Semiconductor Wiring Board Impedance Control via Insulating Layer Thickness
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Solution Overview
Problem
Impedance mismatch between semiconductor elements and signal wires on a wiring board leads to signal reflection and waveform disturbances, necessitating effective impedance matching and noise reduction for stable semiconductor device operation.
Innovation Solution
A semiconductor device configuration featuring a wiring board with varying thicknesses of insulating layers over power, signal, and ground wires, and a metal film connected to the ground potential, which forms a decoupling capacitor to stabilize power supply and reduce noise, while optimizing the characteristic impedance of signal wires through controlled thickness of solder resist.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a uniform thickness insulating layer is used over all wires, then the manufacturing process is simple, but the characteristic impedance of signal wires cannot be controlled and power supply stability is poor
Solution Approach 1:
The insulating layer is designed with different thicknesses in different regions: a first thickness over the signal wire for impedance control, and a second thickness over the power wire for capacitance control. This local differentiation allows each wire type to have optimized electrical characteristics without requiring complete structural redesign.
Solution Approach 2:
The insulating layer is segmented into multiple regions with different thicknesses corresponding to different wire functions. The layer is divided into a first region covering the signal wire and a second region covering the power wire, enabling independent optimization of each region's electrical properties.
2Reliability
If decoupling capacitors are added to stabilize power supply, then power supply stability improves, but the number of components and device complexity increases
Solution Approach 1:
The insulating layer itself is designed to function as a decoupling capacitor by creating a capacitance between the power wire and ground wire through its dielectric material. This merges the insulating function with the decoupling capacitor function, eliminating the need for separate capacitor components while maintaining power supply stability.
Solution Approach 2:
The insulating layer performs multiple functions simultaneously: it provides electrical insulation between conductors, controls characteristic impedance of signal wires through its thickness, and acts as a decoupling capacitor for power supply stabilization. This multi-functionality reduces the total component count while achieving multiple objectives.
3Reliability
If impedance matching is not conducted, then the wiring board design is simple, but signal reflections occur and waveform distortion leads to malfunction
Solution Approach 1:
The characteristic impedance of the signal wire is controlled by adjusting the thickness of the insulating layer in the first region. By changing this physical parameter, the impedance can be matched to standard values (e.g., 50 ohms), preventing signal reflections and waveform distortion without adding complex impedance matching circuits.
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
The solution ensures impedance matching, reduces signal reflections, stabilizes power supply, and enhances noise reduction, thereby improving the reliability and performance of semiconductor devices by controlling the characteristic impedance of signal wires and capacitance of power planes.
Implementation Method 1
the metal film and the power wire and the insulating layer interposed between the metal film and the power wire form a decoupling capacitor
Implementation Method 2
a thickness of the insulating layer covering the power wire is different from a thickness of the insulating layer covering the signal wire
Data Source
AI summary
A semiconductor device includes: a board; a power wire formed on the board; a signal wire formed on the board; a ground wire formed on the board; an insulating layer covering the signal wire, the power wire and the ground wire; and a metal film formed on the insulating layer, wherein a thickness of the insulating layer covering the power wire is different from a thickness of the insulating layer covering the signal wire, and the metal film is connected to a ground potential.