Semiconductor Device Capacitor Pad Impedance Matching
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Solution Overview
Problem
In semiconductor devices, the insertion of a DC cut-off capacitor into signal wiring on a wiring board leads to significant deterioration of signal characteristics due to parasitic capacitance mismatch, resulting in increased transmission losses and reflection losses, especially at high frequencies.
Innovation Solution
The semiconductor device employs a configuration with a pair of capacitor pads and a capacitive component having parasitic inductance, where the characteristic impedance is matched by adjusting the parasitic capacitance and inductance to function as a band-pass filter, reducing parasitic effects and improving signal transmission performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the DC cut-off capacitor is inserted into the signal wiring on the wiring board, then the DC blocking function is achieved, but the signal transmission characteristics deteriorate due to parasitic capacitance mismatch
Solution Approach 1:
The patent converts the harmful parasitic inductance of the capacitor mounting structure into a beneficial element by designing it to function as a band-pass filter. The parasitic inductance, which originally caused signal deterioration, is now utilized to suppress unwanted frequency components while allowing the desired signal band to pass through, thereby improving overall signal transmission characteristics.
Solution Approach 2:
The patent changes the electrical parameters of the capacitor pad structure by carefully controlling the pad size, shape, and positioning to achieve a specific parasitic capacitance value. This parameter optimization ensures that the capacitor assembly forms an effective band-pass filter with the DC cut-off capacitor, resolving the impedance mismatch issue while maintaining DC blocking functionality.
2Loss of energy
If the capacitor pad size is reduced to minimize parasitic capacitance, then the characteristic impedance matching improves, but the mounting stability and electrical connection reliability deteriorate
Solution Approach 1:
The patent optimizes the capacitor pad parameters (size, shape, trace width) to achieve a specific parasitic capacitance range that enables band-pass filter functionality. This parameter optimization allows the use of larger pads for better mechanical stability while maintaining acceptable electrical performance through the filtering effect.
Solution Approach 2:
The patent accepts larger pad sizes for improved mounting stability and converts the resulting increased parasitic capacitance into a beneficial filtering effect. The larger pads provide better mechanical support and electrical connection reliability, while their parasitic capacitance, combined with parasitic inductance, creates a band-pass filter that improves signal characteristics.
3Reliability
If the parasitic capacitance of the capacitor pad is increased to improve mounting stability, then the mechanical reliability improves, but the signal transmission characteristics worsen due to impedance mismatch
Solution Approach 1:
The patent converts the harmful effect of increased parasitic capacitance (which would normally cause impedance mismatch and signal loss) into a beneficial filtering effect. By carefully controlling both parasitic capacitance and parasitic inductance, the design creates a band-pass filter where the previously harmful parameters now work together to suppress unwanted frequencies and pass the desired signal band.
Solution Approach 2:
The patent creates a composite electrical structure combining the DC cut-off capacitor, capacitor pads, and mounting structure into an integrated band-pass filter system. This composite structure utilizes the combined electrical characteristics (capacitance, inductance, and resistance) of all components to achieve superior signal transmission characteristics that cannot be obtained by optimizing individual components separately.
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 configuration effectively reduces transmission losses and reflection losses across a broader frequency range, including high frequencies, by actively utilizing parasitic inductance as a component of the band-pass filter, enhancing the overall signal transmission performance.
Implementation Method 1
a pair of a first capacitor pad and a second capacitor pad on which a capacitive component is mounted
Implementation Method 2
The semiconductor device employs a configuration with a pair of capacitor pads and a capacitive component having parasitic inductance
Data Source
AI summary
By changing the characteristic impedance of the transmission line depending on the location, the transmission line functions as a band-pass filter.