Acousto-Optic Beam Deflection for Constant-Dosage Laser Ablation
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Solution Overview
Problem
Current laser processing technologies face challenges in achieving high-speed, precise, and efficient ablation of fine features in chip packaging, particularly in maintaining constant beam power and velocity, controlling trace width, and achieving accurate intersections with minimal depth variation, due to limitations in beam positioning and interaction with the ablation plume.
Innovation Solution
The use of an acousto-optic deflector (AOD) subsystem in combination with galvo positioning systems, which includes two AODs to deflect a continuous wave laser beam along multiple axes, allowing for high-speed beam positioning and conditioning, enabling dithering to change beam dimensions and intensity profiles, and correcting for galvo errors to maintain constant dosage and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If traditional galvo beam positioners are used for high-speed laser processing, then beam positioning capability is provided, but the system cannot achieve high enough velocities (1-10 m/s) due to dynamic limits of the beam positioner
Solution Approach 1:
The beam positioner is segmented into two independent subsystems: a galvo subsystem for coarse positioning and an AOD subsystem for fine positioning. The galvo mirrors provide large-angle deflection for overall beam direction, while the AODs provide rapid micro-adjustments for precise spot placement. This segmentation allows each subsystem to operate within its optimal performance range, enabling both high speed and high accuracy.
Solution Approach 2:
The AOD subsystem acts as an intermediary between the galvo subsystem and the workpiece. It receives the beam from the galvo positioner and performs final high-precision positioning and pulse generation. The AODs serve as a buffer that absorbs the dynamic limitations of the galvo system while providing the necessary positioning precision at high velocities.
2Productivity
If beam velocity is increased to improve throughput, then processing speed increases, but maintaining constant dosage becomes difficult due to velocity variations
Solution Approach 1:
The system implements feedback control by continuously monitoring beam velocity and adjusting the AOD deflection parameters accordingly. The control system calculates the instantaneous velocity based on the programmed trajectory and real-time position feedback, then modifies the AOD drive signals to maintain constant dosage despite velocity variations. This closed-loop control ensures consistent ablation depth and quality throughout the processing path.
Solution Approach 2:
The system dynamically changes the AOD deflection angle and pulse repetition frequency as parameters to compensate for velocity variations. When velocity increases, the system adjusts the AOD parameters to maintain the appropriate dosage rate. This real-time parameter adjustment allows the system to process at high speeds while maintaining manufacturing precision.
3Productivity
If high peak power laser pulses are used to ablate material efficiently, then ablation rate increases, but thermal side effects such as melting and cracking occur
Solution Approach 1:
The system uses periodic ultrafast laser pulses with durations in the picosecond to nanosecond range. These extremely short pulses deliver high peak power to ablate material efficiently while the brief duration prevents heat diffusion to surrounding areas, avoiding melting and cracking. The pulse repetition rate is optimized to provide continuous material removal without thermal accumulation.
Solution Approach 2:
The ultrafast laser pulses induce direct phase transitions from solid to plasma or gas phase through multiphoton absorption and avalanche ionization, bypassing the liquid phase that causes melting. This non-thermal ablation mechanism allows high removal rates without the harmful thermal side effects associated with conventional continuous wave or long-pulse lasers.
4Adaptability or versatility
If feature characteristics are changed to process arbitrary shapes and sizes, then versatility improves, but time delays increase when changing laser processing spot characteristics
Solution Approach 1:
The AOD subsystem provides dynamic control of beam characteristics including spot size, shape, and position. By electronically adjusting the AOD drive signals, the system can rapidly reconfigure the laser spot to match any desired feature geometry without mechanical repositioning or optical realignment. This dynamic control enables processing of arbitrary shapes and sizes with minimal reconfiguration time.
Solution Approach 2:
The system changes laser processing parameters (spot diameter, intensity profile, pulse duration) by adjusting AOD operating parameters in real-time. Different feature geometries are achieved by modifying the acoustic field in the AOD, which directly controls the diffracted beam characteristics. This parameter-based control allows instantaneous adaptation to different feature requirements without time-consuming mechanical adjustments.
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 flexible, high-speed, and precise laser processing with reduced thermal side effects, improved throughput, and accurate control of feature dimensions and intersections, overcoming the limitations of traditional systems by maintaining constant beam power and velocity, and minimizing depth variation.
Implementation Method 1
an acousto-optic deflector (AOD) subsystem operative to deflect a continuous wave laser beam
Data Source
AI summary
A method includes receiving, during a period of time, a continuous wave laser beam at an acousto-optic deflector (AOD) having a first AOD and a second AOD. A plurality of laser pulses is generated from the received beam using the first acousto-optic deflector (AOD) to the laser beam along a first axis and using the second AOD to deflect the laser beam deflected by the first AOD along a second axis.