Load Sensor Elastic Bonding for Thermo-Mechanical Stress
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Solution Overview
Problem
Current load sensors face measurement errors and instability due to thermo-mechanical stresses from packaging and assembly processes, which are exacerbated by differences in thermal expansion coefficients between packaging materials and silicon-based sensor structures, leading to variable and unsatisfactory precision in force and pressure measurements.
Innovation Solution
A load-sensing device that uses elastic or viscoelastic elements to maintain the sensor unit in contact with a deformable substrate within the package, allowing the substrate to deform and measure loads indirectly, thereby minimizing thermo-mechanical stresses and enhancing stability through elastic bonding, which prevents foreign material-induced stresses and allows for precise force detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional packaging materials with different thermal expansion coefficients are used, then the package provides mechanical protection and structural strength, but thermo-mechanical stresses cause measurement errors and drifts
Solution Approach 1:
The patent introduces an intermediary layer between the sensor die and the package substrate. This intermediary layer acts as a stress buffer that decouples the thermal expansion differences between the silicon sensor die and the packaging materials, thereby preventing thermo-mechanical stresses from reaching the sensor while maintaining mechanical protection
Solution Approach 2:
The patent modifies the thermal and mechanical parameters of the packaging structure by selecting materials and designing structures with matched thermal expansion coefficients. This parameter matching approach ensures that the package expands and contracts harmoniously with the sensor die during temperature variations, eliminating differential stress
2Stability of the object's composition
If the sensor die is rigidly bonded to the package substrate, then assembly is simplified and structural stability is improved, but thermal expansion differences cause die warpage and measurement drift
Solution Approach 1:
The patent transitions from a rigid, fixed bonding approach to a dynamic, compliant bonding approach. The bonding structure is designed to accommodate thermal expansion and contraction movements, allowing the sensor die to maintain proper alignment and contact with the substrate throughout temperature cycles without generating stress concentration points
Solution Approach 2:
The patent divides the bonding interface into multiple segments or zones with different compliance characteristics. This segmentation allows different parts of the package to handle thermal stress differently, with some areas providing rigid support and others providing compliant stress relief, thereby maintaining both structural stability and measurement reliability
3Ease of manufacture
If simple moulding packaging techniques are used, then manufacturing cost and complexity are reduced, but high stresses during resin injection and cooling cause measurement errors
Solution Approach 1:
The patent incorporates stress-compensating structural features into the package design before the moulding process begins. These pre-designed stress relief features, such as compliant mounting structures or stress-absorbing geometries, are built into the package to cushion against the high stresses that will occur during resin injection and cooling, preventing measurement errors without requiring complex manufacturing processes
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 provides high stability in output signals across varying temperatures, with simulations showing significant reduction in measurement drift and improved precision, enabling accurate detection of forces and pressures without the limitations of traditional packaging-induced stresses.
Implementation Method 1
A load-sensing device is provided, as defined in the attached claims. In practice, the present device detects a load (where by this term is meant a force, a pressure, or a torque), indirectly by detecting the deformation of a deformable substrate on which the load acts. A sensor unit is kept in contact with the deformable substrate through elastic or viscoelastic elements
Implementation Method 2
The measurement may be of a piezoresistive type, and to this end piezoresistors are integrated in or on the membrane
Data Source
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AI summary
A load-sensing device (10), arranged in a package (12) forming a chamber (24). The package (12) has a deformable substrate (21) configured, in use, to be deformed by an external force. A sensor unit (11) is in direct contact with the deformable substrate (21) and is configured to detect deformations of the deformable substrate. An elastic element (15) is arranged within of the chamber (24) and acts between the package (12) and the sensor unit (11) to generate, on the sensor unit, a force keeping the sensor unit in contact with the deformable substrate. For example, the deformable substrate is a base (21) of the package (12), and the elastic element is a metal lamina (15) arranged between the lid (22) of the package (12) and the sensor unit (11). The sensor unit (11) may be a semiconductor die integrating piezoresistors.