Laser Reflow Beam Shaping for Inclined Chip Bonding
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Solution Overview
Problem
The laser reflow process for semiconductor chip bonding faces connection failures due to uneven heating when chips are placed inclined on the board, leading to areas of incomplete bonding, which reduces productivity and yield.
Innovation Solution
A method using a laser reflow apparatus with a spatial light modulator to adjust the laser beam's irradiation range according to the detected inclination of each chip, ensuring uniform heating and bonding by rotating the phase pattern of the laser beam to match the chip's orientation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a holding table with a rotational axis is used to rotate the table according to the inclination of chips, then alignment of irradiation positions is improved, but it takes time to control the rotational axis, which lowers productivity
Solution Approach 1:
The patent replaces the mechanical rotational holding table system with an optical phase pattern rotation system. The spatial light modulator rotates the laser beam's phase pattern electronically to match chip inclination, eliminating the need for mechanical rotation of the holding table. This substitution of mechanical system with optical/electronic system resolves the contradiction by maintaining alignment precision while eliminating the time-consuming mechanical rotation control.
Solution Approach 2:
The patent makes the laser beam irradiation system dynamically adaptable by rotating the phase pattern according to the detected inclination of each chip. Instead of mechanically adjusting the holding table for each chip, the system dynamically rotates the optical phase pattern to match the chip orientation, enabling rapid adaptation without mechanical movement and thus maintaining both precision and productivity.
2Productivity
If the laser beam is applied to a predetermined area without considering chip inclination, then the process is simple and fast, but only part of each chip is heated, causing connection failures
Solution Approach 1:
The patent applies local quality by making the laser beam's phase pattern rotatable to match each chip's specific inclination. Instead of using a fixed predetermined irradiation area, the system locally adapts the beam shape and orientation to each chip's position and angle. This ensures that the entire surface of each inclined chip receives uniform heating, maintaining bonding reliability while keeping the process efficient through automated phase pattern rotation.
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 ensures consistent bonding across the entire chip surface, reducing thermal stress and connection failures, thereby improving yield and productivity by ensuring proper alignment and bonding of semiconductor chips to the board.
Implementation Method 1
a laser beam source, an image focusing assembly for focusing an image of a laser beam emitted from the laser beam source
Implementation Method 2
irradiating each semiconductor chip with the laser beam from another surface side opposite to the one surface to reflow the bumps
Implementation Method 3
a spatial light modulator that is disposed between the laser beam source and the image focusing assembly and that modulates the laser beam emitted from the laser beam source, according to a phase pattern
Data Source
AI summary
A laser reflow method includes preparing a workpiece including a board and semiconductor chips each having one or more bumps formed on one surface thereof, the semiconductor chips being placed on the board with the bumps interposed therebetween. An inclination detection step captures an image of one semiconductor chip and detects an inclination of the semiconductor chip within the captured image. A laser beam irradiation step irradiates each semiconductor chip with a laser beam from another surface side opposite to the one surface to reflow the bumps formed within an irradiated range of the workpiece. A phase pattern displayed by a spatial light modulator is rotated in such a manner as to agree with the inclination of the detected semiconductor chip, to thereby rotate an irradiation range of the laser beam within an irradiated surface of the workpiece, before the semiconductor chips are irradiated with the laser beam.