In this section, we will discuss various materials and layers that help us manufacture PCB boards.
Dielectric substrate material
The material sandwiched between copper layers is called a dielectric material. This material can be further divided into core and prepreg. As mentioned earlier, the most commonly used dielectric material is FR4, which is resin impregnated glass fiber. Most PCB manufacturers use FR-4 as the default substrate material.
Solder mask
The solder mask layer is mainly used to protect the copper layer from corrosion caused by exposure to the external environment. The solder mask layer can also guide the solder to move along the copper pad.
core
The wire core consists of two copper foils and an insulation layer in the middle. Copper is used for conductivity, while insulation layers are used for mechanical support and electrical insulation.
Prepreg
In PCB board manufacturing, prepreg is often mentioned. For multi-layer PCBs, multiple core boards can be connected together. This is a specific use of prepreg, but unlike core boards, prepreg is softer and more flexible. It is made of uncured resin and glass woven fabric. PCB manufacturers place pre impregnated materials between the core board layers and place them under specified temperature and pressure, and the pre impregnated materials will bond the core boards together. After this curing process, the core board and prepreg are almost indistinguishable.
Copper foil
Use layout tools to draw copper wires and pads on each layer, but PCB manufacturers actually start from the complete copper layer. Unnecessary copper in the design is etched away. Copper pads used for surface mount still require surface treatment because copper is now easily oxidized.
through-hole
As mentioned in the previous sections, the layers are insulated from each other, so a structure is needed to connect the layers. This can be achieved by drilling a copper plated hole to connect the layers. There are also various types of through holes, depending on the design and complexity of the equipment:
Through hole:The most popular and inexpensive method is to connect one layer to another through a through-hole.
Blind:The through-hole connects the top or bottom to the inner layer, but does not pass through all layers.
Buried:This through-hole does not extend to the top or bottom layer as it only connects to the internal layer.
Microchannel:Very small through holes drilled by laser are mainly used for small spacing and high-density equipment.
Due to the need for additional steps such as drilling and copper plating, the manufacturing cost of PCB is highly dependent on the number of vias.
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