An ISRA vision system for inspection
of photovoltaic panels |
Development of printed electronic circuits, components and finished products can be a long, meticulous and costly process. Each minute step in the production cycle is examined for performance and for flaws, and constantly adjusted. To accomplish these tasks, the manufacturer must have access to inspection equipment that will verify, beyond doubt, the integrity of the electronic structure.
Such inspection, when considered for a multi-dimensional component, is more than simply the aiming of a camera and the recording of a snapshot. It requires a system that can focus microscopically on applications in an active setting, recording the progress and flagging faults as they occur. High quality inspection means 100 percent defect detection, and is just as necessary in the development stages of a product as it is in production. The success of a product, after all, depends on its quality.
Following is a look at two companies that manufacture inspection systems for multiple industries. They have added printed electronics to their market focus because their systems are capable of examining and detecting microscopic defects, a process that can improve the quality and output of finished products.
ISRA Surface Vision
A manufacturer of inspection systems for many industries and types of materials, also is focusing on printed electronics. The company, headquartered in Germany with divisions worldwide, makes inspection equipment for use on films, foils, papers, metals, nonwovens, and plastics.
The company guarantees 100 percent seamless monitoring of a printed image via its optical inline print inspection, directly at the machine. Objective and reproducible inspection results can be achieved at production speeds of several hundreds of meters per minute. It can be used for webs, sheets, cut-outs, or blanks; on gravure, flexo, digital, or offset printing methods; as well as for flexible electronic circuits and RFID constructions.
The freely scalable inspection systems enable 100 percent monitoring and documentation of the print quality for the entire print job, and they can be implemented at any stage of the process, inline and offline. The inspection is based on coverage of the entire printed image by use of high-speed line scan cameras with high resolution.
“We have been involved in the printed electronics market for the past three years,” said Roger Matilla, account manager for print at ISRA. “Our equipment is used to inspect display panels for computers, looking for defects in glass. From there, we went into the printed electronics markets, looking for very small defects in printed applications.”
Matilla says that the company is active in the solar panel industry, in RFID, in smart cards, and wherever flexible substrates are used. “The inspection system has to have the vision capability to see down to 10 to 20 microns at production speeds,” he added. The ISRA system in use in PE, he said, is the Printstar, with modifications for the specific inspection needs.
One area in which ISRA Surface Vision is active is photovoltaics. “Thin-film solar cells are playing an increasingly important role in the photovoltaic industry. Even though the availability of the materials used for these kinds of solar cells is practically unlimited, the processing steps during the manufacturing of solar cells are still quite complicated and require that the quality process be monitored 100 percent of the time,” said Walter Meyer, marketing manager. “This is why it is a good idea to make use of a camera-based in-line inspection system after each important production segment, so it is assured that only completely inspected parts that have been found to be OK continue on to the next processing step. In doing so, the fully automated inspection with 100 percent defect recognition combined with tools for processing optimization will maximize the rate of return of the production equipment.”
The latest developments in the process, Meyer said, allow special coatings made of zinc oxide to be used for thin solar glass. “These transparent and conductive layers increase the efficiency of photovoltaic systems by nearly 5 percent. The size of the glass surfaces being produced is becoming larger, and in the generation 8.5 are reaching sizes of 2.2 m x 2.6 m. In the process, quality inspection requires particular attention to ensure that the high demands placed on the photovoltaic industry are met.”
For photovoltaics, ISRA offers the Powerscan system. It can be integrated into a variety of processing steps within the process chain. Directly after the washing sequence for the solar cell raw materials and before the high-quality coating sequence, they detect typical glass defects and specific defects such as shells and breakouts on the edges. Defective material can be discharged immediately and never reaches the high-quality coating process, Meyer said. “Powerscan is then used directly after the coating process to inspect whether the coating was applied properly. This is typically followed by the edge processing of the solar cells, which also involves an inspection process of the corners and edges. Further steps include the scribing, chemical vapor deposition, cutting and lamination processes.Each of these steps can conclude with an inspection process so that at each step only 100 percent inspected merchandise arrives for further processing throughout the entire front and back end area.”
Data and images of all significant defects are stored by the Powerscan system to be analyzed later, and can be called up during the processes with a click of the mouse. “The information collected in this way can be used for optimizing the production process,” said Meyer. “This makes it possible to ideally configure the production processes. The customers benefit from thin film solar cells of top quality.”
ImageXpert
"We came out of traditional print quality inspection, such as at Kodak, Xerox, Canon, or Epson," said Yair Kipman, president of ImageXpert, which he founded 20 years ago. "We have moved toward printed electronics because it utilizes the same technologies that we are familiar with – gravure, screen or inkjet. We use a scanner, camera or a line scan camera to capture images; we bring in the image data to our software and perform the analysis. Obviously, the analysis is different in printed electronics than in traditional printing. Here, people are interested in line width, raggedness or locating broken lines – anything that impacts the performance of conductive ink."
Over the past few years, Kipman said, the company has developed systems to analyze inks on a variety of printed materials such as plastic films, paper and solar cells. "We are doing a lot of other measurements as well, like ink volume or line height. With conductive ink it is important to know how much you are depositing since the materials are so expensive. The height relative to the background determines volume.”
The company manufactures the JetXpert for analysis of drops in flight, before it is applied to the media. JetXpert incorporates an LED strobe positioned behind jetted droplets of ink, with a camera in front to capture images of the drops in flight, which are taken in silhouette, allowing for evaluation of both translucent and opaque liquids. Single, double and triple dots can be imaged for analysis of attributes.
"Those who use inkjet technology are interested in knowing the drop size as well as the trajectory. If you are printing with an inkjet printer, the velocity of the drops may vary. When you are printing, the dot position could shift and not be as accurate as it should be," Kipman said.
ImageXpert also manufactures a full motion system for non-contact measurement of printed output. "Any printed electronics material can be put there and scanned quickly in the lab to figure out what kind of defects you might have on the sample," said Kipman. "We often use line scan camera technology for image capture, because it is very fast compared with step and repeat systems." The full motion system uses one or more cameras for image capture and ImageXpert software for analysis of many features, from dot position to edge sharpness to dimension depending on the needs of a specific application. A laser module can be added to the motion system for non-contact height measurement and 3D profiling of printing on opaque, translucent and transparent materials.
Printed electronics manufacturers have a major investment in quality, Kipman added. "They want extremely high quality control on printed material. When you are printing conductive ink, the end use is not visual. There is less of a concern about visual appearance than there is about functionality. If a line is broken, there's less of a connection. If drop speed is not what it is supposed to be, it may not be deposited in the correct location and that can cause a breakage in the line. In that respect, printed electronics is different."