-Additive Processing (SAP) for ICs and MSAP with copper foil for SLPs is whether or not the processed boards are pre-pressurized ultra-thin copper foil. The current proven SAP process is usually an ABF thin film material with a full-plate precipitated copper process, which is not suitable for most of the existing production equipment. This has led to an improved solution, the semi-additive process for ultra-thin copper foils.”
This article gives a comparison of the semi-additive process (MSAP) with ultra-thin copper foils (see Figure 2). The location of “pre-pressurized ultra-thin copper foil” is labeled here to give the reader a clear picture.
The key to the copper-clad semi-additive process is the use of carrier copper, which helps to stabilize the peel strength of the copper foil and enhance the support of the fibers,” the paper suggests. Thin copper foils, which are coated on the substrate by pressing, are characterized by high and stable peel strength, thickness uniformity of the ultra-thin foils, low surface roughness, suitable resistance to oxidative coating of the smooth surfaces of the foils, etching of fine circuits, etc. The main features of the thin copper foils are the high peel strength, the uniform thickness of the foils, the low surface roughness, the suitable resistance to oxidative coating of the smooth surfaces of the foils, and the high resistance to etching of the finer circuits. Among them, copper foil peel strength is the most important performance item.