What we often refer to is "FR-4 Fiber Class Material PCB Board" is a code name for the grade of fire-resistant materials. It represents a material specification that the resin material must be able to extinguish itself after being burned. 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 at present, but most of them are made of so-called Tera-Function epoxy resin plus filler (Filler) and glass fiber The composite material made.
Flexible printed circuit board (Flexible Printed Circuit Board, abbreviated 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. The PCB substrates used are different for different layers. For example, 3 to 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 lead-free electronic assembly process, due to the increase in temperature, 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℃, 60min) and solderability (260℃, 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 warping, cracks, scars and rust spots, etc.
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 Using jigsaw method.
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
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