Circuit breaker selection principles

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Circuit breaker selection principles [Copy link]

Shenzhen Kaifei Technology Co., Ltd. Huazhu Wu

New electronic products represented by microcomputer equipment continue to emerge. Their miniaturization, thin-walling and electromagnetic interference (EMI) shielding technology, as well as the progress in the production of printed circuit boards (PCBs), have promoted the selection and consumption of resins for electronic component products and led to major changes, and began to re-evaluate the selection of resins, including connectors, bobbins, switches, capacitors, resistors and printed circuit boards. Mobile electronic devices, as the fastest growing part of the electronics industry, have an increasing demand for plastic electronic components, among which the requirements for higher thermal impedance and improved impact strength are the most important. By 2003, the total consumption of resins for electronic components in the world will reach 400,000 tons, with an average annual growth of 4.8%. The resins consumed by electronic components include a series of engineering resins, mainly nylon and thermoplastic polyester in terms of quantity. However, if compared by value, high-performance resins such as polyphenylene sulfide (PPS), polyimide (PI) and liquid crystal polymer (LCP) play an important role in the market. Engineering thermoplastics (ETP) have an advantage in the market for molded electronic components, where connectors are the most important. The consumption of thermoplastics in electronic components is expected to grow at an average annual rate of 5.9%, reaching 150,000 tons by 2003. In terms of thermosetting materials, epoxy resin has two largest applications-PCB sheets and as packaging materials, accounting for 56% of the entire thermosetting resin market. The consumption of thermosetting materials is expected to grow at an average annual rate of 4%, reaching 250,000 tons by 2003. Electronic connectors With the advancement of technology, the product update cycle of printed circuit boards and other electronic devices is getting shorter and shorter, and some have been as short as half a year to have a new generation of products. The development trend of connectors is thinner, longer, and more precise. For example, the new design and development of the semiconductor industry has led to the increase of functions of electronic devices on chips or circuit boards, which requires the production of longer, more compact, and more precise connectors. The connector spacing has also been reduced from an average of 2.5mm to 1.2mm, or even 0.8mm, the thickness is as low as 1.3mm, the flatness is 0.13mm, and it must have good bending strength, dimensional stability and electrical insulation properties. A new process for assembling electronic devices is surface mounting technology (SMT), which uses automated operation at high temperatures to complete the assembly, requiring the material to have higher heat resistance and dimensional stability. At present, surface mounting technology has accounted for 25% of the electronic device assembly technology market, and it will increase to 40%-50% by 2000. Surface mounting technology uses vapor phase welding and infrared reflow soldering, and requires welding at 250°C for 5 seconds. In addition to heat resistance, the material must also withstand the erosion of the solvent cleaning system. As connectors are becoming more and more miniaturized and refined, the fluidity of the plastic and the dimensional stability after molding must be good, so that the parts have no depressions and burrs, and still have good rigidity, toughness, and no warping on very thin sections, to ensure that the flatness of the connector reaches 0.13mm. Thermosetting plastics for connectors include phenolic, polydiallyl phthalate (DAP), epoxy resin and unsaturated polyester resin; thermoplastics include PA (polyamine) 46, PA612, PA66, PBT, PET, PCT (polyethylene cyclohexyl terephthalate), LCP, PPS, PSF (polyalkali), PEI (polyether imine), PES (polyether), PAS (polyarylether), PAE (polyarylether), etc. Hoechst of Germany has produced a modified PPS, the trade name is Fortron 1140 L7, which is dedicated to surface mounting technology connectors. It shortens the molding cycle by 50% and improves fluidity by 50% compared with general PPS. It can add 40% glass fiber reinforcement to form thin-walled parts with complex structures and longer connectors. Its molding pressure can be reduced by 40% compared with general PPS, which reduces the stress in the mold and reduces the deformation of the product. The company produces a new type of liquid crystal polymer called Vectra E130. Compared with general LCP, it can reduce the temperature by 50% and the molding pressure by 50% when molding an SMT coil-shaped coil skeleton, and the molding cycle can be shortened. This liquid crystal polymer can be used to mold thin-walled, small and complex electronic components and connectors without burrs. When it comes to competition between resins, it is actually in terms of engineering thermoplastics. Because all the engineering thermoplastics involved regard connectors as the main market, the competition is quite fierce. Printed Circuit Board Printed Circuit Board (PCB) is made by pressing copper foil on an insulating dielectric substrate. The substrate can be made of reinforcing materials such as paper, cloth, and glass fiber fabrics impregnated with liquid resins-phenolic, epoxy, polyester, polyimide, polytetrafluoroethylene emulsion, etc. After drying, the sheets are cut and stacked according to certain size requirements, and the surface is coated with copper foil and laminated to form a copper foil board. About 75% of the resin used for PCB substrates in the United States and Western Europe is brominated epoxy resin, which uses acetone as a solvent. The solid is a mixture of tetrabromobisphenol A and epoxy resin. Bromine is added to act as a flame retardant, and the bromine content is about 20%. It can also be made by adding tetrabromobisphenol A to pure epoxy resin. The miniaturization and high performance of household appliances require the use of integrated circuits with finer printed circuit spacing, with the circuit spacing narrowed to less than 0.4mm. In camera-type video tape recorders (VTRs) and portable televisions, the adoption rate of surface integration mounting technology has reached 80%-100%. This high-density printed circuit substrate often uses 4-7 layers of multi-layer technology, and the resin used has also changed from phenolic and epoxy to polyester, polyetherimide, fluororesin and other high-temperature resistant plastics. The integrated circuit boards of computers, televisions and radios are required to withstand various tests without failure in a wide temperature range of -100℃ to 160℃. Polystyrene (PSU) is an ideal material for such circuit boards because polystyrene has excellent dielectric properties at high frequencies, as well as heat resistance, acid and alkali resistance and electroplating properties. Packaging materials Electronic packaging is the process of combining semiconductor chips together to form a semiconductor-based electronic functional block device, which can be divided into chip packaging and component packaging. Chip packaging is the process of installing the chip on a carrier, or on a circuit board or component, and the carrier is usually made of plastic film. Circuit board packaging is the process of chemical etching or copper plating on a printed circuit board with epoxy resin as the substrate. Chip packaging and circuit board packaging are generally used in low- and medium-end products, while component packaging is required in high-performance computers. It is a device that packages multiple high-performance integrated circuits into an integral device through multi-layer ceramic technology to facilitate heat dissipation and reduce delays in signal transmission. Commonly used printed circuit boards are made of glass fiber reinforced epoxy resin laminates. Its disadvantages are poor thermal stability and large linear expansion coefficient. However, the basic requirement for integrated circuit packaging materials is that it has low thermal stress on electronic components, so it should be achieved through polymer alloys modified by epoxy and silicone. Carboxyl groups are introduced into silicone resin to improve its affinity with the epoxy resin interface to obtain microphase separation polymer alloys with very small dispersed particles. The diameter of the dispersed particles of silicone resin can be as small as 0.1μm or less, and the internal stress can be significantly reduced. In addition, if printed circuit boards are made of glass fiber/polyimide or aromatic polyimide fiber/epoxy resin, the thermal stability can be significantly improved without reducing its linear expansion coefficient. Therefore, two distinct markets have been formed-high-performance ETP required for electronic parts molding, and thermosetting materials used for PCB and packaging materials. Because ETP is rarely used in PCB sheets and packaging materials, and only a very small amount of thermosetting materials are used in molding electronic components, there is very little cross-application between the two. ( http://www.newmaker.com )