Flip Chip Cleaning Using Centrifugal and Ultrasonic Removal
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Solution Overview
Problem
The complexity of cleaning flip chip assemblies due to the fragility of bumps and the narrow space between them, combined with the difficulty in removing charred flux residues and other contaminants, poses a challenge in achieving thorough and uniform cleaning.
Innovation Solution
An apparatus and method utilizing a chuck assembly with rotating flip chip carriers, centrifugal force to direct cleaning solutions, and ultrasonic/megasonic energy for effective removal of contaminants, including a pre-soaking and high-speed centrifugal force process to loosen and remove residues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-temperature reflow soldering process is used to join electronic components, then the soldering process is completed, but charred and caramelized flux residues are created that are difficult to remove
Solution Approach 1:
The patent applies preliminary action by pre-soaking the flip chip assembly in a cleaning solution before the main cleaning process. This pre-treatment loosens and softens the charred flux residues created during soldering, making them more susceptible to removal in subsequent cleaning steps. The pre-soaking step prepares the contaminated surfaces in advance, reducing the difficulty of residue removal.
Solution Approach 2:
The patent employs parameter changes by utilizing ultrasonic/megasonic energy to alter the physical state and properties of the cleaning solution and flux residues. The high-frequency vibrations change the energy parameters of the system, enhancing the cleaning solution's ability to penetrate and remove charred residues that are otherwise difficult to eliminate through conventional means.
2Productivity
If the bump dimension and pitch are reduced to achieve higher integration, then the assembly density increases, but the bump structure becomes more fragile and the gap between bumps and substrates becomes much smaller
Solution Approach 1:
The patent replaces aggressive mechanical cleaning methods with ultrasonic/megasonic energy-based cleaning. This substitution allows for effective contaminant removal without applying excessive mechanical stress that could damage the fragile, closely-spaced bump structures. The acoustic energy penetrates the narrow gaps and removes residues without requiring strong mechanical forces that would risk bump damage.
Solution Approach 2:
The patent utilizes mechanical vibration in the form of ultrasonic/megasonic frequencies to clean the flip chip assembly. The high-frequency vibrations create cavitation and acoustic streaming effects that effectively remove contaminants from narrow gaps and fragile structures without causing mechanical damage, enabling thorough cleaning of high-density assemblies with minimal risk to bump integrity.
3Productivity
If the gap between bumps and substrates is reduced to increase integration density, then the assembly becomes more compact, but the narrow space makes thorough and consistent cleaning a big challenge
Solution Approach 1:
The patent replaces conventional mechanical cleaning systems with ultrasonic/megasonic energy-based cleaning. This substitution enables effective penetration into narrow spaces and gaps between closely-spaced bumps, achieving thorough cleaning where mechanical methods would be inaccessible or ineffective. The acoustic energy propagates through the cleaning solution to reach contaminated surfaces in narrow gaps without requiring physical access that could damage the structure.
Solution Approach 2:
The patent employs mechanical vibration at ultrasonic/megasonic frequencies to overcome the accessibility challenges of narrow gaps. The high-frequency vibrations create cavitation bubbles and acoustic streaming that effectively reach and clean surfaces in tight spaces between bumps, achieving uniform cleaning throughout the assembly regardless of gap size or structural complexity.
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 enables thorough and uniform cleaning of flip chip assemblies by leveraging centrifugal force and ultrasonic/megasonic energy to overcome surface tension and diffusion barriers, ensuring effective removal of contaminants and enhancing mass transport rates.
Implementation Method 1
The flip chips held by flip chip carriers rotate as the chuck assembly spins, during rotation, DIW and/or a cleaning solution sprays onto the center region of the chuck will further spins into the flip chips at the chuck or loading plate peripheral by centrifugal force.
Implementation Method 2
at least one ultrasonic/megasonic device, the ultrasonic/megasonic device operates in the range from 5 KHz to 10 MHz, applying ultrasonic/megasonic energy during cleaning process can enhance the mass transport, reduce the diffusion double layer thickness by forming acoustic streaming layer near reacting surface and by local cavitation bubble implosion.
Implementation Method 3
applying ultrasonic/megasonic energy during cleaning process can enhance the mass transport, reduce the diffusion double layer thickness by forming acoustic streaming layer near reacting surface and by local cavitation bubble implosion.
Data Source
AI summary
An apparatus for cleaning flip chip assemblies is provided. The apparatus comprises: a chuck assembly; a motor coupled to the chuck assembly by a spindle; at least one carrier for holding flip chips; at least one spray nozzle for directing DIW, a cleaning solution, a gas or a vapor. Embodiments of the invention further provide methods for cleaning flip chip assemblies. The method comprises: loading at least one flip chip to the flip chip carriers; rotating the chuck assembly at a rotation speed; flowing DIW for rinsing the flip chips; flowing a cleaning solution for removing the contaminants; applying ultrasonic/megasonic energy to the flip chips; blowing a gas or a vapor via the spray nozzles for drying the flip chips; bringing the flip chips out of the flip chip carriers.