A preliminary study on PCB substrate - the "three lives and all things" of copper clad laminate CCL
According to statistics, the cost of PCB substrate accounts for about 30-50% of the total cost of PCB. It is the absolute main material. "Good medicinal materials make good medicine!" Similarly, for PCB manufacturers, understanding PCB substrate will undoubtedly give them a natural and absolute advantage in responding to customer needs in the future. Only by choosing the right one can we do it right!
1: Official definition:
Copper Clad Laminate (CCL) is a plate-like material made by impregnating electronic fiberglass cloth or other reinforcing materials with resin, covering one or both sides with copper foil and hot pressing. It is referred to as copper clad laminate. Printed circuit boards of various forms and functions are selectively processed, etched, drilled and copper-plated on copper clad laminates to make different printed circuits. It mainly plays the role of interconnection, insulation and support for printed circuit boards, and has a great influence on the transmission speed, energy loss and characteristic impedance of signals in the circuit. Therefore, the performance, quality, processability in manufacturing, manufacturing level, manufacturing cost, and long-term reliability and stability of printed circuit boards depend to a large extent on copper clad laminates.
2: The substrate is the cross section of the wire.
We still start from the function of PCB to examine the PCB substrate.
The emergence of PCB is to flatten and miniaturize the complicated and three-dimensional wires/conductors. The basis of flattening must have a continuous plane-with a certain mechanical strength: electronic glass cloth or other reinforcing materials (core material). A thin layer of copper foil is glued on the core material with different resin systems (glue) and hot-pressed to solidify it. You can understand it as cutting and flattening the paint-coated wire. The core material (insulating material) is the paint, and the copper is the conductor. The paint and copper wire are separate because they are not bonded with glue (resin).
3: The so-called "three births of all things" PCB substrate, namely CCL,
in short, contains 3 parts: resin, reinforcement material, and conductive copper foil. However, the changes in each component will produce many combinations, making the issues that can be discussed about the substrate much more complicated. One of the main causes of complexity is that PCB applications are quite wide, resulting in many different requirements in terms of cost and performance, because there are multiple grading standards for PCB substrates. The three components can deduce thousands of possibilities to meet different needs. This is the so-called: three births of all things.
4: Classification of copper clad laminates:
From the perspective of hard board, according to the basic components of its core material, it can be divided into:
paper board (XPC, XXPC, XXXPC)
composite fiberboard (CEM-1, CEM-3)
glass fiberboard (FR-4)
ceramic substrate, metal substrateA: Paper copper clad laminate
A: Paper copper clad laminate
Its composition is paper + resin + copper foil.
Paper copper clad laminates are divided into: XPC-XXPC-XXXPC according to the resin they contain. X represents the resin content. The more X, the more resin content, and the better its insulation performance; P represents paper; C represents cold punching.
The disadvantages of paper copper clad laminates are: relatively poor hardness, easy to absorb moisture in a humid environment, large changes in thermal expansion under high temperature and contraction after cooling, and lower electrical performance than fiberboard. The advantage is low raw material cost. Because it is soft and can be punched, the hole processing cost in the PCB process is low.
B: Composite fiberboard
The commonly used models of this type of board are CEM-1 and CEM-3.
C is composite, E is epoxy, which is not easy to burn. The flame retardancy of this resin material is increased; M is base material.
CEM-1 is composed of: paper core + fiber cloth + epoxy resin + copper foil.
CEM-3 is composed of: glass fiber non-woven fabric (core) + glass fiber cloth (surface) + epoxy resin + copper foil.
CEM-3 contains more fiber layers than CEM-1, because it is more flame resistant, insulating, and hardness is higher than CEM-1. The cost of composite fiberboard is lower than that of glass fiberboard, which solves the problems of insufficient hardness of paperboard and difficulty in punching of fiberboard. Its disadvantage is that although the electrical performance is close to that of glass fiberboard, it still cannot completely replace FR-4 material. Only some circuit boards with low requirements can use this material instead of FR-4.
C: Fiberglass board
The structure is glass fiber cloth + resin + copper foil.
Glass fiber cloth is the common material currently used in FR-4 materials.
Its advantages are high hardness, strong fire resistance, stable electrical properties, and can be used for copper-plated hole processing.
Its disadvantage is that the main raw materials are glass fiber cloth and epoxy resin, so the cost of board production and the cost of hole processing during circuit board manufacturing are high.
Tips: I have never understood the difference between CEM-3 and FR-4. It turns out that the secret is this: glass fiber non-woven fabric and glass fiber woven fabric, there is only one word difference. (Similar to non-woven fabric/non-woven fabric and woven fabric: the difference lies in whether it is woven with warp and weft. Non-woven fabrics are slightly harder and have lower bending strength/or are easy to break. Woven fabrics are generally very soft and very strong).
D. Ceramic substrate, metal substrate
As the name implies, ceramic or metal, such as iron-based, aluminum-based, copper-based, etc., is used as the substrate of the dielectric layer.
It is mainly used in some fields with high temperature, high humidity, high conductivity, and uninterrupted continuous operation.
Due to the limited conditions, the production cost is high, and the application is not very extensive. It is mainly used in military, industrial control, and other fields with high reliability.
5: Differences in core materials of FPC soft boards
By the way, the above classifications are all for the basic components of hard boards.
In fact, the three major components of soft boards are the same: core material, resin, and copper foil.
In contrast to the core material of hard boards, the core material of hard boards is called "reinforcement material", which can be understood as requiring hardness, that is, high mechanical strength, while the core material of soft boards is relatively soft, with less filler, or part of it is directly consistent with the resin system. Currently, the more common ones such as PI, PPE, PPO, and the highly promising LCP in the future are all "core materials" of soft board FPC.
For soft boards, the resin system is more important and critical, because the core material requires softness. If the resin system is not properly matched, it will increase the hardness of the overall substrate (the resin thickness is about 2/3 of the substrate thickness, and it is coated on both the upper and lower surfaces), which runs counter to the characteristics of soft boards - soft and bendable.
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