Multilayer printed circuit boards play a crucial role in the field of printed circuit board manufacturing, particularly in high-density electronic products. This article will take an in-depth look at the substrate materials and prepregs (PP) used in multilayer printed circuit boards, highlighting their key roles and performance characteristics in the manufacturing process.
1. Substrate Materials for Multilayer Boards
1.1. Thin-core FR-4 copper-clad laminate
Thin-core FR-4 copper-clad laminate is an indispensable substrate material in the manufacture of multilayer printed circuit boards. It has the following characteristics:
- Insulation thickness: Provides electrical insulation, ensures impedance control, and enables internal potting.
- Resin Bonding: It adheres firmly to the inner blackened layer and the outer copper foil.
- Dimensional Stability: The dimensions of the inner layers are consistent across all layers, ensuring that the hole rings on each layer align with the through-holes.
- Panel Flatness: Maintain the flatness of the panel surface and minimize warping.
1.2. FR-4 prepreg
FR-4 prepreg, used as the insulating medium for the inner and outer layers of multilayer printed circuit boards, serves the following specific purposes:
- Provide the thickness of the multilayer board.
- Provides electrical insulation, including filling the gaps between the inner layers of wire.
- Control the accuracy of the characteristic impedance.
The "Prepreg" shown in the figure is a semi-cured sheet, commonly known as PP.
2. Overview of Multilayer Board Preforms
Prepregs are the primary material used in the manufacture of multilayer boards. They are thin sheets composed of resin and reinforcing materials, and their characteristics are as follows:
- Reinforcing Materials: Glass cloth is typically used, such as types 106, 1080, 2116, and 7628.
- Resin Type: Epoxy resin, dimaleimide/triazine, polyimide, etc.; the corresponding films include various grades such as FR-4, BT, and PI.
- Resin Stage: These include Class A (liquid resin), Class B (semi-cured), and Class C (fully cross-linked).
The surface of the prepreg has undergone special treatment to improve the adhesion between the glass fabric and the resin.
Substrate materials and prepregs play a crucial role in the manufacture of multilayer printed circuit boards. Understanding their performance characteristics and applications helps ensure the production of high-quality multilayer printed circuit boards that meet the demands of modern electronic products for high-density circuits.
FAQ
1. What is a thin-core FR-4 copper-clad laminate used in multilayer boards?
Thin-core FR-4 copper-clad laminate is a substrate material for multilayer printed circuit boards, offering electrical insulation and dimensional stability.
2. What is the role of prepregs in the manufacture of multilayer printed circuit boards?
Prepregs are used to provide the insulating medium for the inner and outer layers of multilayer boards and to control the accuracy of the characteristic impedance. Prepregs, also known as resin-impregnated sheets or PP sheets, consist primarily of epoxy resin and glass fiber cloth (as a reinforcing material). This thin sheet material is produced by impregnating treated electronic-grade glass fiber cloth with epoxy resin and then subjecting it to heat treatment (drying); it is one of the primary materials used in the production of multilayer printed circuit boards. It softens under heat and pressure and cures upon cooling. It meets the product requirements of most customers and is primarily used in: epoxy boards, epoxy tubes, copper-clad laminates, and carbon-crystal heating plates.
3. What are the common types of glass cloth used in multilayer boards?
Common glass cloth grades used in multilayer boards include 106, 1080, 2116, 7628, and others.
4. What is the resin stage of a prepreg?
The resin stages of prepregs include Stage A (liquid resin), Stage B (semi-cured state), and Stage C (fully cross-linked).
5. Why are prepregs needed in the manufacture of multilayer boards?
The manufacture of multilayer printed circuit boards requires prepregs to provide insulation, alignment, and characteristic impedance control, ensuring the reliability and performance of high-performance electronic products.
