SAW Device Dummy Chip Thermal Stress Reduction
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Solution Overview
Problem
Existing acoustic wave devices face challenges in thermal expansion mismatch and stress application due to resin thermal expansion, which can affect the propagation characteristics and stability of surface acoustic waves.
Innovation Solution
Incorporating a dummy chip with a lower thermal expansion coefficient and a thicker substrate, bonded to a piezoelectric substrate with a support substrate, and an IDT electrode configuration, which helps in temperature compensation and reduces stress on the SAW chip, while maintaining a flat resin top surface for improved structural and thermal stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a resin part covers the acoustic wave chip for sealing, then the device achieves protection and sealing, but thermal expansion mismatch between the resin and piezoelectric substrate causes stress and affects SAW propagation characteristics
Solution Approach 1:
A dummy chip is introduced as an intermediary component between the resin part and the acoustic wave chip. The dummy chip includes a dummy substrate with thermal expansion characteristics that match the resin part, serving as a buffer that absorbs thermal expansion stress. This mediator prevents direct stress transmission from the resin to the piezoelectric substrate, thereby protecting the SAW propagation characteristics while maintaining effective sealing protection.
Solution Approach 2:
The dummy substrate is designed with specific thermal expansion parameters that match or are compatible with the resin part, rather than using a substrate with mismatched thermal properties. By changing the thermal expansion parameter of the dummy substrate to align with the resin, the system accommodates thermal expansion during temperature changes, preventing stress concentration on the acoustic wave chip and maintaining reliable operation under thermal conditions.
2Volume of moving object
If the piezoelectric substrate is made thinner to reduce device size, then miniaturization is achieved, but the substrate becomes more susceptible to stress and deformation
Solution Approach 1:
The dummy chip acts as a structural support intermediary that compensates for the reduced strength of the thin piezoelectric substrate. By positioning the dummy substrate adjacent to and supporting the piezoelectric substrate, the system gains additional mechanical strength without increasing the overall device volume significantly. The dummy substrate serves as a reinforcement element that prevents deformation while maintaining the miniaturized form factor.
3Productivity
If two acoustic wave chips are mounted on one mounting substrate for higher integration, then productivity increases, but stress distribution becomes uneven and affects device stability
Solution Approach 1:
When multiple acoustic wave chips are mounted on a single mounting substrate, dummy chips are strategically positioned between and around the functional chips. These dummy chips serve as stress distribution mediators that equalize the mechanical load and thermal expansion forces across the mounting substrate. By distributing stress through the dummy chips, the system maintains uniform stress patterns that prevent localized deformation and ensure stable operation of all integrated chips.
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 stress, stabilizes the SAW chip's electrical characteristics, and improves the structural integrity and thermal management of the acoustic wave device, enhancing its performance and reliability.
Implementation Method 1
The support substrate is lower in thermal expansion coefficient than the first piezoelectric substrate and is thicker than the first piezoelectric substrate
Implementation Method 2
a first IDT (interdigital transducer) electrode which is located on a surface of the first piezoelectric substrate on an opposite side to the support substrate
Data Source
AI summary
A SAW device includes a mounting substrate including a mounting surface, a SAW chip mounted on the mounting surface, a dummy chip mounted on the mounting surface, and a resin part covering the acoustic wave chip and the dummy chip. The dummy chip includes an insulating dummy substrate, and one or more dummy terminals which are located on a surface of the dummy substrate on the mounting surface side and are bonded to the mounting surface. The dummy chip configures an open end when electrically viewed from the mounting substrate side.