Used for PCB substrate varieties are broadly divided into two categories, namely, organic substrate materials and inorganic substrate materials. Inorganic substrates are mainly ceramic plates and enamel-coated steel substrates. Organic substrate materials are reinforcing materials such as fiberglass cloth (fiber paper, glass felt, etc.), soaked in resin binder, through drying into a blank, and then covered with copper foil, made of high temperature and high pressure.
This type of substrate, known as copper-clad laminate (CCL), commonly known as copper-clad laminate, is the main material for the manufacture of PCB.CCL has many varieties, generally according to the board's reinforcing materials, can be divided into: paper-based, fiberglass cloth-based, composite base (CEM series), laminated multilayer base and special materials based on the (ceramics, metal-core based on the) five categories. If classified according to the different resin adhesives used in the board, the common paper-based CCL are: phenolic resin (XPC, XXXPC, FR-1, FR-2, etc.), epoxy resin (FR-3), polyester resin and other types. Common fiberglass cloth-based CCLs are epoxy resins (FR-4, FR-5), which are currently the most widely used type of fiberglass cloth-based. There are also other speciality resins (with fiberglass cloth, polybasic amide fibers, nonwoven fabrics, etc. as additional materials): bismaleimide-modified triazine resins (BT), polyimide resins (PI), diphenylene ether resins (PPO), maleic anhydride imide-styrene resins (MS), polycyanate resins, polyolefin resins, polyolefin resins, etc. CCLs are categorized by their performance and are divided into general performance CCLs, low dielectric constant CCLs, high heat resistance CCLs (generally above 150°C for boards), and low coefficient of thermal expansion CCLs (generally used on encapsulated substrates).
If the substrate material according to the rigid and flexible, can be divided into rigid CCL and flexible CCL. table 8-4 indicates the performance of various substrate materials. The glass transition temperature Tg and the coefficient of thermal expansion CTE are important parameters. In general, Tg must be greater than the circuit operating temperature and the maximum temperature in the production process, while CTE should be as small and consistent as possible.
Ceramic Substrate Ceramic circuit substrate substrate material is 96% alumina, in the case of the requirement of high strength of the substrate, 99% pure alumina material can be used. However, high purity alumina is difficult to process and has a low yield, so the price of using pure alumina is high. Beryllium oxide is also a ceramic substrate material, it is a metal oxide, with good electrical insulation properties and excellent thermal conductivity, can be used as a substrate for high power density circuits, but in the processing of the dust generated is harmful to the human body. Ceramic circuit boards are mainly used for thick, thin-film hybrid integrated circuits, multi-chip micro-assembly circuits, which has the advantages of organic materials circuit boards can not be compared. For example, the CTE of the ceramic circuit board can match the CTE of the LCCC shell, so the assembly of LCCC devices will have good solder joint reliability.
In addition, ceramic substrates are suitable for vacuum evaporation processes because they do not release large amounts of adsorbed gases that can cause a decrease in vacuum even when heated. In addition, the ceramic substrate also has high temperature resistance, good surface finish, high chemical stability, is thin, thick film hybrid circuits and multi-chip micro-assembly circuits preferred circuit substrate. However, it is difficult to process into a large and flat substrate, and can not be made into a multi-block combination of stamp plate structure to adapt to the needs of automated production. In addition, the ceramic material, because of its high dielectric constant, it is not suitable for high-speed circuit boards, and the price is the general PCB can not afford.
Epoxy glass fiber circuit board this circuit board consists of epoxy resin and glass fibers, which combines the strength of glass fibers and epoxy resin toughness advantages, so it has good strength and ductility. With it that can produce single-sided PCB, can also produce double-sided and multi-layer PCB. epoxy glass fiber circuit board in the production, the first epoxy resin penetration into the glass fiber cloth made of laminate.
At the same time, other chemicals are added, such as curing agents, stabilizers, anti-flammable agents, adhesives and so on. In the laminate on one side or both sides of the bonded copper foil made of copper-coated epoxy fiberglass laminate as the raw material for printed circuit boards. The types of laminates commonly used at present are as follows:
1. G-10 and G-11 laminates they are epoxy fiberglass laminates, do not contain flame retardant, can be drilled with drilling machine but not allowed to be punched with punching machine. the performance of G-10 is very similar to FR-4 laminates, while G-11 can withstand higher working temperature. 2. FR series laminates they all contain flame retardant, and thus are named "FR". ".
（1） FR-1 Laminate. Phenolic paper base sheet, this substrate is commonly known as Bakelite.
(2) FR-2 Laminate. It is similar to XXXPC and is a paper-based phenolic resin laminate that can only be punched with a punch, not drilled with a drill press.
(3) FR-3 Laminate. Paper-based epoxy resin laminate that can be punched at room temperature.
(4) FR-4 Laminate. Epoxy fiberglass laminate, which is extremely similar to G-10 laminate, has good electrical properties and processing characteristics, and can be made into multilayer boards. It is widely used in industrial products.
(5) FR-5 laminate. It has similar properties to FR-4, but can maintain good strength and electrical properties at higher temperatures.
(6) FR-6 Laminate. Polyester resin fiberglass laminate. The above laminates, commonly used G-10 and FR-4 for multi-layer printed circuit boards, relatively inexpensive, and can be drilled using a drill press, easy to automate the production.
non-epoxy resin laminates such laminates are mainly polyimide resin fiberglass laminates, Teflon fiberglass laminates, phenolic resin paper-based laminates and so on.
(1)polyimide resin fiberglass laminate. It can be used as a rigid or flexible circuit substrate material, and its strength and stability at high temperatures are superior to FR-4 laminates, which are commonly used in highly reliable military products.
(2)GX and GT laminates. They are polytetrafluoroethylene glass fiber laminates, the dielectric properties of these materials can be controlled, used in products with stringent dielectric constant requirements, while the dielectric properties of GX is better than GT, can be used in high-frequency circuits.
(3) XXXP and XXXPC laminates. They are phenolic resin paper base plate, can only be punched can not be drilled, these laminates are only used for single-sided and double-sided printed circuit boards, and can not be used as raw materials for multilayer printed circuit boards. Because it is inexpensive, they are widely used as circuit substrate materials in civilian electronics. For each type of laminate, they have their own maximum continuous operating temperature, if the operating temperature exceeds this temperature value, the electrical and mechanical properties of the laminate to deteriorate significantly, and even affect the function of the assembly. Table 8-5 lists the maximum continuous temperature of commonly used circuit board materials. From the table can be seen in the polyimide's maximum continuous
The highest working temperature, it belongs to the high-temperature laminate category. Table 8-5 The highest continuous temperature of commonly used circuit substrate materials 3.CCL commonly used character code in the national standard GB/T 4721-92, provides for the CCL product model with a few letters of the alphabet and two Arabic numerals. The first letter C indicates copper foil; the second and third two letters indicate the resin used in the base material; PE: phenolic EP: epoxy UP: polyester SI: silicone TF: polytetrafluoroethylene PI: polyimide the fourth and fifth letters indicate that the reinforcing material; CP: cellulose/fiber paper GC: non-alkali glass cloth GM: column alkali glass fiber felt AC: Aromatic Polyamide Fiber Cloth AM: Aromatic Polyamide Fiber If cellulose paper is used as the reinforcing material, and alkali-free glass cloth is attached on both surfaces, "G" is added after CP. At the end of the letter with a short horizontal line connected to two numbers, indicating that the same kind of different properties of the product number. With flame retardant CCL in the number after the letter "F".
CCL commonly used character code in the national standard GB / T 4721-92, the provisions of the CCL product model with a few letters and two Arabic numerals. The first letter C indicates copper foil; the second and third two letters indicate the resin used in the base material; PE: phenolic EP: epoxy UP: polyester SI: silicone TF: polytetrafluoroethylene PI: polyimide the fourth and fifth letters indicate the reinforcing material; CP: cellulose/fiber paper GC: non-alkali glass cloth GM: alkali glass fiber felt AC: aromatic polyamide fiber cloth AM: aromatic polyamide fiber If cellulose paper is used as the reinforcing material, and alkali-free glass cloth is attached on both surfaces, "G" is added after CP. At the end of the letter with a short horizontal line connected to two numbers, indicating that the same kind of different properties of the product number. Flame retardant CCL is indicated by adding the letter "F" after the number.
Example: CEPCP (G)-23F indicates that the epoxy paper-based two-surface glass cloth attached to the copper-clad plate, with flame retardant. 4. copper foil type and thickness of copper foil on the electrical performance of the product has a certain impact, copper foil is generally divided into two major categories of calendered and electrolytic copper foil according to the manufacturing method. Calendered copper foil requires high copper purity (generally ≥99.9%) and good elasticity, which is suitable for the manufacture of high-performance PCBs such as flexible boards, high-frequency signal boards, etc., and is indicated by the letter "W" in the product specification. Electrolytic copper foil is used in the manufacture of ordinary PCBs, the purity of copper is slightly lower than that used in the calendering method (generally 99.8%), and is indicated by the letter "E".
