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Classification selection of PCB materials

2020-01-02 14:28:37

There are two main types of printed circuit board substrates: organic substrate materials inorganic substrate materials. Organic substrate materials are the most used. The PCB base materials used are different for different layers. For example, prefabricated composite materials are used for 3 to 4 layer boards, glass-epoxy materials are mostly used for double-sided boards.

First, when choosing a plate, we need to consider the impact of SMT

During lead-free electronics assembly, as the temperature rises, the degree of bending of the printed circuit board increases when heated. Therefore, in SMT, it is required to use as small as possible the bending plate, such as FR-4 other types of substrates. Due to the influence of the expansion contraction stress of the substrate on the element, it will cause electrode peeling reduce reliability. Therefore, pay attention to the material expansion coefficient when selecting materials, especially when the element is larger than 3.2 × 1.6mm. PCBs used in surface assembly technology require high thermal conductivity, excellent heat resistance (150 ° C, 60min) solderability (260 ° C, 10s), high copper foil bonding strength (above 1.5 × 104Pa) flexural strength (25 × 104Pa), high electrical conductivity small dielectric constant, good punchability (accuracy ± 0.02mm), compatibility with cleaning agents. In addition, the appearance must be smooth flat, no warpage, cracks, scars, rust spots, etc. should occur. pcb customization


Choice of PCB thickness

Printed circuit board thicknesses are 0.5mm, 0.7mm, 0.8mm, 1mm, 1.5mm, 1.6mm, (1.8mm), 2.7mm, (3.0mm), 3.2mm, 4.0mm, 6.4mm, of which 0.7mm 1.5 The PCB with a thickness of mm is used for the design of the double-panel with gold fingers. 1.8mm 3.0mm are non-standard sizes. Printed circuit board size the production point of view, the minimum single board should be less than 250 × 200mm, generally the ideal size is (250 ~ 350mm) × (200 × 250mm). For PCBs with long sides less than 125mm wide sides less than 100mm, Use the way of puzzle. The surface assembly technology specifies the bending amount of the substrate with a thickness of 1.6mm as upper warpage ≤0.5mm lower warpage ≤1.2mm. Generally, the allowable bending rate is less than 0.065%. It is divided into 3 types according to metal materials, as shown in typical PCBs. It is divided into 3 types according to soft hard structure. Electronic plug-ins are also developing towards high pin count, miniaturization, SMD, complexity. . The electronic plug is mounted on the circuit board through pins the pins are soldered on the other side. This technology is called THT (ThroughHoleTechnology) plug-in technology. In this way, a hole is to be drilled for each pin on the PCB, which illustrates the typical application of the PCB.

Third, drilling

With the rapid development of SMT chip technology, multi-layer circuit boards need to be electrically connected. This is ensured by electroplating after drilling, which requires various drilling equipment. In order to meet the above requirements, at present, PCB numerical control drilling equipment with different performances are introduced at home abroad. The production process of printed circuit boards is a complex process, which involves a wide range of processes. The main fields involved are photochemistry, electrochemistry, thermochemistry. There are also many process steps involved in the manufacturing process. The multilayer wiring board is taken as an example to explain the processing steps. Drilling is a very important process in the entire process, the processing of the hole takes the longest time. The accuracy of the hole location the quality of the hole wall directly affect the subsequent metallization placement of the hole, also directly affect the printed circuit. Board processing quality processing cost Principle, structure function of NC drilling machine The common methods of drilling on circuit boards are NC mechanical drilling method laser drilling method. At present, mechanical drilling method is used the most. Circuit board manufacturer

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