Sensor element and method for manufacturing sensor element
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Solution Overview
Problem
Current temperature measurement methods in power modules using NTC thermistors are limited by indirect thermal connections, leading to inaccurate and unreliable temperature readings due to insufficient adhesion and reliability of existing electrode materials and connection methods, particularly with gold, aluminum, and copper wires.
Innovation Solution
A sensor element design featuring a ceramic carrier with multilayer electrodes, including Cu, Ni, and Au layers for reliable soldering and aluminum wire bonding, and a metallized NTC thermistor for direct integration onto circuit boards, utilizing sputtering and conventional assembly techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If thick-film silver or gold pastes are applied using screen-printing process, then electrical connection is achieved, but adhesion strength and reliability are insufficient for bonding with gold, aluminum, or copper wires
Solution Approach 1:
The patent applies a composite electrode structure with multiple material layers (silver paste layer, copper layer, nickel layer, and gold layer) to achieve both reliable wire bonding and soldering connections. Each layer serves a specific function: silver paste provides adhesion to the NTC ceramic, copper provides electrical conductivity, nickel provides structural stability, and gold provides oxidation resistance and bonding surface quality.
Solution Approach 2:
The electrode is divided into distinct functional layers, with each layer performing a specific function. The silver paste layer contacts the NTC ceramic, the copper layer provides bulk conductivity, the nickel layer provides mechanical strength, and the gold layer provides the bonding surface. This segmentation allows optimization of each layer for its specific purpose.
2Measurement precision
If NTC thermistors are mounted on separate conductive paths on circuit board, then assembly is simplified, but temperature measurement accuracy is limited due to indirect thermal connection
Solution Approach 1:
The patent merges the sensor element directly with the circuit board by integrating the NTC thermistor onto the circuit board substrate with electrodes that directly contact conductor tracks. This eliminates separate mounting and creates a direct thermal and electrical connection between the sensor and the circuit board, improving temperature measurement accuracy while reducing overall device complexity.
3Manufacturing precision
If conventional screen-printing process with thick-film paste is used, then manufacturing is straightforward, but manufacturing precision and adhesion strength are insufficient
Solution Approach 1:
The patent uses screen-printing paste as an intermediary material that bridges the NTC ceramic and the metal layers. The silver paste contains adhesion promoters that bond to the ceramic surface, while also providing a conductive path to the underlying copper and nickel layers. This intermediary approach enables precise electrode patterns while maintaining strong adhesion and electrical conductivity.
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
Enables precise and reliable temperature monitoring by directly coupling the sensor to the circuit board, enhancing mechanical stability and reliability through matched thermal expansion coefficients and cost-effective manufacturing processes.
Implementation Method 1
utilizing sputtering and conventional assembly techniques
Data Source
Figure 1~4
Figure 5~6
AI summary
A sensor element (1) for measuring temperature is described, comprising a carrier (2), wherein the carrier (2) is made of an electrically insulating material and has a top surface (2a) and a bottom surface (2b), an NTC thermistor (3), wherein the NTC thermistor (3) is arranged on the top surface (2a) of the carrier (2), at least two first electrodes (4) for electrically contacting the sensor element (1), wherein the first electrodes (4) are arranged on the top surface (2a) of the carrier (2), and at least one second electrode (5), which is arranged on the bottom surface (2b) of the carrier (2), wherein the sensor element (1) is configured to be directly integrated in an electrically insulating manner. Furthermore, a method for manufacturing a sensor element (1) is described.