Screen Printing Alignment via Pattern Offset Measurement
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Solution Overview
Problem
The existing screen printing methods for photovoltaic cells face challenges in maintaining alignment and efficiency due to screen deformation over time, leading to increased screen consumption and reduced productivity in double-layer printing processes.
Innovation Solution
A method involving the production of first and second patterns on the photovoltaic cell surface, with measurement and comparison of their positions to deduce the offset of the screen printing screen, allowing for precise alignment and correction, thereby ensuring accurate superposition of conductive layers without frequent screen changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If double-layer screen printing is used to reduce conductor resistance, then conversion efficiency is improved, but screen deformation and misalignment increase requiring frequent screen changes
Solution Approach 1:
The patent applies preliminary action by printing alignment patterns (first and second patterns) before the actual conductor printing. These patterns are printed on the substrate and screen respectively, allowing alignment measurement and correction to be performed in advance. The offset between patterns is measured and used to adjust the screen position before conducting the final conductor layer printing, thereby preventing misalignment caused by screen deformation.
Solution Approach 2:
The patent implements feedback by measuring the actual offset between alignment patterns printed on the substrate and screen, comparing it with the theoretical offset, and using this information to correct the screen position. The feedback loop involves: printing alignment patterns, measuring their positions, calculating the offset error, and adjusting the screen accordingly before final printing. This closed-loop control maintains alignment precision despite screen deformation over time.
2Productivity
If screen printing is performed at high speeds (1200 impressions per hour), then productivity is improved, but screen deformation increases leading to pattern distortion
Solution Approach 1:
The alignment patterns are printed and measured before the high-speed printing process begins. This preliminary alignment measurement and correction step ensures that the screen is properly positioned at the start of high-speed printing, compensating for any initial deformation or positioning errors that would otherwise accumulate during rapid successive impressions.
Solution Approach 2:
The feedback mechanism measures the actual positions of alignment patterns and calculates offset corrections based on the difference between actual and theoretical positions. This feedback information is used to adjust the screen position, enabling the system to maintain pattern accuracy even during high-speed operation where deformation effects are magnified.
3Manufacturing precision
If frequent screen changes are implemented to maintain alignment, then manufacturing precision is improved, but productivity and economy deteriorate
Solution Approach 1:
The continuous feedback mechanism involving alignment pattern measurement and offset correction allows the screen to be used for extended periods without replacement. By constantly monitoring and correcting for screen deformation through the alignment patterns, the system maintains manufacturing precision throughout the screen's service life, eliminating the need for frequent screen changes and associated productivity losses.
4Manufacturing precision
If alignment inspection devices are used to improve positioning accuracy, then manufacturing precision is improved, but device complexity and cost increase
Solution Approach 1:
The alignment patterns serve as intermediaries between the screen and substrate, enabling indirect measurement of their relative positions. Instead of directly measuring complex screen deformations or substrate positions, the system uses these simple printed patterns as reference markers. The patterns mediate the alignment process by providing easily detectable geometric features whose relative positions reveal the offset between screen and substrate.
Solution Approach 2:
The alignment patterns are copied onto both the substrate (first pattern) and screen (second pattern), creating identical reference features on both surfaces. This copying approach allows for straightforward comparison and offset measurement, as the same geometric patterns appear on both the stationary substrate and the moving screen, simplifying the detection and alignment process.
Data Source
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AI summary
A screen printing process for a plate (1), characterized in that it comprises the following steps: - making at least two first targets (5a - 5d) on the surface (4) of the plate (1); - Printing at least four second targets (6a - 6d), distinct from the at least two first targets (5a - 5d), during a screen printing operation on the surface (4) of the plate (1); - Measuring the actual gap obtained on the surface (4) of the plate (1) between the first targets (5a - 5d) and the second targets (6a - 6d); - Comparing this actual gap with the theoretical gap to deduce the offset of the screen printing screen (25).