Acoustic Wave Device Protective Cover for Molding Compound Intrusion
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Solution Overview
Problem
Acoustic wave devices in communication systems are sensitive to mass loading, which can alter their frequency response due to molding compound intrusion during packaging, and existing bonding technologies like ultrasonic flip chip bonding are costly and have low fabrication rates, while copper pillar reflow flip chip bonding allows easier compound intrusion due to larger spacing.
Innovation Solution
A protective structure with a metal covering layer having a concave surface and bottom rim is formed over the resonant area of the acoustic wave device, creating a cavity to prevent molding compound intrusion, using electroplating and a sacrificial layer removal process, and can be applied in flip chip or wire bonding technologies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If copper pillar reflow flip chip bonding technology is used to reduce fabrication cost and improve fabrication rate, then fabrication cost is reduced and fabrication rate is improved, but the space between chip and packaging substrate increases to more than 20 μm which allows molding compound to flow onto the device surface more easily
Solution Approach 1:
A protective cover structure is introduced as an intermediary element between the acoustic wave device and the molding compound. This cover includes a bottom rim connected to the device and a concave surface forming a cavity, physically blocking the molding compound from contacting the resonant area while allowing the device to be bonded using copper pillar reflow technology with larger spacing.
2Object-affected harmful factors
If ultrasonic flip chip bonding technology is used to bond surface acoustic wave filters, then molding compound intrusion is avoided with 10 μm spacing, but fabrication cost increases due to gold bump requirement and fabrication rate decreases
Solution Approach 1:
The protective cover serves as a mediator that enables the use of copper pillar reflow bonding (faster, cheaper process) while maintaining the protection benefit of smaller spacing processes. The cover physically prevents molding compound intrusion regardless of the bonding method used.
Solution Approach 2:
The invention changes the spatial parameter by creating a controlled cavity structure with specific dimensions (bottom rim connection and concave surface). This structural parameter change allows larger bonding spacing (20+ μm) to effectively function as if smaller spacing existed, preventing compound intrusion while enabling faster bonding processes.
3Strength
If any material is coated on the surface of the acoustic wave device during fabrication and packaging, then the device surface is protected, but mass loading effect changes the boundary condition and alters frequency response characteristic
Solution Approach 1:
The protective function is segmented into two separate components: the protective cover structure that prevents molding compound intrusion, and the device surface that remains free of mass-loading materials. This segmentation allows protection without direct surface coating on the resonant area.
Solution Approach 2:
Instead of protecting the device surface in the horizontal plane by coating materials, the invention moves to a vertical dimension by creating a three-dimensional protective cover with a bottom rim and concave surface. This dimensional transition provides protection while keeping the resonant surface free of mass-loading materials.
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 protective structure effectively prevents molding compound from affecting the frequency response of acoustic wave devices, simplifies the fabrication process, and improves packaging yield by providing a stable, non-collapsible cover that can be used in various bonding technologies.
Implementation Method 1
covering a metal covering layer on the sacrificial layer by electroplating method
Data Source
AI summary
A protective cover for an acoustic wave device and a fabrication method thereof, for protecting an acoustic wave device having a resonant area during a packaging operation so as to avoid molding compound flowing onto the resonant area of the acoustic wave device. The fabrication method comprises: defining a sacrificial area on the acoustic wave device; forming a sacrificial layer on the sacrificial area; covering a metal covering layer on the sacrificial layer and connecting a bottom rim of the metal covering layer to the acoustic wave device and forming an opening between the bottom rim of the metal covering layer and the acoustic wave device; and removing the sacrificial layer to form a cavity between the metal covering layer and the resonant area by using a chemical solution, wherein the chemical solution enters from the opening between the metal covering layer and the acoustic wave device.