Acoustic Resonator Die Bonding on PCB Without Flux Contamination
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Solution Overview
Problem
Existing methods for fabricating acoustic wave resonator devices using flip chip mounting with flux and soldering result in contamination issues and require a washing step, which can disrupt the die-to-PCB bond and fail to completely remove contamination from the active die surface.
Innovation Solution
The method involves thermosonic bonding of bulk acoustic wave sensor dies to printed circuit boards without using flux or solder, using gold electrical connection bumps and pads, and applying ultrasonic energy to form bonds, which eliminates the need for washing and provides a strong, contamination-free connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flip chip mounting with flux and soldering is used, then electrical connection between die and PCB is achieved, but contamination occurs on the active die surface and washing steps are required
Solution Approach 1:
The invention extracts and eliminates the flux and soldering steps from the bonding process. By using direct thermosonic bonding of gold bumps to gold pads, the harmful flux residue that causes contamination is completely removed from the process, achieving reliable electrical connection without contamination on the active die surface.
Solution Approach 2:
The invention replaces the chemical bonding mechanism (flux and solder) with a mechanical/physical bonding mechanism (thermosonic bonding of gold bumps). This substitution eliminates the need for chemical flux that causes contamination, while still achieving strong electrical and mechanical connection between die and PCB.
2Object-generated harmful factors
If washing step is performed after flux and soldering, then contamination is reduced, but die-to-PCB bond may be disrupted and fail
Solution Approach 1:
The invention converts the potential harm of skipping wash steps into a benefit by designing a bonding process that generates no contamination in the first place. The thermosonic bonding method creates clean bonds without flux residue, so no washing is needed and bond reliability is maintained.
3Reliability
If wash fixture is used during washing, then bond disruption is minimized, but process complexity increases
Solution Approach 1:
The invention extracts and eliminates the entire washing process and wash fixture from the fabrication sequence. By using thermosonic bonding without flux, the need for washing is completely removed, simplifying the process while maintaining bond reliability.
4Reliability
If flux and solder are used for bonding, then strong electrical connection is achieved, but contamination remains on active die surface
Solution Approach 1:
The invention changes the bonding parameters by using thermosonic bonding conditions (temperature, pressure, ultrasonic vibration) that enable direct metal-to-metal bonding of gold bumps to gold pads. This parameter change eliminates the need for flux and solder, achieving strong electrical connection with a clean active die surface.
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 approach enables effective and contamination-free electrical connection of bulk acoustic wave sensor dies to printed circuit boards, enhancing the reliability and cleanliness of the bonding process, suitable for biosensing applications.
Implementation Method 1
applying ultrasonic energy to the die to bond the first and the second electrical connection bumps of the die with the first and the second connection pads of the PCB respectively
Implementation Method 2
heating the die, the PCB, or both
Implementation Method 3
a bulk acoustic wave sensor that comprises a piezoelectric structure electrically connected to a first and a second electrode
Data Source
AI summary
Assemblies including a bulk acoustic wave acoustic sensor die having a first and an opposing second major surface, the die including a piezoelectric structure, a first and a second electrode electrically connected to the piezoelectric structure, and an active surface on the first major surface of the die; a printed circuit board (PCB), the PCB having a first major surface and an opposing second major surface and including a slot spanning from the first major surface to the second major surface through the PCB; a first bond electrically and mechanically connecting the die to the PCB; and a second bond electrically and mechanically connecting the die to the PCB, wherein the first and the second bonds are located on either side of the slot through the PCB and the active surface of the die is above the slot in the PCB.