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Cutting Acrylic and Polycarbonate
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Marking 2D Codes on
Printed Circuit Boards
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Cutting Silicon Carbide Sandpaper
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SYNRAD's sealed CO2 lasers are used in a variety of industrial processes including cutting, welding, drilling, and marking. This news brief showcases some of the interesting materials and products that are processed daily by Synrad's line of CO2 lasers and marking heads.
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Cutting Acrylic and Polycarbonate
Although many types of plastics appear similar based on exterior appearance, there are often fundamental differences in their molecular structures and resulting physical characteristics. Consequently, the laser cutting behavior of various plastic materials may be very different from one another. A good example of this difference is seen when comparing acrylic (PMMA) and polycarbonate polymers. Typically, both materials look very similar with their clear, transparent surfaces; however, when cut using a CO2 laser, the results are very different.
Acrylic is a soft, plastic polymer with a simple molecular structure. Its surface exhibits a highly polished, smooth finish when exposed to heat, making it the favorite material used by sign, trophy, and award shops. On the other hand, polycarbonate is a stronger plastic polymer due to the way its molecular structure bonds together. Its increased strength and impact resistance make it a favorite material in the construction of safety enclosures and plastic lenses for eyeglasses.
To demonstrate the differences in these two plastics, a Synrad 200W laser was used in conjunction with an XY table and a cutting head outfitted with a 2.5" focal length lens that provides a 0.1 mm (0.004") focused spot size. We first cut a sheet of 3.2 mm (0.125") thick acrylic at a rate of 89 millimeters per second (210 inches per minute). Air assist at 5 PSI was used to shield the lens and reduce flaming of the acrylic vapor. The acrylic was easily vaporized without damaging the simple polymer structure bonds and the heat from the cutting process provides an excellent "flame polished" look, as seen in the first photograph.
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This Acrylic sample was cut cleanly with a "flame polished" finish using 200W of power at a speed of 210 inches per minute
This Polycarbonate sample was cut using 200W at a speed of 50 IPM. Notice the discoloration and charring of the cut edge.
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On the other hand, a sample of 3.2 mm thick polycarbonate material cuts much slower at only 21 mm/s (50 IPM). The more complex polymer structure slows the cut speed and the material chemically degrades due to numerous bonds being broken. As a result, the polycarbonate becomes charred and discolored, as seen in the second photo. Higher air pressure (90 PSI) is used to minimize charring; however, the final cut surface is still very discolored. Unfortunately, this behavior is typical for polycarbonate materials when cut by a CO2 laser. Despite its superior strength characteristics, these results must be considered when selecting a material, especially for projects where the final cut edge is visible.
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Marking 2D Codes on Printed Circuit Boards
One of the finishing steps in the PCB fabrication process is to apply a solder mask to seal out contaminants. Solder mask, a clear epoxy, can be dyed various colors, with green being the most common circuit board color. With the adoption of the RoHS Directive (Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment), some manufacturers have opted to color-code boards so that it is immediately obvious which boards are compliant and which are not.
This particular application test demonstrates the results of marking both blue and red Liquid Photo-Imageable (LPI) solder masks. LPI solder mask is widely used on circuit boards as it offers high resolution, excellent electrical properties, and compatibility with surface mount technology. Synrad CO2 lasers and FH Series marking heads can easily mark LPI solder mask without exposing the electrical traces, or otherwise damaging the board. The 10.6-micron wavelength discolors the dyed surface, which produces a highly contrasting mark.
For these samples, our marking setup consisted of an FH Series marking head, a 48 Series 10W sealed CO2 laser, and a copy of our WinMark Pro laser marking software. We created a twelve-character Data Matrix 2D code and human-readable text object in the Drawing Editor. The Data Matrix code, measuring 4 mm (0.16") square, was created with the 2D Barcode Bitmap property set to No and the 2D Barcode Circle Radius property set to 40%.
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We marked PCBs coated with blue and red solder mask using the same parameters - 10 watts of power at a speed of 12.5 inches per second in an overall cycle time of 0.40 seconds per part.
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These two properties force WinMark Pro to mark the 2D code using a vector circle (drawn at 40% of the cell size) to represent each cell instead of using the slower bitmap method where each cell is filled by scanning the beam back and forth.
On the Marking tab, we set a Power (duty cycle percentage) equivalent to 10 watts and a Velocity of 315.5 mm per second (12.5 inches/sec). For the text object, we set a Text Height of 1.9 mm (0.07") and 0.25 mm (0.01") of Extra Character Spacing to enhance readability. Power and Velocity values were set the same as the 2D Code - 10 watts and 315.5 mm/sec.
Using a 125 mm lens with a 180-micron (0.007") focused spot and a 3 mm (0.118") depth of focus, we marked both objects in a cycle time of 0.40 seconds per board. Solder mask dyes react the same to the CO2 wavelength so that only the surface layer of the PCB is affected. The mark does not penetrate this layer, leaving the continuity of the underlying copper intact.
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Cutting Silicon Carbide Sandpaper
Sandpaper is a generic term for very different types of abrasives including garnet (a naturally abrasive silica mineral), iron oxide, or synthetic materials such as aluminum oxide, silicon carbide and zirconia alumina. Depending on whether these materials are intended for manual use on a pad or sanding stick or destined for a mechanical drum, belt, or disc sander, the abrasive may be bonded to a cloth, paper, foam, or fiber backing.
What these very different combinations of abrasives and backings have in common is that they are all easily cut using a CO2 laser. The laser's obvious advantage is that its non-contact cut method is far superior to the mechanical cutting of abrasive materials. The less obvious advantage is that more and more abrasives are being pre-cut for ease of installation and use. From specialty pre-cut fan shapes for sanding sticks to the more common circular and rectangular shapes for disc, belt, and pad sanders, manufacturers are responding to the need for custom-cut abrasives to fit specific products.
To process these samples, our beam delivery setup consisted of a 63.5 mm (2.5") positive meniscus focusing lens that provides a 100-micron (0.004") spot with a 1.8 mm (0.07") depth of focus. For assist gas, we used clean, dry air at 1.4 Bars (20 PSI).
On an XY table, we cut 220-grit paper-backed silicon carbide, measuring 0.38 mm (0.015") thick, using 100 watts of power at speeds of 35.6 meters per minute (1400 inches/minute or IPM). A thicker 0.75 mm (0.0295") sheet of silicon carbide with a paper/cotton backing was cut with 100 watts at line speeds of 21.6 meters/minute (850 IPM) and we achieved speeds of 44.5 meters/min (1750 IPM) using 200 watts of power.
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220-grit silicon carbide paper cut using 100 watts of power at a speed of 1400 IPM produces clean cut edges.
This photo illustrates the laser's versatility for
cutting shapes. After importing a CAD drawing
of the required shape, we cut this sample of
0.040" thick aluminum oxide paper at a speed
of 125 IPM using 125 watts of power.
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FH Flyer / Fenix Flyer Technical Updates
Synrad Technical Updates keep you informed of recent developments related to FH Flyer Marking Head or Fenix Flyer Laser Marker products. Sign up to receive these bulletins automatically via email at http://www.synrad.com/FH_Flyer/flyersupport_subscribe.htm
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Contact Us:
Please do not reply directly to this newsletter. E-mail questions or comments to synrad@synrad.com
Synrad, Inc.
4600 Campus Place
Mukilteo, WA 98275
Tel: 1-425-349-3500
Fax: 1-425-349-3667
E-mail: synrad@synrad.com
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Copyright ©2009 SYNRAD, Inc. All rights reserved.
SYNRAD and Synrad product names are trademarks or registered trademarks of SYNRAD, Inc. All other trademarks or registered trademarks are the property of their respective owners.
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