Design of lead-free compatible copper-clad laminates

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Shi Jianying (Factory 704, Xi’an City, Shaanxi Province, 710029) Abstract: This paper introduces the basic concepts, design methods, interface control techniques, manufacturing technologies, production process techniques for lead-free compatible copper-clad laminates, as well as the issues that need attention. Keywords: lead-free compatible copper-clad plate ； Matrix resin ； Manufacturing Process Technology 0 Introduction The official implementation of the two EU directives marked the beginning of an era of lead-free soldering in the global electronics industry. As the soldering temperatures increased, higher requirements were placed on the heat resistance and thermal reliability of copper-clad laminates ； With the advancement of multi-layer printed circuits and IC packaging technologies, in order to enhance the reliability and stability of interconnections and packaging, copper-clad laminates are required not only to have high heat resistance but also a low coefficient of thermal expansion (CTE). To this end, the industry both domestically and internationally is actively developing copper-clad laminates that are lead-free, compatible, and feature high heat resistance as well as a low coefficient of thermal expansion. This article discusses with peers the basic concepts, design process, manufacturing technologies, production techniques, as well as the issues that need attention in the design of lead-free compatible copper-clad laminates. In addition to meeting the performance requirements of ordinary FR-4 copper-clad laminates, lead-free compatible copper-clad laminates must also possess the following properties: (1) A high glass transition temperature Tg. The glass transition temperature Tg is the temperature at which a polymer transitions from a glassy state to a highly elastic state. Both the glassy state and the elastomeric state are solid states; the temperature at which these two states transform into each other is called the glass transition temperature. The glass transition temperature is an important parameter for the physical changes that occur in polymers. It is mainly related to the structure of the polymer, its aggregation state, cross-linking density, etc. The glass transition temperature is not a fixed value; it varies depending on the measurement methods and conditions, but it is an important process parameter for polymers. Above this temperature, the polymer exhibits \"elasticity\", while below it it exhibits \"brittleness\". ⑵ It has a high thermal decomposition temperature, Td – that is, the temperature at which the polymer begins to decompose. Thermal decomposition is a chemical reaction and an important parameter for the chemical transformation of polymers. For copper-clad laminates, it refers to the temperature at which the material decomposes when heated, when the thermal weight loss reaches 5%. The thermal decomposition temperature is mainly related to the structure of the polymer, the decomposition activation energy, its aggregation state, and the cross-linking density. ⑶ The thermal delamination times T288 and T300 refer to the time it takes for a copper-clad laminate, at a constant temperature (not exceeding 35°C), to be heated at a steady rate of 10°C/min to the set temperature of 288°C or 300°C. It remains at this temperature until irreversible changes in thickness occur in the sample, that is, delamination takes place. The layering time is mainly related to the structure and properties of the matrix resin, the interfacial structure between the matrix resin and the reinforcing material, the interfacial adhesion condition, as well as the Tg and Td of the substrate material. T288 and T300 are the most direct and straightforward methods for evaluating the thermal properties of copper-clad laminate materials; they represent a comprehensive indication of parameters such as the Tg, Td, Z-CTE of these materials, as well as their interfacial structure and adhesion quality. 4) Low coefficient of thermal expansion (CTE): The CTE refers to the dimensional changes in the x, y, and z directions that occur in a copper-clad plate when it expands due to heat. During the welding process, whether it is lead-free welding or lead-based welding, the welding temperature is much higher than the Tg of the matrix resin; in other words, during welding the matrix resin in the substrate is in a rubbery state. For copper-clad laminates, since plain glass fiber cloth with a two-dimensional woven structure is used as the reinforcing material, the CTE variations in the x and y directions are very small; therefore, thermal expansion is mainly reflected in changes in the Z-CTE, especially the change in Z-CTE (α2) above the glass transition temperature, which is significant. After curing, the volume of a copper-clad plate consists of two parts: the occupied volume (matrix resin, reinforcing glass fibers, filler materials, etc.) and the free volume (voids or air gaps). The occupied volume is an inherent property; when the substrate material is heated, molecular motion intensifies, and the increase in the amplitude of molecular vibrations along with changes in bond lengths lead to volume expansion. Once the material has been selected, its occupied volume remains an inherent characteristic that cannot be changed. Therefore, to reduce the CTE of a substrate material, it is necessary to reduce its free volume. The free volume is primarily reduced by increasing the cross-linking density, adding filler materials (especially a small amount of whisker materials), improving the interface structure and interfacial adhesion strength, and selecting appropriate lamination processes and cooling methods, in order to lower the CTE, particularly the Z-CTE. In addition to considering the above-mentioned properties, lead-free compatible copper-clad laminates also require attention to their processability and workability, particularly the control techniques for the interfaces between the constituent materials. 1 Design of lead-free compatible copper-clad laminates. Copper-clad laminates are a type of thermosetting resin-based functional composite material – they are composed of reinforced glass fiber cloth, filler materials, matrix resin, various additives, and copper foil. Therefore, the design of lead-free compatible copper-clad laminates should conform to the basic concepts and design principles of composite material design. Copper-clad plate design should take into account the properties of the constituent materials, as well as the macroscopic, mesoscopic, and microscopic structures and properties of the composite material, in order to achieve the desired performance and structural characteristics. For decades, the vast majority of copper-clad plate designers have focused solely on the constituent materials and the macroscopic properties of the copper-clad plates, paying little attention to their micro- and nano-structures, especially the influence of interfacial effects on the macroscopic properties of these plates. This is very important and should draw the attention of peers in the industry. 1.1 Design Process Unlike traditional material design, the design of composite materials is more complex, involving the optimization of multiple design variables and multi-level design choices. The design of composite materials requires determining the geometric characteristics of the reinforcement agents (reinforcing materials, filler materials) such as continuous fibers, chopped fibers, whiskers, and particles, as well as the matrix material, the microstructure of both the reinforcing materials and the reinforcement agents, and their volume fractions. For given characteristics and performance specifications, conducting a systematic optimization design of the above variables is a rather complex task. Sometimes, the design of composite materials relies entirely on experienced designers making judgments using existing theoretical models. Generally speaking, the design process can be roughly divided into the following steps: design requirements (performance requirements) → material selection → optimization design → evaluation of the performance of representative units → completion of the final (product) design. ⑴ Design requirements: The design parameters are determined by understanding the product’s requirements regarding performance in terms of the environment and applied loads, such as mechanical loads, thermal loads, exposure to humid conditions, as well as electrical, insulation, and dielectric properties. ⑵ Material selection: Based on the requirements of the design parameters, the matrix resin, reinforcing materials, filler materials, geometric shape, and various additives are selected. ⑶ Optimized design: Optimize the design formula, manufacturing method, process conditions, and production process of the matrix resin. ⑷ Performance evaluation: Perform performance tests on representative units to determine the quantitative relationship between performance and the constituent materials as well as the microstructure. ⑸ Complete the final product design: Based on the performance evaluations, improve and refine the design to produce a final product that meets the requirements of the design specifications. 1.2 Material Design The design of composite materials generally refers to the process of creating the desired material by combining several raw materials. The raw materials referred to here mainly include matrix resin, reinforcing materials, filler materials, and conductive materials. Composites made from different raw materials will have different properties. Moreover, different weaving patterns of the fibers (three-dimensional woven fabrics, plain weaves, twill weaves, satin weaves, checkweave non-woven fabrics, etc.) result in different properties for the composites formed with the matrix material. For laminated composites, which are composites composed of fibers and a matrix, the basic unit is a single-layer material (i.e., prepreg or semi-cured sheet, which represents the primary structure of the composite). Laminated materials are structural composites formed by stacking single-layer materials (they belong to the secondary structure of composites). Therefore, composite material design includes raw material selection, determination of single-layer materials, and design of composite laminates. 1.2.1 Selection of raw materials The selection of raw materials has a significant impact on the properties of composite materials; by choosing the appropriate raw materials, composite materials with the desired properties can be obtained. Generally, the criteria for comparing and selecting materials vary depending on their intended use, and mainly include physical properties, manufacturing processes, workability, cost, and other factors. General principles for selecting raw materials: high specific strength and high specific stiffness ； Principles of environmental (including processing) adaptability of materials ； Principles for meeting special performance requirements ； Principles for meeting process requirements ； The principle of low cost and high efficiency 1.2.2 Selection of reinforcing fiber materials When selecting reinforcing fibers, it is first necessary to determine the category of the fibers, and then to identify the type, specifications, and weaving pattern of those fibers. The selection of fiber types is based on the function of the structure, with fibers chosen that meet certain mechanical, physical, and chemical properties. In addition to using single fibers, hybrid materials composed of a mixture of various fibers can also be chosen. 1.2.3 Selection of matrix resin The selection of the matrix resin should meet the following requirements: 1) It must be able to function properly within the operating temperature range. That is, to meet various thermal loads. 2) It possesses certain mechanical properties to meet mechanical loads. 3) The elongation at break of the matrix resin should be greater than or close to that of the fibers, to ensure the reinforcing effect of the fibers. 4) It possesses physical, chemical, electrical, and other properties that meet the requirements for use. It mainly refers to electrical properties, insulation properties, dielectric properties, moisture absorption, resistance to media, flame retardancy, low smoke production, and low toxicity. 5) It possesses certain processability. It mainly refers to the viscosity of the resin, gelation time, and volatile content, as well as factors such as the shelf life of the prepreg and the processing time, the temperature, pressure, and time required for curing, and the dimensional shrinkage after curing. 1.3 Interface control technology As we know, in any system where different phases coexist, there are interfaces between those phases. Composites are a combination of reinforcements (reinforcing materials, filler materials) and matrix resin. It endows composite materials with properties that the individual constituent materials do not possess. Due to the presence of interfaces in composite materials, the roles played by the reinforcement and the matrix resin are both independent and interdependent. The interface is an important component of composite materials; its structure, properties, and bonding strength are directly related to the performance of the composite materials. Therefore, research on interface control technology for composite materials is of great significance. Composites are multiphase materials formed by combining two or more substances with different physical and chemical properties at the micro, meso, or macro scale (for example, lead-free compatible copper-clad laminates contain 4 solid phases and 6 phase interfaces). The interface formed by the contact between various phases in composite materials is a layer with a certain thickness (on the nanometer or sub-micrometer scale). Its structure varies depending on the matrix resin and the reinforcing agents, and it represents a new phase – the interfacial phase (interface layer) – that differs significantly from the matrix resin. This interfacial phase serves as a link between the reinforcing phases and the matrix resin, as well as a bridge for the transmission of stress and other information. Whether the reinforcement in composite materials is microfibers, whiskers, particles, or fibers, it undergoes varying degrees of interaction and interfacial reactions with the matrix resin during the manufacturing process, resulting in interfaces of various structural types. Therefore, conducting in-depth research on the formation process of interfaces, the properties of the interface layer, interfacial adhesion, and the impact of stress transfer behavior on macroscopic properties, in order to effectively control the interfaces, is key to obtaining high-performance composite materials. Many composite materials have poor compatibility between their reinforcement agents and the matrix resin. To improve their compatibility, some modifiers such as coupling agents are added, thereby forming a new interface at the boundary between the two phases; the structure and properties of this new interface differ from those of the original phase boundary. Numerous facts demonstrate that the overall performance of a composite material composed of multiple components is not simply the sum of the individual component properties. Each component in such a composite plays its own role, but it is not isolated; rather, they influence and depend on one another. This interdependence is achieved through the interfaces between the component materials. The interfacial effects of composite materials mainly include: 1) Physical effects: those that cause changes in wetting, diffusion, compatibility, interfacial free energy, interfacial structure, and network interpenetration among the various components. 2) Chemical effects: The chemical bonds, which are formed by the interatomic forces within a molecule, determine the chemical properties of a substance. Similarly, the intermolecular forces at the interface determine the physical and chemical properties of the interface in the composite material. Chemical reactions on the interface will result in the formation of a new interface structure. According to the findings of modern interfacial science, the molecular forces present at an interface include: non-polar van der Waals forces (dispersion forces), polar van der Waals forces, hydrogen bond forces, acid-base interactions, as well as the combination and individual components of various forces between molecules. 3) Mechanical effects: Various stress distributions induced at the interface. The interface plays a decisive role in the fracture toughness of copper-clad laminate materials, interlayer shear, CTE, T288, T300, the dimensional stability and flatness of the sheets, delamination, as well as the materials’ response to humid and corrosive environments. The interfacial structure and interactions of composite materials are extremely complex. Scholars at home and abroad have explored the fine structure of interfaces, as well as the relationship between interface properties and the overall performance of composite materials, by studying the surface properties and morphology of reinforcements, surface modification and its characterization, the interaction between reinforcements and the matrix resin as well as interfacial reactions, and interface characterization. This research aims to optimize the design of composite material interfaces and to develop new types of composite materials. Interface control technology is widely used in the processes of resin production, impregnation, hot pressing, and material treatment for copper-clad laminates. For example: 1) In the resin production process: addition of filling materials, incorporation of coupling agents, thermoplastic elastomers, core-shell materials, as well as the sequence and method of adding these materials, high-speed shear, ultrasonic mixing, etc ； 2) During the impregnation process: single-coating pre-impregnation, increasing the siphon time, prolonging the impregnation time, vacuum impregnation, the method of injecting the resin paste, and the flow and circulation patterns of the paste, etc ； 3) Hot pressing process: bonding of copper foil to prepregs, bonding between prepregs, vacuum lamination technology, orientation and penetration of whiskers under pressure, determination of various process parameters in the molding die, etc. 4) Material processing: surface treatment of glass fiber cloth, fiber opening treatment, thinning, untwisting or low-twisting, surface treatment of copper foil, etc. The use of the above technologies and methods is aimed at improving the interface structure and the bonding condition of the interfaces, thereby enhancing the overall macroscopic properties of the copper-clad plate. 2 Manufacturing of lead-free compatible copper-clad laminates As mentioned earlier, copper-clad laminates are functional composite materials composed of E-glass fiber cloth, filler materials, matrix resin, additives, and copper foil. Through the analysis of the constituent materials, it was found that the main factors affecting the properties such as Tg, Td, T288, T300, and CTE of lead-free compatible copper-clad laminates are the matrix resin, reinforcing materials, filler materials, the structure of the phase interfaces, and the bonding condition at those interfaces. 2.1 Matrix Resin As illustrated by the above analysis, for lead-free compatible copper-clad laminates, a polymer synthetic resin with stable thermal properties and the ability to maintain good mechanical and physical properties under high-temperature conditions should be chosen as the matrix resin. These polymer-based synthetic resins must meet the following basic requirements: a. They must possess high thermophysical stability, namely a high softening point (Ts), a high melting point (Tm), and a high glass transition temperature (Tg). These properties are directly related to the aggregation state, crystallinity, heat enthalpy changes, and entropy changes of the polymer. b. It possesses high thermochemical stability, meaning that the polymer should have a high thermal decomposition temperature Td. Thermal decomposition is a chemical reaction, and the relationship between its thermal decomposition rate constant and the decomposition activation energy follows the Arrhenius equation K=Ae-△E/RT, where △E represents the decomposition activation energy, which corresponds to the bond energy between atoms. Therefore. △The larger E is, the smaller the thermal decomposition rate constant k becomes; thus, the polymer is less likely to decompose, and its thermal stability increases. c. Resistance to oxidation and ozonization, that is, resistance to aging. It must contain reaction groups capable of undergoing cross-linking chemical reactions. . . . . . . . In accordance with the above requirements, we can prepare the matrix resin using the following approach: Option 1: Improve the traditional FR-4 resin system. Traditional FR-4 copper-clad laminates find it difficult to meet the demands of lead-free soldering for high heat resistance and a low coefficient of thermal expansion. Based on the above analysis, by modifying the FR-4 resin system – that is, by removing all or part of the dicyandiamide (dicy) curing agent from the conventional FR-4 resin system and replacing dicy with thermoplastic phenolic resins or aromatic polyamine compounds such as diaminodiphenylmethane (DDM), diaminodiphenylsulfone (DDS), m-phenylenediamine (MPDA), and diamino-diphenyl ethers as curing agents for epoxy resins – it is possible to increase the presence of aromatic-heterocyclic structures in the epoxy cured products, thereby enhancing their heat resistance and reducing their CTE. Option 2: BMI/diamine-modified epoxy resin system. The diamine-modified bismaleimide system exhibits good heat resistance, mechanical properties and toughness, electrical properties, dimensional stability, and a low coefficient of thermal expansion. However, this resin system has poor processability. To improve its processability, epoxy resin can be introduced into the system; this not only enhances the processability of the resin system but also improves the adhesiveness of the BMI system. Meanwhile, the epoxy groups can react with secondary amine groups –NH– to form a cured cross-linked network. Option 3: Epoxy resin modified with cyanates. By using cyanate modification (curing) of the epoxy system, the molecular structure of the cured resin contains no polar groups such as hydroxyl or amine groups; as a result, its moisture absorption rate is low, and the resin matrix exhibits good resistance to humid heat. The cured resin contains pentagonal oxazole heterocyclic and hexagonal triazine ring structures, thus it possesses good heat resistance. At the same time, the molecular structure of the cured resin contains a large number of “—C—O—” ether bond structures, which gives it good toughness as well. Typically, the addition of about 30% cyanate ester is sufficient to cure bisphenol A epoxy resin at 180°C, yielding excellent process properties. Option 4: Cyanoate-modified bismaleimide resin system. The reaction between the cyanoate functional groups and the electron-deficient unsaturated double bonds in BMI is the basis for cyanoate-modified bismaleimides. The BT resin series of resins commercialized by the Japanese company Mitsubishi is a class of reaction products or mixtures of cyanate esters and BMI resins. The most basic components of BT resin are bisphenol A dicyanate and diphenylmethane bismaleimide. Based on cyanate ester-modified BMI, epoxy resins, acrylic resins, and thermosetting flame retardants can be added to obtain sheets that meet various special applications and requirements. The BT resin cure improves the impact resistance, adhesion, electrical properties, and processability of BMI resin, as well as the hydrolysis resistance of cyanate ester resin. If a mixture of cyanate ester, BMI, and epoxy resin is co-cured, the resulting resin cure exhibits improved processability and toughness, but its heat resistance decreases. Option 5: Other high-temperature resistant resin systems. The above has introduced the resin systems commonly used in high-heat-resistant, low-CTE copper-clad laminates. Other high-temperature resistant resin systems that have potential for use in the manufacture of such lead-free compatible copper-clad laminates include silicone polymers, polyphenylene ethers, polyphenylene sulfides, polyphenylene sulfone sulfides, aromatic polyamides, polyarylates, thermosetting liquid crystal polymers, polybenzimidazoles, benzocyclobutene resins, and polyether ether ketones. However, due to issues such as the cost of these polymers, market availability, and process feasibility, it remains challenging to use them in copper-clad laminate production. It requires the joint efforts of industry professionals to introduce these high-performance matrix resins into copper-clad laminate manufacturing as soon as possible. 2.2 Selection of Reinforcement Materials The reinforcement materials used in the manufacture of copper-clad laminates include inorganic reinforcement materials such as E, S, and Q types of glass fiber cloth and glass fiber paper, as well as high-heat-resistant organic reinforcement materials such as aromatic polyamide fibers or polyarylether fibers. However, inorganic reinforcement materials and organic reinforcement materials have different effects on the dimensional stability and CTE of the substrate material. Most inorganic materials have a low CTE, whereas organic materials generally have a high CTE, which has a significant impact on the CTE of copper-clad laminates. The CTE of some fibers is negative (such as aromatic polyamides and carbon fibers), which is very beneficial for improving the CTE in the x and y directions of copper-clad laminates. However, these fiber materials all have a two-dimensional structure and cannot improve the Z-CTE of copper-clad laminates. Z-CTE can only be adjusted by relying on the properties of the matrix resin, along with the use of filler materials and interface control techniques. 2.3 Selection of filler materials To improve the heat resistance of copper-clad laminates and reduce their coefficient of thermal expansion, a simple and effective method is to add filler materials to the resin system. Adding filler materials can not only improve the heat resistance of the sheet and reduce its thermal expansion coefficient, but also lower the production cost. Common filling materials are mostly metal or non-metal oxides or their hydrates, such as SiO2, TiO2, Al2O3, Mg(OH)2, Al(OH)3, etc. The addition of these filler materials significantly improves the heat resistance of the sheets and reduces their thermal expansion coefficient. Fillers containing whiskers are particularly effective in reducing the thermal expansion coefficient of the sheets, especially along the Z-z axis. However, special attention should be paid to the effect of the dehydration temperature of oxide or hydroxide hydrates on the sheet material. Filling materials with a dehydration temperature below 300°C should be baked before use; otherwise, moisture introduced into the board may cause it to crack. The amount of filler added is generally 10% to 30% of the matrix resin. 2.4 Manufacturing Process Technology and Issues to Be Noted 2.4.1 Resin Synthesis Process ⑴ Determination of the resin system formula First, based on the composition of the system, identify the types and quantities of active groups present in each component, as well as the type of reactions between these active groups and their reactivity. The theoretical amounts of each component are calculated based on their chemical reaction equations, and then the ratio of these components is determined using the experimental results. ⑵ Determination of reaction conditions: Based on factors such as the type of reaction between the various components in the system, their reactivity, and the reaction mechanism, the method and order of adding reactants are determined, as well as whether the reaction occurs in one step or in multiple steps. Subsequently, the temperature, time, and other conditions for the reaction are determined using reaction thermodynamics, reaction kinetics, and experimental results. ⑶ Selection of the solvent system: Solvents with similar solubility parameters are chosen based on those of the various components in the system. It is preferable to use a composite solvent system with identical or similar solubility parameters, as this allows for the creation of a certain vaporization gradient during the impregnation process, which facilitates control over this process and improves the quality of the semi-solid product. ⑷ The addition of filler materials: To improve the heat resistance of sheets and reduce properties such as CTE, as well as to lower production costs, various filler materials are often added to the resin system. Before adding the filler material, it must first be baked to remove the water absorbed by the filler, its volatile components, and some of the crystalline water. The baked filler is then subjected to coupling, coating, or grafting treatment. It is then added to the system in a certain manner, and can be used only after mixing well. 2.4.2 Impregnation Process The impregnation process in the manufacturing of copper-clad laminates employs reaction-chain growth impregnation technology, which is a type of prepreg process. The reaction chain growth impregnation technique combines the features of solution impregnation and melt impregnation, and is a type of prepreg technique used in composite materials. The characteristics of the reaction chain growth impregnation technique are as follows: First, the matrix component materials are synthesized into low-molecular-weight prepolymers (Stage A). These prepolymers have low melt viscosity and solution viscosity, which facilitates wetting and impregnation of fibers. Once the impregnated fibers are placed in an oven, the solvent evaporates under the influence of temperature, triggering the polymerization reaction of the prepolymers. The prepolymers then begin to undergo chain growth rapidly, resulting in an increase in their molecular weight. This process is controlled so that it reaches Stage B, thereby endowing the prepreg or semi-cured sheet with sufficient toughness and other desired properties. The following points should be considered in the impregnation process: depending on the matrix resin, appropriate process parameters must be used (such as resin temperature, impregnation temperature, speed, temperature distribution, etc.); factors such as single-coating prepreg, siphon time, impregnation time, the method of resin injection, flow direction, and circulation mode also play a role. These methods are employed to improve the interfacial structure and bonding condition between the matrix resin and the reinforcement, to enhance the quality of the prepreg, and ultimately to improve the overall performance of the copper-clad plate. 2.4.3 Heat Pressing Process The heat pressing process involves taking the semi-cured prepreg in stage B, laminating it with copper, and then using a heat press to apply high temperature and pressure in order to produce the final product – the copper-clad plate. The quality of control over this manufacturing process has a direct impact on the performance and quality of the final product. Composites composed of fibers and matrix resin have structural characteristics such as multi-layered structure, anisotropy, heterogeneity, and weak interlayer properties. The hot pressing process is the process of transforming the primary structure of a composite material (i.e., the single-layer material composed of matrix resin and reinforcing materials) into a secondary structure (i.e., a laminate formed by laminating these single-layer materials). The properties of the primary structure of composite materials depend on the properties, shape, distribution, and content of each component, as well as the interfacial properties. The properties of the secondary structure depend on the properties of the individual layers and the geometric arrangement of those layers (i.e., the thickness of each layer, the direction in which they are laid, the order in which they are arranged, as well as factors such as wetting, diffusion, penetration between layers or at interfaces, interfacial cross-linking reactions, and the strength of interfacial bonding). From a macro perspective, the hot-pressing process involves laminating and hot-pressing the prepreg and copper foil to transition them from stage B to stage C, thereby completing the production of the product. The hot-pressing process involves multiple interfaces between the copper foil and the prepreg, as well as between the prepregs themselves. The structural characteristics of the laminated material result in weak interlayer properties. This will affect various properties of the copper-clad plate, particularly peel strength, solderability, heat shock resistance, thermal delamination time (T288, T300), coefficient of thermal expansion, dimensional stability, flatness, interlayer shear strength, and interlayer tensile strength. Therefore, this process must be handled with care. Techniques such as vacuum hot pressing and whisker-oriented piercing, along with the proper design of various process parameters (pressure, temperature, time), as well as the control of melting time and flow window, are all aimed at enhancing or improving wetting, diffusion, penetration, cross-linking reactions, interface structure, interfacial bonding conditions, and overall performance between layers and at interfaces. Thereby **improving the overall comprehensive performance of the copper-clad plate. 3 Summary This article provides an overview of the design principles, basic design concepts, and design process for lead-free compatible copper-clad laminates ； It introduces the selection principles for raw materials, matrix resins, and reinforcing materials in composite material design, as well as the interface control techniques in the manufacturing process of copper-clad laminates ； It provides a more detailed introduction to the design and manufacturing techniques of lead-free compatible copper-clad laminates, as well as the key technologies in their production process and the issues that need attention. References: Zhu Datong, “A Review of Japanese Innovations in Impregnation Processing Technologies and Equipment (Part 1),” Printed Circuit Information, September 2007. 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