High speed beam manipulation and laser controls 

Both galvanometers and polygon scanners are proven technologies for rapid beam movement.  Galvos allow rapid beam repositioning between random points in the target field, and are typically used in conjunction with a telecentric lens to deliver the light perpendicular to the target plane (e.g. PWB panel).  The latter point is most important when drilling high aspect ratio holes.

Polygon scanners are used for high speed movement of a beam along a line in the target field.  In combination with a high repetition rate laser, and part movement along the transverse axis, raster scanning of a large surface is possible.  Gating the laser on and off then permits accurate patterning of the whole field.  Applicability is generally for single-shot processes.

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Advanced optical beam delivery

Smaller beams from higher repetition rate TEA-CO₂ lasers as well as the RF- CO₂ and UV-DPSS lasers can be used in a variety of ways. Very fast beam repositioning can be accomplished over reasonable field sizes by programmable galvanometer-based mirrors and telecentric lenses. If very large panels need to be processed, the galvo beam delivery is used in combination with XY tables.

The beam from an excimer or TEA- CO₂ laser is typically rectangular in shape, with a 'top hat' intensity profile. Such beams are best utilized in parallel processing of many features simultaneously through the technique of mask imaging. The features to be produced are first generated in a metal mask, which is then placed in the beam. A lens is used to produce a demagnified image of the mask pattern, allowing very small features to be generated in the target material. Since the image is demagnified, the light intensity is increased to values well above the ablation threshold, providing very clean sidewalls in standard polymer materials. Arrays of holes can be generated by stepping and repeating this pattern. Slots can be generated by focusing the beam to a line, and translating the part underneath the beam at an appropriate speed.

Beam homogenizers have been designed to improve the utilization of these top hat beam profiles by folding in the weak edges of the beam. More sophisticated optics (holographic optical elements) are also available for the optimum beam utilization in high volume repetitive patterning applications.

High speed, high accuracy electronic test probes

In order to trim resistors to tight tolerances, high precision measurements must be made.  This needs to occur at the highest speed possible, since the probe movements and measurement times are typically much slower than the actual laser trim process.

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High speed / high accuracy motion systems 

Much of laser processing involves accurate placement of the laser beam on the part.  In order to achieve high process rates for an economically attractive production solution, the beam and part must be positioned at very high speeds so that the laser-on time is maximized.

Automated beam calibration and control

If commercially available motion control or beam control sub-systems cannot meet the accuracy demands of an application, calibration mapping can be performed to improve overall system performance.  For accuracy-critical systems, XY mapping of motion stages against a glass plate standard is a procedure performed as part of system factory calibration and test.  Z-axis mapping is also available if required.  Such mapping effectively eliminates roll/pitch/yaw issues that are present to some degree even with high-end stages.  Similarly, galvo performance can also be mapped over the galvo/scan lens field once the tables have been calibrated.  This overcomes non-linearities in the performance of the galvo/scan head combination.

Laser power can also be controlled in a couple of ways.  Power meters can be built into the system and the power routinely checked at an interval dependent on the inherent stability of the laser.  The utmost in process integrity is ensured, however, if the laser is monitored on a pulse-by-pulse basis and controlled to maintain the optimum pulse energy.  This scenario also satisfies the situation where the laser output must be varied to provide different doses to different areas of the workpiece.

Vision systems 

The ability of lasers to micromachine a variety of materials requires that the beam be positioned on the part to a high degree of accuracy.  Vision systems (e.g. CCD cameras, frame grabber cards and processing software) are commonly used to detect the presence of a part and its alignment with respect to the machine coordinate system through capture of fiducials on the part, or other recognizable feature.  If drilling a PWB panel for example, automatic compensation for translation, rotation and scaling is performed prior to commencing the drilling operation.

Further, through the appropriate choice of camera and vision processing card, vision systems can be used to compare each part or critical portion of parts to a pass/fail standard.  Parts identified as defective can then also be marked with the laser, either cosmetically or damaged so as to be functionally inoperative.  This ensures that these parts don't consume resources in downstream processing, including QC, thereby improving profitability, and removes the risk of defective parts leaving the factory, thereby reducing warranty liability. 

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Automated work handling 

Once the processing parameters have been optimized, the part load/unload time frequently becomes a noticeable factor in overall production rates.  To manage this burden, automatic load/unload of parts can be integrated into the system operation.  This automation can take many forms, depending on the part format involved.  E.g.  autoloaders for PWBs are standard accessories from a number of companies, similarly for flex panels, using vacuum pick and place.  Alternatively, parts can be transported through the workstation on a conveyor, either indexed in place for the duration of laser processing, or in continuous motion requiring part following by the laser beam delivery.  Another possibility is to have trays of parts being automatically fed into the machine.

Customized user interfaces

In a production environment, all the complexity of synchronizing beam movement, part movement and laser triggering must be handled in the background.  The sophistication of system control is interfaced to the operator through simple, clear screens on a PC running a Windows® environment.  Operator access is limited to the basic commands required to load and run a pre-set job.  Administrator access is password protected and allows creation of job files as well as service and calibration settings.  If required, alignment to fiducial marks on the panel is achieved through an integrated vision system.