Chip-on-Board Pressure Sensor Buffer Layer
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Solution Overview
Problem
Pressure sensors face challenges in operating accurately and reliably under extreme thermal conditions due to stress induced by thermal expansion mismatches between the die and substrate, leading to output errors and mechanical damage.
Innovation Solution
A ceramic buffer layer with a thermal expansion coefficient intermediate between the pressure transducer and the chip-on-board substrate is used to reduce thermal stresses, and its high stiffness prevents flexural stresses from being transferred to the pressure transducer, allowing for improved adhesive selection and bonding methods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the pressure transducer is rigidly mounted directly onto the substrate, then the structural simplicity is improved, but the thermal expansion mismatch causes high package stress leading to output errors and mechanical damage
Solution Approach 1:
A buffer layer is introduced between the pressure transducer die and the substrate to act as a stress-absorbing intermediary. This buffer layer has a thermal expansion coefficient intermediate between that of the silicon die and the substrate, thereby reducing thermal mismatch stresses while also providing mechanical compliance to prevent stress transfer to the stress-sensitive die during assembly and operation.
2Strength
If high strength attach materials are used to bond the die to substrate, then the mechanical strength is improved, but the chemical resistance and stress transfer issues worsen under extreme thermal conditions
Solution Approach 1:
The buffer layer serves as a pre-positioned protective element that cushions the die from thermal and mechanical stresses before they can be transferred through the adhesive bond. By placing this compliant layer between the die and substrate, the system is pre-prepared to absorb expansion mismatches and reduce peak stresses on the die and adhesive interface during thermal cycling.
3Ease of manufacture
If the die is directly attached to the substrate, then the manufacturing process is simplified, but the thermal expansion coefficient mismatch introduces high package stress and non-repeatability
Solution Approach 1:
The buffer layer acts as a mediator that decouples the thermal expansion mismatch between the silicon die and the substrate. By selecting a buffer material with an intermediate thermal expansion coefficient, the system reduces differential expansion stresses while maintaining a relatively simple multi-layer assembly process that can be integrated into existing chip-on-board manufacturing workflows.
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 effectively reduces thermal and mechanical stresses, enhancing the reliability and accuracy of pressure sensors by mitigating creep and thermal errors, and preventing mechanical damage, thus improving the operational stability of pressure sensors in demanding environments.
Implementation Method 1
A buffer layer is generally located between the pressure transducer and the chip-on-board substrate to prevent or reduce thermally induced package stresses from being transferred to the pressure transducer
Implementation Method 2
A buffer layer is generally located between the pressure transducer and the chip-on-board substrate to prevent or reduce thermally induced package stresses from being transferred to the pressure transducer
Data Source
AI summary
A method of packaging for chip-on-board pressure sensor that includes a buffer layer with a coefficient of thermal expansion (CTE) intermediate between the transducer and a main chip-on-board substrate by which thermally induced package stresses can be greatly reduced or eliminated. Additionally, the use of a buffer layer with higher stiffness (elastic modulus) than the chip-on-board substrate further prevents or reduces flexural (bending) stresses from being transferred to the transducer. Such a buffer layer also enables a wider choice of materials for bonding and stable performance of pressure sensor in harsh media and environmental conditions. The pressure transducer can be adhesively bonded to a ceramic layer, which in turn can be adhesively bonded to an epoxy laminate chip-on-board substrate.