SYNRAD, INC. - http://www.synrad.com  
Thursday, July 24, 2003
Issue 67

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 on FR4

     2-D codes are widely used in the electronics industry, thanks to their ability to pack a large amount of information into a very small space. Compared to 1-D codes, these codes feature high data density and improved readability. The 0.050" square code, marked on the circuit board in the photo to the left, consists of 10 numeric characters and is readable using a vision system. A 125 mm focusing lens (180 micron spot) directed 18 watts of  laser power at a velocity of 15 inches per second (IPS) onto the mark surface, resulting in a cycle time of 1.10 seconds.

     FR4, which has the best overall physical, thermal, and electrical properties for circuit board applications, is a flame-retardant general grade laminate created from alkali-free glass cloth coated with epoxy resin and cured under pressure and heat. In addition to providing a good substrate for text and 2D code marking, FR4 can be laser-cut, although edges typically exhibit varying levels of discoloration of charring.

A second sample, containing twelve 0.060" high alphanumeric characters, was marked using 12 W at 25 IPS in a cycle time of 0.22 seconds.

Marking Ceramic Components

    The electronics industry uses miniature surface-mount components extensively in the manufacture of circuit boards. This large (2.5 mm x 3 mm) ceramic capacitor was marked using an FH-Series marking head equipped with an 80 mm lens. Eight numeric stroke characters were marked on the face of the capacitor by the 116-micron diameter focused beam. Marking was accomplished in a cycle time of 0.35 seconds using nine watts of power at a velocity of nine IPS.

"Tip Processing" Applied to Drilling

   CO2 lasers excel at drilling small holes (small defined as less than 0.01" in diameter). Small holes are drilled directly without trepanning, resulting in reduced cycle times. Direct drilling also highlights one of the unique characteristics of lasers - the focused spot from a single laser can produce a range of hole sizes in a range of different materials.

The term"tip processing" means that only the central part of the gaussian beam is used for drilling. As the circular diameter of the gaussian beam decreases, the power density at the outer edge increases. This power density level corresponds to an effective beam diameter. Every material has a threshold of power density required for processing; below this level the material is unaffected, hence the term "tip processing".

Ultimately, the wavelength of the laser will limit how small a focused spot can be. For a Synrad laser, the 10.6 micron CO2 wavelength allows spot sizes as small as 100 microns without the addition of specialized optics. With a properly sized expander/collimator and an aspheric lens however, spot sizes down to 25-30 microns (roughly 2.5 times the CO2 wavelength) are possible. With a smaller diameter beam, power density is concentrated in a smaller area resulting in a smaller heated area.

In the case of the polyacetal nozzles, a burst or train of pulses from the laser delivered a precise amount of energy into the material. The final hole diameter depends on where that energy level matches the threshold of the material on the beam's gaussian profile. Additionally, the number of pulses, pulse duration, and pulse frequency enter into the equation. Alter the number of pulses to make small increases in hole diameter; change pulse duration and/or frequency to create larger holes. In many cases, you can hold laser power to a constant value while changing only the laser's pulsing characteristics. To produce holes larger than the spot diameter, use excessive pulse power to enlarge the hole via heat conduction. In the case of larger holes, assist gas is not required since it can disrupt the drilling process causing ragged outer edges.

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.

http://www.synrad.com/search_apps/Default.htm

To unsubscribe, please reply to this email and type REMOVE in the subject line.