Current Sensing Resistor Electrode Segmentation for TCR Reduction
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Solution Overview
Problem
Current sensing techniques face challenges in minimizing the influence of Temperature Coefficient of Resistance (TCR) of electrode portions and welding spots on wire bonding, which deteriorate temperature characteristics and accuracy.
Innovation Solution
A current sensing resistor design featuring plate-shaped resistive elements with wider upper electrode portions and narrower lower electrode portions, along with a step portion, reduces electrode resistance and minimizes the contribution of electrode portions to the overall resistance value, thereby improving temperature characteristics and suppressing the influence of welding spots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If bonding wires are fixed to electrodes at positions as close to the resistive element as possible to minimize TCR influence, then temperature characteristics improve, but wire bonding becomes difficult due to unsuitable surface state from welding spots
Solution Approach 1:
The electrode is divided into three distinct portions: a first electrode portion that is substantially flush with the resistive element, a second electrode portion that is narrower and to be mounted on the wire pattern, and a step portion located between them. This segmentation allows different regions of the electrode to serve different functions: the first portion minimizes TCR influence by being close to the resistive element, while the second portion provides a suitable bonding surface for wire bonding, and the step portion separates these conflicting requirements.
2Measurement precision
If electrode width is increased at positions closer to the resistive element to reduce electrode resistance, then TCR influence is suppressed, but the structure becomes more complex
Solution Approach 1:
The electrode is designed with different widths at different locations: the first electrode portion has a greater width to reduce resistance and minimize TCR influence, while the second electrode portion has a narrower width suitable for mounting on the wire pattern. This local variation in geometry allows the electrode to optimize performance at critical locations without unnecessarily increasing overall device complexity.
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 suppresses the TCR influence of electrode portions and improves temperature characteristics, enhancing the accuracy and reliability of current sensing.
Implementation Method 1
Increasing the width of an area of each electrode at a position closer to the resistive element can reduce the resistance of the electrode at a position where wire bonding is to be performed. Thus, it is possible to reduce the contribution of the resistance value of each electrode portion to the resistance value of the entire shunt resistor and thus suppress the influence of TCR of the electrode portion
Data Source
AI summary
Provided is a current sensing resistor including a plate-shaped resistive element containing a resistive material, and plate-shaped electrodes joined to opposite sides of the plate-shaped resistive element, each plate-shaped electrode containing an electrode material. Each electrode includes an upper electrode portion that is substantially flush with the resistive element, a lower electrode portion to be mounted on a wire pattern, and a step portion located between the upper electrode portion and the lower electrode portion. The upper electrode portion is wider than the resistive element and the lower electrode portion in the direction orthogonal to the direction in which the electrodes are arranged.