Four-Layer PCB Ground Plane Design for Cost Reduction
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Solution Overview
Problem
Existing six-layer HDI printed circuit boards have high fabrication costs due to excessive processes and numerous material layers, making them difficult to thin while maintaining insulation strength, which increases the overall cost and thickness of the board.
Innovation Solution
A four-layer printed circuit board design with surface layers and two inner layers, where the surface layers are primarily ground copper sheets interconnected through vias, and the inner layers are primary wiring layers with a significant distance between them, reducing signal crosstalk and fabrication costs while maintaining performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a six-layer HDI board structure is used to ensure signal quality and insulation strength, then the reliability and signal quality are improved, but the fabrication cost increases and the board thickness cannot be reduced
Solution Approach 1:
The patent extracts and removes unnecessary intermediate insulation layers from the traditional six-layer HDI structure, simplifying it to a four-layer board. By taking out the redundant layers while retaining the essential ground copper sheets and signal transmission functions, the fabrication cost and process complexity are reduced without compromising signal quality
Solution Approach 2:
The surface ground copper sheets in the four-layer board serve multiple functions: they provide reference ground planes for signal layers, act as shielding layers for electromagnetic interference, and maintain insulation strength. This multi-functionality allows the simplified four-layer structure to replace the more complex six-layer structure
2Device complexity
If the number of layers is reduced from six to four to lower fabrication cost, then the fabrication cost and process cycle are improved, but the insulation strength between layers may be compromised
Solution Approach 1:
The patent applies local quality by using large-area ground copper sheets at the surface layers that provide enhanced local insulation strength and electromagnetic shielding. These ground sheets are strategically positioned to ensure adequate insulation between signal layers while maintaining the simplified four-layer structure
Solution Approach 2:
The invention changes the structural parameters by increasing the area of ground copper sheets and optimizing their positioning in the four-layer configuration. This parameter change compensates for the reduced number of layers by creating stronger local insulation fields and improving overall electrical performance
3Object-generated harmful factors
If the distance between inner wiring layers is increased to reduce signal crosstalk, then the signal interference is reduced, but the board thickness increases
Solution Approach 1:
The patent introduces surface ground copper sheets as intermediary shielding layers between signal layers. These ground sheets act as mediators that block electromagnetic interference and reduce signal crosstalk without requiring increased distance between inner wiring layers, thus maintaining thin board profile
Data Source
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AI summary
A printed circuit board and a design method thereof are disclosed. The design method includes: wiring signal lines on an area basis at inner layers adjacent to outer surface layers; arranging the outer surface layers with no wiring or few wirings and interconnecting the outer surface layers through through vias, so that the outer surface layers function as a primary ground; and setting parameters of a line width and a layer height to control a target impedance value. The printed circuit board includes outer surface layers and two inner layers therebetween. The inner layers adjacent to the outer surface layers are used for arranging signal lines on an area basis; and the outer surface layers are arranged with no wiring or few wirings and are interconnected as a primary ground through through vias. The invention also discloses a mainboard of a terminal product using the printed circuit board.