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Printed circuit board base material selection and main categories

Release Date:2020-01-08

1.The FR-4 we often choose is not the name of a material

We often refer to "FR-4" as a code for a class of flame-resistant materials. It represents a material specification in which a resin material must be able to extinguish itself after being burned. Material grade, so currently there are many types of FR-4 grade materials used in general circuit boards, but most of them are so-called Tera-Function epoxy resins plus fillers and glass fiber Made of composite materials.
For example, the FR-4 water-green glass fiber board and black glass fiber board made by our family now have high temperature resistance, insulation, and flame retardant functions. Therefore, when choosing materials, you must figure out what characteristics of the materials you need to achieve. So that you can buy the products you need
Flexible printed circuit board (Flexible Printed Circuit Board, FPC for short) is also called flexible printed circuit board, or flexible printed circuit board. The flexible printed circuit board is a product in which a circuit pattern is designed and produced on a flexible substrate in a printed manner.
There are two main types of printed circuit board substrates: organic substrate materials and inorganic substrate materials. Organic substrate materials are the most used. The PCB substrates used are different for different layers. For example, prefabricated composite materials are used for 3 to 4 layer boards, and glass-epoxy materials are mostly used for double-sided boards.

2. When choosing a plate, we need to consider the impact of SMT

During lead-free electronics assembly, due to the temperature rise, the degree of bending of the printed circuit board increases when heated. Therefore, it is required in SMT to use a plate with less bending, such as FR-4 and other types of substrates. Due to the influence of the expansion and contraction stress of the substrate on the element, it will cause electrode peeling and 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) and solderability (260 ° C, 10s), high copper foil adhesive strength (1.5 × 104Pa or more) and flexural strength (25 × 104Pa), high electrical conductivity and small dielectric constant, good blankability (accuracy ± 0.02mm), and compatibility with cleaning agents. In addition, the appearance must be smooth and flat, and no warpage, cracks, scars, rust spots, etc. should occur.

3.PCB thickness selection in PCB fabrication and assembly

The thickness of the printed circuit board is 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 and 1.5 The PCB with a thickness of mm is used for the design of the double-panel with gold fingers. 1.8mm and 3.0mm are non-standard sizes. Printed circuit board size from the production point of view, the minimum single board should not be less than 250 × 200mm, generally the ideal size is (250 ~ 350mm) × (200 × 250mm), for PCBs with long sides less than 125mm or wide sides less than 100mm, easy Use the way of puzzle. The surface assembly technology stipulates the bending amount of the substrate with a thickness of 1.6mm as upper warpage ≤0.5mm and 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 and hard structure. Electronic plug-ins are also developing towards high pin count, miniaturization, SMD, and complexity. . The electronic plug is mounted on the circuit board through pins and the pins are soldered to 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.

4.Drilling in circuit board manufacturing

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 and 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, and 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 time of the hole also takes the longest. The accuracy of the hole location and the quality of the hole wall directly affect the subsequent metallization and placement of the hole, and also directly affect the printed circuit. Board processing quality and processing cost Principle, structure and function of NC drilling machine The common methods of drilling on circuit boards are NC mechanical drilling method and laser drilling method. At present, mechanical drilling method is most used.
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