THINFILM
level PV scribing. A key feature of a high throughput panel-scribing system is the use of a multi-head axis to carry the mechanical or laser scribe heads. Figure 2 illustrates this type of design. This configuration, which uses four or more scribing heads, provides much higher throughput because the number of passes required to scribe the entire panel is reduced in direct proportion to the number of heads.
Figure 2. Multi-head (step) scribe axis on a split-axis panel
scribing configuration
Machine mounting/vibration isolation, scribe-axis configuration and design, chuck design, and motion controller technology all work together to provide maximum performance and throughput. If these items are not considered the system can be plagued by problems including:
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Acceleration induced machine motion that negatively affects the dynamic straightness and dynamic straightness repeatability of the scribing tool, which ultimately affects the straightness and parallelism of the scribe lines.
Not maximizing the number of scribe heads increases processing time and scan axis duty cycle, thereby reducing scribe-tool life.
Motors that are not correctly sized for the moving mass and throughput model. Too large a moving mass on the scan axis limits peak acceleration.
Selection of a low performance motion controller that does not include throughput enhancing advanced control capabilities.
Not matching the proper axis configuration with the process objective (e.g., XY, split axis, or gantry).
Key features
For purposes of this article, the split-axis arrangement will be discussed in detail because it is the most common configuration for production-
An important part of an efficient multi-head design is the use of customizable Z axes that allow the flexibility to create exactly the configuration required and that is most efficient
This reduction of passes directly increases throughput as well as proportionately increases the life of the system. It is important to note that to properly implement a multi-head arrangement will require the motion controller to independently position these axes and, for laser scribing, trigger the lasers simultaneously. Selecting the right partner to design the motion platform and integrate the controls, drives, lasers, motion axes, and machine base is critical to addressing these issues.
An important part of an efficient multi-head design is the use of customizable Z axes that allow the flexibility to create exactly the configuration required and that is most efficient. Either direct drive or ball-screw Z stages are options, but the load and positioning requirements will be the determining factor. These axes must be configurable for the load as well as have a flexible cable management design that allows the system to integrate not only the laser scribe heads but also cameras and other elements that are needed for the system to operate as efficiently as possible.
Direct Drive
Direct-drive linear motors are used almost exclusively for a scribing tool’s primary scan axis for a multitude of reasons. For instance, high duty- cycle applications where 24/7 operation is a reality require a noncontact drive mechanism that eliminates wear and increases reliability. Other drive mechanisms such as ball-screw either cannot provide the throughput or will quickly wear-out in this strenuous environment. The inherent noncontact nature of linear motors means that they can provide precise dynamic motion, very high speeds, and a long trouble-free life.
Linear motors also can be stacked together to generate the very high forces needed for high acceleration. The design shown in Figure 3 utilized multiple linear motors stacked in parallel allowing them to generate 5 g acceleration on a 30 to 40 kg payload. The force capability of these motors was
www.solar-pv-management.com Issue III 2010
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