PCB Pad Capacitance Reduction via Dielectric Passage
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Solution Overview
Problem
Existing printed circuit boards (PCBs) and memory modules face challenges in reducing pad capacitance while maintaining desired impedance, as small passive elements can detach easily and result in signal deterioration, limiting the size of pads and increasing capacitance.
Innovation Solution
The PCB design incorporates a dielectric passage and conductive lines in the first reference layer to form a return path for signals, reducing pad capacitance by increasing the thickness of the dielectric layer and using a conductive line to prevent signal delay, thereby enhancing impedance without increasing the board thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the pad size is reduced to decrease capacitance, then the capacitance is reduced, but the impedance cannot be maintained and signal integrity deteriorates
Solution Approach 1:
The patent introduces a dielectric passage extending in the thickness direction (vertical dimension) beneath the pad, rather than only modifying the pad's horizontal dimensions. This vertical dimension allows capacitance reduction through increased effective dielectric thickness while maintaining pad area for impedance control, thus resolving the contradiction between reducing capacitance and maintaining signal integrity.
Solution Approach 2:
The patent changes the dielectric parameter by introducing a dielectric passage filled with dielectric material, effectively increasing the dielectric thickness between the pad and reference layer. This parameter change allows capacitance reduction without reducing pad size, thereby maintaining both low capacitance and high signal integrity.
2Length of moving object
If a small passive element is used to reduce discontinuous section, then the discontinuous section is reduced, but the passive element may detach due to external impact
Solution Approach 1:
The patent extracts the passive element (resistor) from the traditional surface-mounted configuration and integrates it directly into the PCB structure by forming a resistance pad that is part of the circuit trace. This eliminates the separate passive element that could detach, while maintaining the desired electrical discontinuity section.
Solution Approach 2:
The patent merges the passive element function directly into the PCB trace structure by forming a resistance pad that is integrated with the circuit trace. This combination eliminates the separate mounting interface that could fail under external impact, while maintaining the electrical discontinuity section.
3Reliability
If the pad size is increased to maintain impedance, then the impedance is maintained, but the capacitance increases and signal characteristics deteriorate
Solution Approach 1:
The patent resolves this contradiction by utilizing the vertical dimension through the dielectric passage. The pad area can be maintained for impedance control while the dielectric passage increases the effective separation distance in the thickness direction, reducing capacitance without compromising either parameter.
Solution Approach 2:
The patent segments the dielectric space by introducing a dielectric passage that divides the space between the pad and reference layer. This segmentation allows the pad to maintain its area for impedance control while the passage creates an air gap or reduced dielectric constant region that lowers capacitance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design effectively reduces pad capacitance, improving signal integrity and impedance, while preventing signal delay and maintaining a compact PCB size.
Implementation Method 1
A capacitance of the pad may correspond to a distance between the pad and the second reference layer
Implementation Method 2
a dielectric passage for forming a return path of a signal
Implementation Method 3
a conductive line disposed in the dielectric passage and disposed to form a transmission path of the signal
Data Source
AI summary
A printed circuit board (PCB) includes a first insulating layer, a pad disposed on the first insulating layer, and a first reference layer on which the first insulating layer is disposed, the first reference layer including a dielectric passage for forming a return path of a signal that is transmitted to the pad, and a conductive line disposed in the dielectric passage and disposed to form a transmission path of the signal. The PCB further includes a second insulating layer on which the first reference layer is disposed, and a second reference layer on which the second insulating layer is disposed, the second reference layer further forming the return path. A capacitance of the pad corresponds to a distance between the pad and the second reference layer.