Newsletter 145: Marking PCBs, Cutting Glass, Cutting Polystyrene

SYNRAD, INC. - http://www.synrad.com
Thursday, September 7, 2006
Issue 145


Marking Printed Circuit Boards	Cutting Obscure Glass	Cutting High-Impact Polystyrene

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.

Marking 2D Codes and Text 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 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 a FH Series Index head, a 48 Series 10 W 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 setup with the 2D Barcode Bitmap property set to No and the 2D Barcode Circle Radius property set to 40%.

We marked PCB’s 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.

This forces WinMark to mark the code using a vector circle 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.

Cutting Obscure Glass

Obscure glass is an industry term for textured or patterned glass that lacks transparency. Obscure glass, created by passing hot glass sheets through a set of patterned rollers, is commonly used in doors, windows, and shower enclosures to control and diffuse light for privacy as well as create a decorative look.

This application test involves cutting 4-mm thick (0.156”) obscure glass to size. Our cutting setup consisted of a cutting head driven by X-Y linear motors. We installed a 127 mm (5.0”) plano-convex focusing optic into the cutting head that provides a 182-micron (0.007”) spot with a 5.9 mm (0.23”) depth of focus. For gas assist, we supplied 4.1 Bars (60 PSI) of clean, dry air coaxially with the nozzle.

We achieved the cut quality shown in the photo using our Firestar f400 laser at a power level of 400 watts and a cut speed of 0.89 meters per minute (35 inches/min). Cut edges are clean with some underside dross.

This section of 4-mm thick textured glass was
cut at a speed of 35 inches per minute using
400 watts of power.

Cutting High-Impact Polystyrene

High-impact polystyrene (HIPS) sheet stock is used in many diverse applications. Thin sheets of polystyrene are thermoformed into appliance and computer housings. Thicker sheets are used to create display signage because the matte finish is easily printed. Polystyrene sheeting is also the material of choice for building architectural models and in fact is often used to build full-scale amusement park and movie sets.

For these cutting trials, the HIPS sheet stock measures 4.4 mm (0.174”) thick, so we setup our XY table with a 127 mm (5.0”) focusing optic that provides a 182-micron (0.007”) spot with a 5.9 mm (0.23”) depth of focus. For gas assist, we delivered 2.8 bars (40 PSI) of clean, dry air coaxially with the nozzle. The assist gas serves to keep debris off the focusing optic as well as direct molten and vaporized material down through the cut kerf.

This 4.4 mm (0.175”) thick high-impact
polystyrene sheet was cut at a speed of 68 inches
per minute (IPM) using 200 watts and at a speed
of 134 IPM using 400 watts of power.

Using a Firestar f201 laser set to a power level of 200 watts, we achieved cut speeds of 1.73 meters per minute (68 inches/min). With our f400 laser set to provide 400 watts, cut speeds increased to 3.40 meters/minute (134 IPM). In both cases, cut edges are clean and square with some melt back of the bottom edge.

Browse Synrad's Applications Database

Search our online library for more applications of Synrad's sealed CO₂ laser technology. Sort by material, process, or industry.
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Contact Us:

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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