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When we need to make automotive circuit boards, we often talk about the FR-4 materials used, but today the editor of automotive circuit boards realizes that we forgive the FR-4 that we often choose, it is not a material name.
The "FR-4" we often refer to is the code name of a kind of flame-resistant material grade. It represents a material specification that the resin material must be able to extinguish by itself after burning. It is not a material name, but a kind of material. Material grade, so there are many types of FR-4 grade materials used in general circuit boards, but most of them are made of so-called Tera-Function epoxy resin with filler (Filler) and glass fiber The composite material made.
Flexible Printed Circuit Board, abbreviated as FPC, is also called flexible printed circuit board, or flexible printed circuit board. The flexible printed circuit board is a product that is designed and manufactured on a flexible substrate by means of printing.
There are two main types of printed circuit board substrates: organic substrate materials and inorganic substrate materials, and organic substrate materials are the most used. PCB substrates used for different layers are also different. For example, 3-4 layer boards need to use prefabricated composite materials, and double-sided boards mostly use glass-epoxy materials.
When choosing a sheet, we need to consider the impact of SMT
In the process of lead-free electronic assembly, as the temperature rises, the degree of bending of the printed circuit board when heated is increased. Therefore, it is required to use a board with a small degree of bending in SMT, such as FR-4 type substrate.
Since the expansion and contraction stress of the substrate after heating affects the components, it will cause the electrode to peel off and reduce the reliability. Therefore, the material expansion coefficient should be paid attention to when selecting the material, especially when the component is larger than 3.2*1.6mm. PCB used in surface assembly technology requires high thermal conductivity, excellent heat resistance (150 degree Celsius, 60min) and solderability (260 degree Celsius, 10s), high copper foil adhesion strength (1.5*104Pa or more) and bending strength (25 *104Pa), high conductivity and small dielectric constant, good punchability (accuracy ±0.02mm) and compatibility with cleaning agents, in addition, the appearance is required to be smooth and flat, without warpage, cracks, scars, and rust spots.
PCB thickness selection
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 double-sided boards with gold fingers, and 1.8mm and 3.0mm are non-standard sizes.
From the perspective of production, the size of the printed circuit board should not be less than 250*200mm, and the ideal size is generally (250～350mm)*(200*250mm). For PCBs with long sides less than 125mm or wide sides less than 100mm, Easy to adopt the way of jigsaw puzzle.
The surface mount 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 below 0.065%. It is divided into 3 types according to metal materials, as shown by typical PCB boards; 3 types according to structural softness and hardness, and electronic plug-ins are also more advanced, miniaturized, SMD and more complicated. develop. The electronic plug-in is installed on the circuit board through the pins and the pins are soldered on the other side. This technology is called THT (Through Hole Technology) plug-in technology. In this way, a hole must be drilled for each pin on the PCB circuit board, which indicates the typical application mode of the PCB.
