Sensor Module Conductive Bonding Members Varying Melting Points
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Solution Overview
Problem
In sensor modules, the use of low-melting-temperature solders like Sn—Bi eutectic solder for bonding inertial sensors to substrates results in low mechanical strength and thermal fatigue resistance, leading to instability and reliability issues due to thermal expansion coefficient differences between the sensor and the substrate.
Innovation Solution
A sensor module design employing a first conductive bonding member with a higher melting point and Young's modulus for bonding the lead to the substrate, and a second conductive bonding member with a lower melting point and higher Young's modulus for bonding the inertial sensor to the substrate, using lead-free solders like Sn-3.0Ag-0.8Cu-3.0Bi-0.02Ni, which coexist in a solid and liquid phase, to enhance bonding stability and prevent remelting.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solder having a low melting temperature (e.g., Sn-Bi eutectic solder) is used for bonding the inertial sensor to the substrate, then the subsequent soldering operation does not affect the previous soldering, but the solder has low mechanical strength and thermal fatigue resistance, leading to reliability issues
Solution Approach 1:
The patent divides the bonding structure into two distinct conductive bonding members: a first conductive bonding member (solder) for bonding the lead to the substrate, and a second conductive bonding member (adhesive) for bonding the inertial sensor to the substrate. This segmentation allows each bonding member to have optimized properties for its specific function, resolving the contradiction between low melting temperature and mechanical strength requirements.
Solution Approach 2:
The patent applies different material properties to different locations in the bonding structure. The first conductive bonding member uses solder with appropriate melting temperature for electrical connection, while the second conductive bonding member uses adhesive with high mechanical strength and thermal fatigue resistance for sensor mounting. This local differentiation of material properties resolves the contradiction.
2Stability of the object's composition
If a solder having a low melting temperature is used for bonding, then remelting during subsequent operations is prevented, but the solder deteriorates under repeated thermal stress from thermal expansion coefficient differences
Solution Approach 1:
The patent segments the bonding function into two parts: the first conductive bonding member handles electrical connection with controlled melting behavior, while the second conductive bonding member handles mechanical support and sensor attachment with high stability. This segmentation prevents the deterioration issue by assigning thermal stress resistance to the adhesive material.
Solution Approach 2:
The patent employs composite material strategy by using different materials for different bonding functions. The first conductive bonding member uses solder material optimized for electrical properties, while the second conductive bonding member uses adhesive material optimized for mechanical properties and thermal stability. This composite approach resolves the contradiction between composition stability and reliability.
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 enhances the reliability and stability of the sensor module by preventing deterioration and remelting, ensuring long-term electrical coupling and improved detection accuracy by setting the second Young's modulus higher than the first, thus addressing the mechanical and thermal challenges faced with traditional solders.
Implementation Method 1
a first conductive bonding member having a first melting point and a first Young's modulus, and bonding the lead and the first terminal
Implementation Method 2
a second conductive bonding member having a second melting point lower than the first melting point and a second Young's modulus higher than the first Young's modulus, and bonding the inertial sensor and the second terminal
Data Source
AI summary
A sensor module includes: a substrate including a first terminal and a second terminal; a first conductive bonding member having a first melting point and a first Young's modulus; a lead bonded to the first terminal by the first conductive bonding member; a second conductive bonding member having a second melting point lower than the first melting point and a second Young's modulus higher than the first Young's modulus; and an inertial sensor bonded to the second terminal by the second conductive bonding member.