Laser Diode Exposure Head for Screen Printing Stencils
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Solution Overview
Problem
Existing exposure devices for screen printing stencils, such as those using DMDs, face limitations in imaging speed due to mechanical movement of mirrors, high power consumption, and significant heat losses, which restrict their efficiency and cost-effectiveness.
Innovation Solution
The use of directly modulated laser diodes in the 300-450 nm wavelength range, controlled by digital signals, with light transmitted via fibers to a grid plate and focused through optics, eliminates the need for continuous operation and reduces power loss, allowing for higher reaction speeds and flexibility in design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If DMDs with micromechanical mirror systems are used to direct and modulate light beam, then the light output can be controlled to expose screen printing stencils, but the imaging speed is severely limited due to mechanical movement limits of mirrors (approx. 20 kHz limit frequency)
Solution Approach 1:
The patent replaces the mechanical micromirror system (DMD) with an acousto-optic modulator (AOM) that uses sound waves to diffract and modulate the light beam. This substitution eliminates mechanical moving parts, allowing for much higher modulation frequencies in the GHz range, thereby dramatically improving imaging speed while reducing mechanical complexity
Solution Approach 2:
The patent changes the operating frequency parameter from the 20 kHz limit of mechanical mirrors to the GHz range achievable with acousto-optic modulation. By using ultrasonic frequencies to create dynamic diffraction gratings in the AOM, the system achieves orders of magnitude higher modulation speeds, directly resolving the imaging speed limitation
2Power
If high-power continuous radiation sources (600-1200 watts UV) are used to provide sufficient radiation energy for exposure, then the exposure process can be performed, but power loss and heat generation increase significantly requiring special cooling
Solution Approach 1:
The patent employs pulsed laser operation instead of continuous high-power radiation sources. By delivering energy in short, intense pulses, the system achieves the required exposure energy with much lower average power consumption, eliminating the need for complex cooling systems while maintaining effective exposure capability
Solution Approach 2:
The patent changes from continuous wave (CW) operation to pulsed operation, fundamentally altering the temporal distribution of energy delivery. This parameter change allows the system to achieve high peak powers for effective exposure while maintaining low average power, thereby resolving the contradiction between required radiation energy and power loss/heat generation
3Loss of energy
If DMDs are used to modulate light beam, then the reflected away parts of light beam result in relatively high heat losses, but using laser diodes with direct modulation eliminates the need for light-deflecting mirrors and reduces power loss
Solution Approach 1:
The patent replaces mechanical mirror-based light deflection with direct electrical modulation of laser diodes. This substitution eliminates the optical path involving mirrors that cause reflective losses, directly reducing heat generation while enabling ultra-fast GHz-range modulation speeds through direct carrier injection or resonance tuning
Solution Approach 2:
The patent introduces acousto-optic modulators as intermediaries between the laser source and the stencil. These AOMs use sound waves to create dynamic diffraction gratings that modulate the light beam without mechanical mirror movement, eliminating reflective losses while achieving high-speed modulation through acoustic wave control
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 solution enhances imaging speed, reduces power consumption, and offers greater flexibility and cost-effectiveness by eliminating the need for expensive high-power light sources and complex mirror systems, enabling efficient production of both flat and cylindrical screen printing stencils.
Implementation Method 1
use of a number n of similar laser diodes working in the wavelength range of 300-450 nm
Implementation Method 2
the light signals of the laser diodes being transmitted via an equal number n of light-conducting fibers
Implementation Method 3
to direct the light output of the grid plate to a focusing optics in the exposure head that is adapted to the wavelength range of the laser diodes
Implementation Method 4
the entire screen printing stencil can be exposed according to the signals
Data Source
Figure 1
AI summary
An exposure device for producing screen printing stencils (5) has a holder (4) for the screen printing stencil (5) and an exposure system comprising at least one light source generating a light beam and optics in an exposure head (9). Furthermore, a signal source (computer) providing digital signals is present, which is connected to the exposure system in such a way that the entire screen printing stencil (5) can be exposed according to the signals. The exposure head (9) is movable relative to the screen printing stencil (5). The light source preferably consists of a number n of identical laser diodes operating in the wavelength range of 300–450 nm, with groups of laser diodes arranged in a module (12). The exposure unit typically has several such modules (12). The laser diodes can be controlled by the signals from the signal source.The light signals from the laser diodes are guided via an equal number n of optical fibers to a grid plate in the exposure head (9). The light output of the grid plate is directed to a focusing optic (10) in the exposure head (9), the wavelength of which is matched to that of the laser diodes.