Insulating laminates for electronics, also known as laminates, have a wide variety of insulating laminates, including phenolic cotton laminates, epoxy fiberglass panels, and copper clad laminates. Insulating laminates are made of two layers or laminates of organic substrate insulation laminates –
The insulating laminate is a unit in which two or more layers of resin-impregnated fibers or fabrics are laminated and heat-pressed. It can be a plate, tube, rod or other shape. Laminates can be processed into a wide range of insulation and structural components for use in motors, transformers, high and low voltage electrical appliances, electrical instrumentation and electronics. With the development of the electrical industry, high insulation. Laminated plastic products with high strength, high temperature resistance and adaptability to various environments have emerged. Copper clad laminates for printed circuits are also rapidly evolving due to the needs of the electronics industry. Chinese electrical and electronic laminates were gradually developed after liberation. China’s thermoset laminates have formed a relatively complete series.
The performance of an insulating laminate depends on the substrate and adhesive as well as the molding process. The laminates can be classified into the following two types according to their compositions, characteristics, and heat resistance.
(1) Organic substrate insulating laminates for electronics – wood pulp insulation paper, cotton fiber paper, cotton cloth, etc. as reinforcing materials. The long-term use temperature can reach 120 ° C, and synthetic fiber products have also been developed as reinforcing materials.
(2) Inorganic substrate insulating laminates for electronics – using inorganic glass fiber cloth, alkali-free glass fiber mat and the like as reinforcing materials. The long-term use temperature is 130~180 °C, even higher, depending on the binder resin. Laminate plastic articles are classified into laminates, laminates, laminates, and molded laminates by shape and use. Copper-clad laminates for printed circuits and adhesive-capacitor sleeves for capacitive bushings for high-voltage electrical appliances are two special types of laminated plastic products.
The phenolic laminated paper board has high mechanical strength, excellent moisture resistance and heat resistance, good electrical properties (poor layout), easy processing, and is widely used in electrical products. Phenolic laminated paper, cloth density of about 1.35g / cm3, half lighter than aluminum, used in aviation and other structures. Phenolic laminates are chemically resistant, resistant to organic solvents, organic acids and rare mineral acids. They are suitable for many chemical equipment and are generally not suitable for alkaline media.
Laminated paperboard can withstand sawing, drilling, turning, milling, planing, etc. No cracks and slags should be formed after processing. The thickness can be punched below 3mm, and the cold-punching type does not need heating. Hot after punching. Used for insulation parts of high and low voltage electrical appliances and electronics industry. The processing performance of the board is better than that of cardboard and glass cloth. The bonding strength and impact strength are higher than that of the paperboard, but the water absorption is large, the electrical insulation is reduced after moisture absorption, and the mold is prone to mildew, which is not suitable for use in hot and humid areas. Therefore, it is generally used as an insulating structural component of low-voltage motor appliances, such as washers, wedges, and screws. There are many kinds of glass cloth sheets, and their performances vary with the binder resin. Compared with other laminates, glass cloth boards have higher mechanical strength and heat resistance, and their bending resistance and resistance under high temperature. Although the tensile strength of Zhang and Zhang is reduced, it is still higher than that of cardboard and tape.
The melamine glass cloth has high strength, arc resistance and flame resistance, and is especially suitable for marine electrical appliances. Epoxy phenolic glass cloth board, silicone epoxy glass cloth board, diphenyl ether glass cloth board, polyimide glass cloth board, polyamine-imide glass cloth board, etc., good dielectric properties, and high It is heat resistant and flame resistant, so it is an excellent dielectric insulation board. Among them, the most widely used is the epoxy phenolic glass cloth board. Glass cloth panels are widely used in industries such as electrical, construction, chemical, electronics, aircraft, aerospace, automotive, electric vehicles and ships due to their excellent performance.
The quality problem of the laminate is a comprehensive reflection of the quality problems of the resin, sizing and pressing processes. Although pressing is the last critical step in the manufacture of laminates, the quality of the semi-finished products produced in the previous process will have a direct impact on the quality of the laminate.
Therefore, the quality problems of the laminates must be thoroughly analyzed in order to find the exact cause, and timely effective measures can be taken to improve the quality of the laminate.
(1) Surface burr This phenomenon tends to occur in thin sheets, mainly adhesive paper cloth, especially the surface material contains a small amount of glue, the soluble resin content is low, and the resin has poor fluidity. Secondly, the pressure is uneven during pressing. In some cases, the preheating time is too long and the pressure is low. Therefore, when preparing the thin sheet material, special attention should be paid to the soluble resin content of the adhesive tape cloth, and a good surface material is preferably used, and the thin plate and the thick plate are preferably pressed together to increase the elasticity of the blank to make the heat and pressure uniform. If there is only a thin plate task due to the limitation of product specifications, the pad paper should be thickened and replaced frequently. The preheating time should not be too long and the pressure should be tight. In addition, the temperature of the hot plate should not be too high when the glue is applied.
(2) The phenomenon that the surface is uneven and flawed often occurs in the rubber paper with large resin content and low solubility. Due to the small fluidity of the resin, the uneven amount of glue caused by the glue is easily reflected on the surface of the laminate. Unfair and flawed. Therefore, it is necessary to pay attention to the uniform control of the amount of glue when sizing. When stocking, pay attention to the fact that each piece of material is reversed and adjusted to 180° to compensate for the uneven amount of glue caused by the sizing, so that the surface condition can be improved.
(3) Cracking of the laminate. The cracking phenomenon mainly occurs in thick paper and cloth sheets, and cracks occur in laminates of 5 mm or more in severe cases. The epoxy phenolic glass cloth board is not easy to crack, which is because the adhesive strength of the glue is strong. The cracking of the laminate has a great relationship with the resin adhesion. When the aging material is sandwiched between the laminates, the laminate must be cracked. Therefore, the selection of the adhesive paper should be carried out, and the aging materials should be selected and cannot be mixed into the blank. . In addition, the amount of adhesive tape is too small and uneven, the pressure is too low or the pressure is too slow, and it is easy to cause cracking.
(4) The color of the middle part of the surface is dark, and the periphery is white. This is mainly because the volatile matter of the adhesive tape is large. When the preheating, the volatile matter is easy to escape, and the volatile matter in the middle is large, so the periphery is white and the middle color is deep. This can be judged to be caused by volatile matter from the low withstand voltage of the middle of the plate than the withstand voltage at the whitish edge of the plate. Therefore, the moisture absorption of the adhesive tape should be prevented, especially if the content of the soluble resin of the adhesive tape is too large, and the low molecular weight generated during the hot pressing is correspondingly increased, and this phenomenon is more serious. The test proves that the low molecular weight is more affected than the water. It has been proved that the volatiles of the adhesive tape do not produce white edges below 4%, and the preheating of 6% or less can produce no white edges or few white edges, more than 6% white edges. Big.
(5) Surface fracturing This is mainly because the resin is pressed too quickly during the flow, and the substrate is crushed. Therefore, the number of times and the pressure of the adhesive tape should not be too high when the glue is applied. The unit pressure of the epoxy phenolic glass cloth plate exceeding 7 MPa (70 kgf/cm2) will break the glass cloth.
(6) The surface area rubber reinforcing material itself has a large thickness deviation, causing uneven glue amount or lack of glue machine, resulting in excessive glue amount at a certain position of the paper cloth, uneven fluidity, and uneven heat transfer of the hot plate during preheating. The content of the soluble resin is large, and the pressure is too fast when the resin flows. Therefore, the thickness deviation of the substrate should not be too large, the glue amount of the adhesive tape should be uniform, and the content of the soluble resin should be reduced. When preparing the material, it is necessary to adjust a part of the adhesive tape to 180° upside down, and the pressurization should not be too fast when preheating. Pay attention to the exclusion of pipes and hot plate condensate.
(7) The deviation of the thickness of the laminate is large. The thickness deviation is usually thin in the middle of the edge, which is mainly caused by the unevenness of the edge of the steel sheet. Therefore, the steel plate should be kept in a safe place, and it should be used after the edge is found to be flattened. The large deviation also has a thin side phenomenon, which is mainly caused by the old side of the adhesive tape, the side being tender, or the high temperature on the side of the hot plate, the low temperature on the side, and the inclination of the hot plate. Therefore, when preparing the material, pay attention to adjust a part of the adhesive tape to 180°, and the inlet and outlet of the pipe are staggered. When preheating, pay attention to draining the hot plate and water in the pipeline to prevent the temperature of the hot plate from being high and the temperature is low. Always check the hot plate tilt and repair it in time. The thickness deviation and the thick edge of the middle part are thin, which is mainly caused by the deformation of the central depression which occurs in the hot plate for a long time. The hot plate should be repaired.
(8) Sliding out of the sheet When pressed, the adhesive tape slips out of the steel sheet, especially when the epoxy phenolic glass cloth is pressed, which is generally called “running material”. There are many reasons for the running of materials. For example, the amount of adhesive tape is too large and too tender, the amount of glue on both sides is uneven, the materials are not uniform, the loading is not correct, the pressurization is too fast and too high during preheating, and the heat plate itself is unevenly stressed. There will be a phenomenon of running materials, and running materials will cause personal equipment accidents, so be sure to pay attention to prevention. The same batch of adhesive paper cloth is used in the preparation of the materials, the glue content and the solubility are basically the same, the blanks are aligned and installed, and the temperature is gradually increased and pressurized. In case of running materials, the steam should be turned off, but keep enough pressure to observe the slipping condition, adjust it after stabilization, and then gradually increase the steam to continue pressing.
(9) Adhesive steel plate or surface oil flower is mainly caused by improper dosage of the release agent. The internal release agent such as zinc stearate, calcium, barium, oleic acid, etc. is used less, or the external release agent is wiped too much. If it is small and uneven, it will stick to the steel plate. If the amount is large or the mold release agent is not dried, the material will be easily produced. Therefore, it is necessary to strictly control the amount of the internal release agent, and it is necessary to wipe the external release agent, such as floor wax, silicone rubber, etc., the concentration of the release agent should be properly adjusted, and it should be evenly rubbed to form a thin layer, and then discharged after being dried. . In addition, the bonded steel plate is related to the surface quality of the steel plate, and the surface is poorly cleaned or insufficiently treated, and the steel plate is easily adhered. Sometimes, the work material is used as a surface material due to carelessness, and the phenomenon of sticking the steel plate may occur.
(10) The warpage of the laminate is too large. This phenomenon often occurs in 7~15mm thick cardboard. The reason for warping is very complicated, such as uneven amount of adhesive tape, temperature rise during pressing, cooling rate too fast, discharge temperature Too high, the collocation scheme is unreasonable, etc., but mainly due to internal stress. Therefore, internal stress should be minimized. For example, when heating or cooling, slowly supply steam or cold water to prevent the laminate from being hot or cold. If there is enough cooling time, it can’t be shortened arbitrarily. When the water pressure is insufficient, the time should be extended appropriately. The collocation scheme should pay attention to the uniform heating of the laminate. When preparing the material, try to adjust the adhesive paper to several times, which is good for reducing warpage.
(11) Unsatisfactory voltage withstand voltage .The main problem is that the voltage withstand voltage is mainly thin, because the voltage resistance standard of the thin plate is higher than that of the thick plate. After the heat treatment process is cancelled, the withstand voltage of the thin plate often fails to meet the standard requirements. The breakdown voltage of the thin plate has a great relationship with the volatile matter of the adhesive tape. It has been proved that when the volatiles of 3020 adhesive tape are below 4%, the withstand voltage is qualified, the volatile matter is unstable at 4.5% to 5%, and the pass rate of 5% or more is extremely high. low. Laminates with unacceptable voltages are hot-baked and generally effective, but some laminates with low voltage resistance are not acceptable for hot baking. The amount of hot baking is very large, so the adhesive tape should be stored in a dry storage and should not be damp.