Spatial Light Modulation for Uniform Laser Reflow Heating
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Solution Overview
Problem
In semiconductor flip-chip mounting, laser reflow processes face issues with heat stress and productivity due to non-uniform laser beam intensity profiles, leading to potential bonding failures.
Innovation Solution
A laser beam irradiation apparatus with a spatial light modulator that rotates a phase pattern to uniformize the power density of the laser beam, ensuring consistent heating and preventing bonding failures by improving the intensity profile symmetry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If laser beam irradiation is used for reflow process, then productivity is improved and heat stress on substrate is reduced, but connection failure occurs due to non-uniform intensity profile
Solution Approach 1:
The patent applies local quality by modulating the laser beam intensity to create a non-uniform intensity distribution that compensates for the inherent non-uniformity of the laser source. The intensity is adjusted locally across different regions of the irradiated surface to achieve uniform heating, thereby preventing connection failure while maintaining the high productivity of laser reflow processing.
Solution Approach 2:
The patent changes the intensity parameter of the laser beam across different spatial locations to compensate for the non-uniform intensity profile. By adjusting the intensity distribution parameters, the system achieves uniform power density on the workpiece surface, eliminating connection failures caused by heating unevenness while preserving the productivity benefits of laser processing.
2Reliability
If mass reflow process is used to heat whole substrate, then bonding is achieved, but heat stress on substrate increases
Solution Approach 1:
The patent applies local quality by concentrating laser irradiation only on the regions requiring reflow (specific areas on the substrate and chips) rather than heating the entire substrate. This localized heating approach achieves the necessary bonding while minimizing heat stress on the overall substrate structure.
Solution Approach 2:
The patent replaces the conventional thermal conduction-based mass reflow system with a laser-based direct heating system. This substitution allows precise control of heat application, enabling bonding to occur with minimal heat stress on the substrate by delivering energy directly to the bump regions rather than heating the entire substrate uniformly.
3Reliability
If TCB process is used for bonding, then connection is achieved, but productivity decreases due to long cooling time
Solution Approach 1:
The patent replaces the TCB process with laser beam irradiation for achieving the reflow connection. This substitution eliminates the need for mechanical pressurization and extended cooling periods, as the laser process achieves bonding through direct localized heating that cools rapidly after irradiation, thereby significantly improving productivity while maintaining reliable connections.
4Manufacturing precision
If phase pattern is rotated to uniformize power density, then heating uniformity is improved, but device complexity increases
Solution Approach 1:
The patent applies dynamics by making the phase pattern rotatable rather than fixed. The spatial light modulator can dynamically adjust and rotate the phase pattern to optimize the intensity distribution, achieving uniform heating across the irradiated area. This dynamic adjustment capability improves manufacturing precision without requiring complex mechanical moving parts, as the complexity is managed through programmable optical phase modulation.
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 apparatus effectively suppresses connection failures by achieving uniform heating across semiconductor chips, enhancing productivity through efficient reflow of bumps and improved bonding processes.
Implementation Method 1
a spatial light modulator that modulates the laser beam emitted from the laser beam source, according to a phase pattern
Implementation Method 2
The controller uniformizes the power density of the laser beam with which the plate-shaped workpiece is irradiated, by rotating the phase pattern
Implementation Method 3
a laser beam source that emits the laser beam and a spatial light modulator that modulates the laser beam
Implementation Method 4
reflow of the bumps included in an irradiated range of the laser beam is caused by irradiating a region corresponding to the semiconductor chip mounted over the substrate with the laser beam
Data Source
AI summary
A laser beam irradiation unit of a laser beam irradiation apparatus includes a laser beam source that emits a laser beam and a spatial light modulator that modulates the laser beam emitted from the laser beam source, according to a phase pattern, and that emits the laser beam. A controller has a storing section that stores the phase pattern to be displayed in the spatial light modulator and a rotation instructing section that rotates the phase pattern stored in the storing section. The controller uniformizes the power density of the laser beam with which a plate-shaped workpiece is irradiated, by rotating the phase pattern while the plate-shaped workpiece is irradiated with the laser beam.