CO Laser Via-Hole Drilling with Pulse Clipping
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Solution Overview
Problem
Current CO2 lasers used for drilling via-holes in printed circuit boards face limitations in achieving smaller hole sizes and closer spacing due to their long wavelength, and potential mid-IR lasers are costly and suffer from collateral thermal damage issues when operated in pulsed mode.
Innovation Solution
A sealed-off CO laser system is modified to operate in a pulsed manner with an acousto-optic modulator for pulse clipping and a dispersion-compensator to correct beam dispersion, combined with achromatic focusing optics for precise focusing on the PCB, allowing for efficient and effective via-drilling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If CO2 lasers are used for via-drilling, then drilling speed and power output are improved, but minimum hole size and spacing are limited due to long wavelength
Solution Approach 1:
The patent changes the fundamental parameter of laser wavelength from the long-wavelength CO2 laser (10.6 μm) to the mid-infrared CO laser (4.5-6.0 μm). This parameter change enables smaller hole sizes and closer spacing while maintaining drilling efficiency, directly resolving the contradiction between productivity and manufacturing precision.
2Object-affected harmful factors
If CO lasers are operated in pulsed mode to reduce thermal damage, then collateral thermal damage is reduced, but pulse rise and fall times become relatively long causing unacceptable thermal damage
Solution Approach 1:
The patent introduces an acousto-optic modulator (AOM) as an intermediary device to shape the laser pulses. The AOM precisely controls the pulse rise and fall times by modulating the acoustic wave in the crystal, enabling rapid pulse transitions that minimize thermal damage while maintaining the benefits of pulsed operation.
Solution Approach 2:
The patent dynamically adjusts the pulse characteristics (rise time, fall time, width) using the acousto-optic modulator to optimize the drilling process. By making the pulse parameters dynamic rather than fixed, the system can minimize thermal damage while achieving effective via-drilling.
3Duration of action of moving object
If acousto-optic modulator is used to clip laser pulses, then pulse rise and fall times are shortened, but beam dispersion occurs due to broad wavelength range
Solution Approach 1:
The patent introduces a dispersion compensator as an intermediary optical element to correct the beam dispersion caused by the acousto-optic modulator. This compensator realigns the dispersed wavelength components, restoring the beam focus and enabling precise via-drilling despite the broad wavelength range of the CO laser.
4Shape
If spectral bandwidth is reduced to mitigate beam spreading by AOM, then beam focusing is improved, but output power is reduced to one fifth of CO2 laser
Solution Approach 1:
Instead of reducing spectral bandwidth, the patent uses a dispersion compensator as an intermediary to correct beam spreading while maintaining the full spectral bandwidth. This approach preserves the high output power of the CO laser while achieving the necessary beam focus for precise via-drilling.
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 the creation of smaller, more densely packed via-holes with reduced collateral thermal damage, improving the efficiency and precision of the drilling process while maintaining a significant portion of the power output comparable to CO2 lasers.
Implementation Method 1
sealed off RF excited carbon monoxide (CO) laser emitting laser radiation at wavelengths in a range between about 4.5 μm and about 6.0 μm
Implementation Method 2
An AOM functions by virtue of a refractive index grating induced in a susceptible crystal such as a germanium (Ge) crystal by applying a high RF voltage to the crystal
Implementation Method 3
provides dispersion-compensation for the clipped pulses
Implementation Method 4
achromatic focusing optics for focusing the dispersion corrected pulses onto a PCB for via drilling
Implementation Method 5
MIR wavelengths have a higher absorption coefficient in PCB materials than at the longer, CO2 laser radiation wavelengths
Data Source
Figure 1
Figure 2
Figure 2A
AI summary
Apparatus for drilling a via-hole in a printed circuit board (PCB) includes a carbon monoxide laser deliver laser radiation pulses. The pulses have a relatively broad wavelength-range, and slow rising and falling edges. The rising and falling edges of the pulses are clipped using and acousto-optic modulator. A dispersion-compensator compensates for dispersion in the clipped pulses introduced by the AOM. Achromatic focusing optics focus the dispersion-compensated, clipped pulses on the PCB for the via-hole drilling.