Generally, PCBs can be categorized based on the reinforcement materials into five major types: paper-based, glass fiber cloth-based, composite substrates (CEM series), laminated multilayer boards, and special material substrates (ceramic, metal core, etc.).When classified according to the resin adhesives used, common paper-based CCIs include: phenolic resin (XPc, XxxPC, FR-1, FR-2, etc.), epoxy resin (FE-3), polyester resin, and various other types. The most commonly used glass fiber cloth-based CCLs are epoxy resin (FR-4, FR-5), which is currently the most widely used type of glass fiber cloth-based material.Additionally, there are other specialty resins (using glass fiber cloth, polyamide fibers, non-woven fabrics, etc. as reinforcing materials): bismaleimide modified triazine resin (BT), polyimide resin (PI), diphenyl ether resin (PPO), maleic anhydride imide-styrene resin (MS), polycyclic resin, polyolefin resin, etc. According to the flame retardant performance of CCLs, they can be divided into flame-retardant types (UL94-V0, UL94-V1) and non-flame-retardant types (UL94-HB).In the past couple of years, with increasing emphasis on environmental issues, a new type of flame-retardant CCL that does not contain bromine has emerged, which can be referred to as “green flame-retardant CCL”. With the rapid development of electronic product technology, there are higher performance requirements for CCLs. Therefore, based on the performance classification of CCLs, they can be divided into general performance CCLs, low dielectric constant CCLs, high thermal resistance CCLs (generally with a thermal resistance above 150°C), and low thermal expansion coefficient CCLs (commonly used in packaging substrates).Introduction to PCB circuit board materials: categorized by brand quality level from low to high as follows: 94HB-94VO-22F-CEM-1-CEM-3-FR-4
Detailed parameters and uses are as follows: 94HB: ordinary paperboard, not fireproof (the lowest grade material, can be punched, cannot be used for power boards) 94V0: flame-retardant paperboard (can be punched) 22F: single-sided semi-glass fiber board (can be punched) CEM-1: single-sided glass fiber board (must be drilled with a computer, cannot be punched) CEM-3: double-sided semi-glass fiber board (the lowest grade of double-sided board material, simple double-sided boards can use this material, cheaper by 5-10 yuan/m² than FR-4) FR-4: double-sided glass fiber board The classification of flame-retardant properties can be divided into four types: 94VO-V-1-V-2-94HB Prepregs: 1080=0.0712mm, 2116=0.1143mm, 7628=0.1778mm FR4 CEM-3 represent board materials, FR4 is glass fiber board, CEM3 is composite substrate Dielectric constant of PCB materials The study of the dielectric constant of PCB materials is important because the speed and integrity of signals transmitted on PCBs are affected by the dielectric constant. Therefore, this constant is crucial. Hardware personnel often overlook this parameter because the dielectric constant is determined when manufacturers use different materials to make PCB boards; for example, the dielectric constant of Shengyi’s PCB board is 3.7, while the dielectric constant of Ultrasonic PCB board is 4.2. Based on the formula for the signal output speed on PCB boards: where c is the speed of light, Er is the dielectric constant of the PCB board. According to the above formula, some common conclusions can be drawn: 6mil/ps, 6inch/ns. According to Baidu Baike’s explanation, the dielectric constant: when a dielectric is subjected to an external electric field, it generates induced charges that weaken the electric field. The ratio of the original external electric field (in vacuum) to the final electric field in the dielectric is the relative permittivity (relative permittivity or dielectric constant), also known as dielectric constant, which is frequency dependent. The dielectric constant is the product of the relative permittivity and the absolute permittivity in a vacuum. If a material with a high dielectric constant is placed in an electric field, the electric field strength will significantly decrease within the dielectric. The relative dielectric constant of an ideal conductor is infinite. Based on the dielectric constant of a substance, the polarity of polymer materials can be determined. Usually, substances with a relative dielectric constant greater than 3.6 are polar substances; those with a relative dielectric constant between 2.8 and 3.6 are weakly polar substances; and those with a relative dielectric constant less than 2.8 are non-polar substances.
Dielectric Constant of FR4 Materials
The dielectric constant (Dk, ε, Er) determines the speed at which electrical signals propagate through the medium. The speed of electrical signals is inversely proportional to the square root of the dielectric constant. The lower the dielectric constant, the faster the signal transmission speed. To illustrate, it’s like running on a beach where the water depth covers your ankles; the viscosity of the water represents the dielectric constant. The stickier the water, the higher the dielectric constant, and the slower you run. The dielectric constant is not very easy to measure or define; it is related not only to the properties of the medium itself but also to the testing methods, testing frequency, and the state of the material before and during testing. The dielectric constant can also vary with temperature changes; some special materials are developed with temperature factors in mind. Humidity is also an important factor affecting the dielectric constant, as the dielectric constant of water is 70, and even a small amount of moisture can cause significant changes. Dielectric loss of FR4 materials: The energy loss caused by the dielectric conductivity and the lagging effect of dielectric polarization under the action of an electric field. It is also called dielectric loss, abbreviated as dielectric loss. Under the action of an alternating electric field, the angle between the current phasor and the voltage phasor in the dielectric (the power factor angle Φ) is called the dielectric loss angle. The dielectric loss of FR4 materials is generally around 0.02, and it increases with frequency. TG value of FR4 materials: also known as the glass transition temperature, generally at 130°C, 140°C, 150°C, 170°C. Common Thickness of FR4 Materials Commonly used thicknesses: 0.3mm, 0.4mm, 0.5mm, 0.6mm, 0.8mm, 1.0mm, 1.2mm, 1.5mm, 1.6mm, 1.8mm, 2.0mm. The thickness tolerance of the board depends on the manufacturing capabilities of the board factory. Common copper thickness for FR4 copper-clad boards: 0.5 oz, 1 oz, 2 oz, other copper thicknesses are also available, and need to be confirmed with PCB manufacturers.
Source: PCB Electronic Circuit Technology, PCB World
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