Laser Marking Steers a New Course in Manufacturing

As the technology of laser marking has advanced, new markets have evolved to take advantage of increasingly faster marking speeds as well as greater marking precision and imaging capabilities. Continuing developments in laser-cavity design, beam-steering and focusing optics, and computer hardware and software are expanding the role of the systems.

Steering the beam

Of the available marking technologies, beam-steered laser marking systems provide users with the greatest amount of image flexibility in a fast, permanent, noncontact marking process. As manufacturing processes become more automated and after-sale tracking more prevalent, laser markers are frequently the only method available to produce individually unique, permanent images at high speed.

Beam-steered laser marking systems usually incorporate either a CO2 or Nd:YAG laser. The CO2 laser emits a continuous-wave output in the far-infrared (10.6-um wavelength) while the Nd:YAG laser emits in the near-infrared (1.06 um) in either a CW or pulsed mode (1 to 50 kHz). The Nd:YAG laser is also unique in its ability to produce very short, high-peak-power pulses when operated in the pulsed mode. For example, a typical 60-W-average-power Nd:YAG laser can produce peak powers on the order of 90 kW at 1-kHz pulse rate.

The delivery optics consist of either a simple focusing lens assembly or a combination fixed upcollimator and flat-field lens assembly. In either instance, the laser beam is directed across the work surface by mirrors mounted on two high-speed, computer-controlled galvanometers.

The simple focusing assembly offers the advantages of low cost and fewer optical components and is routinely used with CO2 lasers. The flat field lens design, though more expensive, maintains the focal point of the marking beam on a flat plane for more consistent image characteristics throughout the marking field. The flat-field lens also produces higher power density on the work surface than the simple focusing assembly due to the shorter effective focal length. The flat-field lens design is always preferred for high-accuracy and high-image-quality applications and is usually incorporated with Nd:YAG lasers.

Both designs provide the user with a selection of lenses that establish both the diameter of the marking field and the marking-line width. Longer-focal-length lenses provide larger working areas, but the line width is also enlarged, thus reducing the power density on the work surface. The user must compensate by either increasing the laser output power and/or decreasing the marking speed which usually consists of two lenses and may be placed anywhere in the beam path before the focusing lens. A beam expander often is used instead of extending the beam path approximately 10 more feet, in which the beam expands through its inherent tendency to diverge as it exits the resonator cavity. A spatial filter inserted within the beam expander produces the best mode quality in close-coupled systems, by passing the beam through a small aperture.

The last optical element that a laser beam encounters is the focusing lens. With CO2 lasers, this lens is usually made from one of several materials: Zinc selenide (ZnSe), gallium arsenide (GaAs) or germanium (Ge). ZnSe, a dense, yellow material that is transparent to visible wavelengths, is by far the most common of these materials, and it allows a low-power, HeNe laser beam through for alignment purposes. This is a great advantage over GaAs or Ge which are opaque to light from the visible portion of the spectrum.

Nd:YAG lasers almost always employ beam expansion, usually in the 2x to 5x range, because of their initially small beam diameters. Spatial filters for CO2 lasers must be external, but those for Nd:YAG lasers can be located inside the laser cavity itself, and many different sizes are available for mode selection.

Nd:YAG lasers employ optical glasses such as BK-7 or fused silica for lenses. The 1.06-um wavelength of these lasers is close enough to the visible spectrum to permit adaptation of standard optical devices with the correct AR coating to direct the laser light. For example, microscope objectives can deliver Nd:YAG laser light to the surface of VLSI circuitry for micromachining of conductor paths. As discussed earlier, delivering a Nd:YAG laser beam with fiber optics offers incredible advantages over fixed-optic delivery. The fiber advantage is unique to Nd:YAG lasers and has created an enormous growth in their use for industrial materials processing.

Fiber optic delivery for Nd:YAG

The use of fiber delivery with YAG lasers is so extensive in the industry that it should be discussed in more detail. Approximately 90 percent of new Nd:YAG welding installations involve fiber optic delivery. Because the 1.06-um wavelength is transmitted by glass optics, it can be used in standard fiber optics. Conventional beam delivery is extremely cumbersome, prone to misalignment and contamination to the optics, and can be very expensive due to custom layouts. Fiber provides a real answer to all of these problems. The benefits are:

Fibers deliver laser energy over distances which, in practice, would be impossible to achieve using conventional optics. Distances of up to 50 meters are achieved quite routinely.
Stability and accuracy are improved since only the final focus optics need to be held in an accurate relationship to the workpiece.

Most applications can be handled with standard delivery hardware (avoiding custom design).
Fibers are flexible and, within the limitations of minimum bend radius, can follow any desired route to the workpiece.

The workpiece may be held stationary while the fiber and output optics move during processing making them the ideal delivery system for use with robotic manipulation.
Fibers make the design of time and energy sharing beam distribution systems a practical possibility. The use of such systems significantly increases the flexibility and versatility of individual lasers by allowing them to address multiple workstations or produce multiple simultaneous outputs.
Access to the laser head for routine maintenance is improved since the positioning of the head is not dictated by the beam delivery system.

The low-cost fiber can be delivered to areas that are dangerous because of explosives or radiation while the laser head is located in a non-hazardous area.
Spot size at focus does not alter with changes of average power.

The optics of fiber delivery are simple and straightforward. Fiber optics used for laser delivery are typically step-index fibers. This type of fiber consists of an optically uniform core between 200 and 1500 um in diameter, surrounded by a thin cladding which has slightly different optical properties.

There are several options to fiber optic beam delivery. The first is single-fiber delivery from a single laser. This type of delivery is generally used for a dedicated production process or in development labs where moving the beam delivery to other workstations is infrequent. The choice of a single-fiber delivery is easily justified by its ease of use, ease of integration to workstations, and the capability for upgrading the system with other options in the future. Other reasons for single-fiber delivery are for robotic delivery of the laser beam and other multiaxis systems where conventional delivery would be a nightmare. With fibers, the output housing is mounted on the final-motion component so integration is incredibly economical and simple.

Another fiber delivery option is time sharing, whereby all of the laser output can be directed into any one of the several fibers on demand. A single laser with this system can provide laser energy to several different workstations switching among them at up to 40 Hz. These systems are typically used for laser welding at many different workstations, or to deliver the laser beam to separate areas of one large assembly station.

The last option is termed energy sharing. These systems divide the laser output and send the energy into several fibers at the same time. Mirrors skim portions of the beam from the laser and divert them into the input housings for each of the fibers.

The relative extent that each skimming mirror is moved into the beam path determines the sharing ratio. Typical energy-share systems can split the beam into as many as four fibers. These systems are used to weld many parts simultaneously, in order to increase throughput, or to eliminate the part distortions that often result from sequential welding of a single assembly.

The system computer creates marking images by sending beam-motion signals to the galvanometer drivers while simultaneously blanking the laser beam between marking strokes. The motion of the galvanometer-mounted mirrors directs the marking beam across the target surface much like a pencil on paper to draw alphanumeric and graphic images.

Laser selection

Laser marking uses the high power density of the focused laser beam to generate heat on the work surface and induce a thermal reaction. A readable, contrasting line is produced by increasing the target surface to annealing temperatures, the melting point or to vaporization temperatures. Annealing and melting are employed to induce a contrasting color change on a wide variety of metallic's as well as plastics, ceramics and other nonmetallic's. The fastest marking speeds are obtained by increasing the temperature to the vaporization point to engrave metallic's and many nonmetallic's.

The near-infrared wavelength of the Nd:YAG laser is well suited to most metallic's and many plastics. The Nd:YAG can anneal or melt in both the CW and pulsed mode and can provide the necessary peak pulsed power to engrave. With many materials, the Nd:YAG can simultaneously engrave the surface and induce a contrasting color change in the engraved trough.

The far-infrared wavelength of the CO2 laser is compatible with plastics, ceramics and organic materials. However, without the high-peak-power capability required to achieve vaporization temperatures, the CO2 laser is limited to annealing or melting the surface.

Advantages

Beam-steered laser marking offers several advantages over other marking methods. Most apparent is the unique combination of speed, permanence and the flexibility of computer control. Although other technologies can provide one or two of these attributes, no other method offers all three to the same degree.

Many users also benefit from the noncontact nature of laser marking. The only force applied to the part during the marking cycle is the very localized thermal effect of the laser beam. No additional physical force is applied, with the exception of any appropriate part-handling motion designed into the system. Silicon wafers, silicon disk drive read/write heads and many medical devices are examples of components that are too fragile for any type of mechanical marking. In addition, laser marking provides the permanence necessary to satisfy image-lifetime requirements, while printed marking does not.

Laser-marking systems also excel at creating intricate graphic images. Nd:YAG lasers can produce marking-line widths on the order of 0.001 inch or less, which, when combined with marking resolution of 0.0002 inch/step, can produce images with much more detail than mechanical contact or stencil systems.

Regardless of the specific process justifications for incorporating laser marking, the application of the technology can result in significant cost savings. With operating costs for the Nd:YAG system, users have reported cost savings of greater than 90 percent and associated reductions in quality control and inventory expenses.

As manufacturing industries continue to automate their manufacturing processes, incorporate aftershipment traceability, reduce manufacturing cycle times, apply more sophisticated graphics and develop products requiring new marking techniques, the laser-marking manufacturers will continue to improve the power, speed, image-generation capabilities and user-friendliness of their products.

Richard Stevenson is the Sales Director for Control Micro Systems, Inc. a manufacturer of beam-steered laser marking systems. He has published and presented numerous technical papers and articles on laser marking in trade publications. For information on Plastic Welding, Engraving, Cutting, Etching or Marking call 407-679-9716 or email sales@cmslaser.com

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Understanding Laser Marking and Laser Etching Systems

Laser marking and laser etching are becoming more and more important in a growing number of industries. The basic reasons to laser marking or laser etch your products include:

o The mark is extremely durable, permanent and in most cases cannot be removed without destroying the product itself, this is true for laser marking, laser etching, or laser annealing.

o The laser marking process is accurate, 100% repeatable, fast, with very clear sharp results.

o The laser mark or laser etch can quickly and easily be changed without any machine change over, and, without replacing any tools. The changing of a laser marking or laser etch is a simple drag and click computer operation.

o The laser requires no consumables and no additional purchases of added materials or supplies. Therefore the operating and maintenance costs of owning and running the laser marking or laser etching system are virtually non existent.

Laser Basics

The word laser is an acronym for light amplification by simulated emission of radiation. The laser beam is formed in a sealed tube with an electrode set, laser gas, and electrical discharge. The beam is emitted into a telescope which expands the laser beam from a size of approximately 2mm as the beam exits the laser tube up to 7mm to 14 mm for most laser marking or laser etching operations. The expanded beam is directed into a laser head containing two mirrors located on high speed galvo motors. The laser beam is directed off the mirrors though a single element flat field lens to the product being laser marked or etched.

Typically the laser marking or laser etching fields created range in size from 65mm x 65mm [2.5" x 2.5"] at the smallest size to 356mm x 356mm [14.0" x14.0"] square at the largest. The next consideration is the laser beam spot size. This is the size of the focused laser light energy at the laser marking or laser etching point on the product and can vary from approximately 200 micron [micrometers] or .0078" at the smallest to approximately 540 microns or .021" for Co2 lasers. The laser beam spot size ranges from approximately 20 microns or .0007" at the smallest to approximately 70 microns or .0027" at the largest for Nd:YAG lasers. These small spot sizes and highly focused laser light energy create the detailed, clear, permanent marking that is typical of the laser marking or laser etching process.

Controlling Lasers and Laser Marking Options

Laser markers and laser etchers are controlled via software. Several variables need to be controlled:

1. Laser power as measured in watts

2. Frequency, meaning the pulse frequency of the laser beam

3. Inches per second, meaning the speed that the beam steering mirrors are moving

Determining the correct setting for the laser is the single most important and critical element in the success or failure of the laser marking process. Once the proper settings have been determined and demonstrated a 100% repeatable laser mark can be achieved.

Laser controller software is accessed via a PCI interface card. This sends the digital signals of the computer based marking or etching files to the motors and directs the laser beam to the product being laser marked or laser etched.

There are several different types of laser marking and laser etching and several different considerations in terms of visual results for the laser mark or laser etch.

1. Laser etching produces a visible etching or depression into the material. Laser etching replaces traditional process like mechanical press or pin scribing. Laser etching can be done with either a Co2 or YAG laser on virtually any material surface and to any depth from very light etching to very deep etching. For example, laser etching is used to engrave serial numbers into metal gun frames. Generally speaking with laser etching the material being laser etched is vaporized at the laser etching point due to the typically high power densities of the laser beam at the point of laser etching.

2. Laser marking produces a surface mark with very little engraving and very little disruption of the material surface. This is especially useful in certain industries such as discrete electric components, semi-conductor, electrical fuse, and ceramics where laser etching can actually damage part or change the conductive qualities of the part. Generally in order to produce the laser mark without deep engraving a high speed per inch setting for the galvo head is used.

3. Laser etching and laser marking generally do not produce any color changes and create a colorless impression. There are exceptions as certain plastics will sometimes react to and change color under either Co2 or YAG laser light. Also, in some cases, additives can be incorporate into the materials being laser marked or laser etched in order to produce a color change. Another exception occurs when the wavelength of either the Co2 or YAG laser is changed from those typically used in laser etching and laser marking. This can produce a color change after laser etching on some materials.

4. Laser annealing is another popular form of laser marking. This type of laser marking is generally undertaken with a YAG laser on metal surfaces using lower power, high frequency and slow writing speeds to produce heat on the surface of the product. Laser annealing can be used to replace electro chemical etching and ink marking as the laser annealing process creates a black mark with no etching. Care must be used, as the heat generated can cause iron in some metals to be pulled to the surface, and rust can result if the parts are subjected to sterilization after laser annealing. This can be an especially difficult issue for medical devices

5. Laser ablation is also a popular use for laser marking systems. In this case the laser is used to remove a layer of paint, anodized or some other material covering the surface of the part. For example this process is used to create bear metal contact points on a painted part, to allow battery connection as in cell phones, or to remove paint for identification of parts and manufacturer details.

Jim Morin writes for Worldwide Laser a company that specializes in Co2 and YAG marking systems used in a wide range of applications. For more information visit http://www.wlsc.com

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Beam-Steered Laser Marking of Plastics

Beam-steered Nd:YAG (Neodymium:Yttrium Aluminum Garnet) laser marking provides a unique combination of speed, permanence, and imaging versatility in a noncontact marking process. Laser marking can generate considerable savings in reduced manufacturing and tooling costs; elimination of secondary processes and consumable disposal; and reduced inventory expense, quality-control costs, and maintenance downtime. Laser marking frequently improves the aesthetic appearance of the marking image, thereby increasing the product's perceived value.

Of all materials, plastics are the most challenging in terms of the laser's interaction with the material and the required image quality. The wide variety of material chemistries and colors and the aesthetic requirements of most plastics applications require special consideration in both material chemistry and imaging techniques. The successful implementation of laser marking technology requires a working knowledge of the laser marker's function and capabilities and a committed, team approach by the user.

Marking Fundamentals

Laser marking is a thermal process that employs a high-intensity beam of focused laser light to create a contrasting mark on the material surface. As the target material absorbs the laser light, the surface temperature increases to induce a color change in the material and/or vaporization of material to engrave the surface.

Beam-steered laser marking employs mirrors mounted on high-speed, computer-controlled galvanometers to direct the laser beam across the target surface. Each galvanometer provides one axis of beam motion in the marking field. A multi-element, flat-field lens assembly subsequently focuses the laser light to achieve high power density on the work surface while maintaining the focused-spot travel on a flat plane. The laser output is gated to blank the beam between marking strokes.

Marking can be accomplished at speeds of up to 5000 mm/sec with positioning speeds between marking strokes of 50,000 mm/sec. Because the process relies on heat conduction into the plastic, marking speeds are usually slower than the system's maximum capability to allow sufficient conduction to achieve the desired results.

The beam-steered marker can duplicate virtually any black-and-white image, including variable line widths and images as small as 0.0001 inch. Present computer-imaging technology produces highly intricate graphics with line widths, resolution, and accuracy well below 0.001 inch. Because the image is created by "drawing" with the laser beam, the marking time is dependent on the amount and complexity of the text and graphics. With computer-generated imaging, any graphic element or the entire marking program can be instantly changed before a new part is positioned for marking.

Nd:YAG lasers amplify light of 1.06mm wavelength in the near-infrared. They are unique among the different types of lasers in that they operate much like an "optical capacitor." In pulsed operation, the Nd:YAG laser stores energy between pulses, resulting in peak powers of kilowatts of light energy. A Nd:YAG laser emitting 75 watts of continuous light, pulsed at 1 kHz, emits a train of pulses with peak powers of 110,000 watts. The "optical capacitor" effect provides the peak power necessary to vaporize material. For plastics applications, the laser must also be run in a "top hat" mode, where the power distribution is fairly even across the cross section of the laser beam in order to eliminate "hot spots" in the marking path.

The beam-steered Nd:YAG marker frequently replaces acid and electro-etch systems, stamping and punching systems, and those other marking systems that permanently mark products by imprinting or engraving. It also replaces other, less permanent printing systems, including ink jet.

Uncoated Plastics

Most uncoated plastics must be doped with a material reflective to the laser wavelength to prevent over-absorption of the laser light, which results in loss of control of the temperature rise and excessive melting on the surface. Light-colored plastics are doped with mica, titanium dioxide or carbon-containing materials. The heat generated by absorption of the laser light causes the carbon to migrate to the surface, producing a contrasting dark mark against the unaltered background plastic.

Plastics are semitransparent to the near-infrared wavelength of the Nd:YAG laser. Depending on the degree of transparency and the laser output power, the laser beam can alter the material surface to depths of more than 0.025 mm without achieving vaporization temperature on the surface. If material vaporization occurs, the layer of carbon is thinned and the marking image will appear washed out.

There has been considerable success in altering the depth of carbon migration to create gray-scale graphics on light plastics. Adjusting the power and/or pulse rate of the laser controls the depth of penetration and therebv the darkness of the mark. Increasing the laser power will increase the overall depth of penetration and thickness of the carbon layer. Increasing the pulse rate will result in a longer pulse width and lower peak power. The longer exposure also increases the depth of penetration and associated carbon layer.

Dark plastic is doped with a material that produces a lighter color as the material expands and the density decreases. As the temperature of the plastic increases, the plastic expands to form a "blister" on the surface and a lighter-colored mark. As with light plastics, the temperature must be tightly controlled to avoid over absorption. If the temperature rises too high and the blister bursts, material is lost and the mark will lose contrast.

Not all plastics require dopant to achieve a contrasting mark. Several plastics do yield excellent results without additives; for example, most black polycarbonates produce a snow-white mark without altering the chemistry.

Coated Plastics

Coated plastics consist of a solid, translucent, or transparent plastic with one or more coats of ink or paint. The marking image is created by achieving vaporization temperature on the surface to remove the top coat and expose the underlying plastic or second coat.

Coated plastics allow a great deal of control over color selection and marking contrast. Transparent plastics allow the designer to use an underlying part to establish the background color (marking image) while the top coat determines the foreground color. Solid plastics establish their own background with the color of the plastic. Translucent plastics are frequently used for back-lit applications. The plastic is initially coated with a white paint and overlaid with a dark top coat. The laser removes the top coat, exposing the white paint for daytime visibility. When the part is back-lit at night, the lighting illuminates the translucent plastic from behind and the marking image appears in the color of the plastic.

The paint or ink used must be conducive to laser processing. Standard paints and inks are neither predictable nor controllable when exposed to the laser output. The inks burn easily and can mix with the underlying plastic while in the molten liquid state. Laser-compatible inks are mixed with a silicone-based material reflective to the laser output, thereby reducing the ink's light absorption and rate of thermal reaction. Paints must be suitable for high-temperature processing and be free of any contaminants that may absorb the laser wavelength and speed up the thermal rise.

To achieve a quality image, the top coat must be completely removed with minimal impact on the underlying plastic or secondary coat. To maximize the ratio of light absorption between the two layers, the top coat must always be a dark color and the contrasting underlying layer must be a light color. The dark color will absorb a comparatively higher percentage of the laser light, resulting in a higher surface temperature, while the light color reflects a higher percentage and minimizes the temperature rise. The underlying plastic, paint, or ink should also be thick enough to tolerate a minor amount of material removal during marking.

Marking coated plastics is a multi-step process in which the first marking pass removes the majority of the top coating. The remaining residue is removed with a second, lower-power pass to minimize the effect to the underlying material. For precise edge definition, the outline of the image is marked prior to filling in the image. The outline is marked with a heavy edge pass (i.e., 50 kHz, 250 mm/sec, 2.5 watts) followed by a lower-power cleanup pass (50 kHz, 250 mm/sec,1.75 watts). The image is then filled, if desired, with a heavy fill pass (50 kHz, 650 mm/sec, 6 watts) and subsequent cleanup pass (50 kHz, 6.50 mm/sec, 4.5 watts). Care in determining the process parameters for each pass and the edge and fill beam paths will result in a crisp, high-contrast, high-quality marking image.

Preparation and Installation

Perhaps the most critical element in the successful application of laser marking is the composition of the part programs. When replacing an existing marking technology, one must allow up to six months for conversion of existing art work to part-marking computer programs. Even if the present artwork resides in AutoCAD files, time must be allotted to convert the files to optimized marking programs.

Many users start with thousands of sheets of Mylar artwork. (Mylar is a DuPont trade name.) Each Mylar film is scanned to create a bitmap image. The scanned bitmap could be directly converted to the laser marker format with good image quality, but the cycle time would be unnecessarily long, with excessive marking line overlap.

For best results, import the scanned bitmap into AutoCAD as a positional template. Create a separate marking "logo" for each alphanumeric character and graphic image, and, in AutoCAD, place each logo in position on a separate layer, using the bitmap template as a positioning guide. A library of optimized logos facilitates the creation of programs from the scanned artwork, allows nonstandard text kerning and line leading, and ensures low cycle time and high image quality. After all the logos are in place, the template layer is removed, and the final CAD file is converted to the laser marker program format.

If the art work already exists in a CAD file format, the image elements could be optimized without using a separate library of logos. Every element including repetitive elements shared between drawings must be individually optimized. It will take considerably longer to convert large quantities of files, and there is no guarantee that every clement is optimized correctly. It is far more efficient to use the original AutoCAD file as the placement template for optimized logos.

Implementation of beam-steered laser marking requires a team effort. With cooperative implementation. manufacturing can ensure product flow and integration with existing controls, the materials department ensures that plastics and coatings are appropriate for laser marking, and engineering will produce part-marking programs with low cycle times and high-quality images. Careful team planning, preparation, and execution will result in a smooth application of laser marking technology and the associated benefits in manufacturing efficiencies, quality, and product value.

Richard Stevenson is the Sales Director for Control Micro Systems, Inc. a manufacturer of beam-steered laser marking systems. He has published and presented numerous technical papers and articles on laser marking in trade publications. For information on Lazer Welding, Engraving, Cutting, Etching or Marking call 407-679-9716 or email sales@cmslaser.com

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Laser Marking of ECC 200 2D Matrix Codes on Printed Circuit Boards

Manufacturers of electronic devices, from home audio equipment to automotive keyless entry systems, are increasingly seeking a reliable, cost effective method for uniquely identifying and tracking products through the manufacturing cycle, sales distribution and after-sale warranty verification. An autonomous, automated tracking system requires that a permanent, machine-readable code be applied to an internal printed circuit board to uniquely identify each product. The code must be durable enough to survive manufacturing processes including wave solder and board cleaning, must not affect circuit performance, and must store information in the small space available on real-estate conscious printed circuit boards.

The 2D matrix code provides a means to store alphanumeric character strings in very small areas of the printed circuit board. Laser marking technology provides a method for permanently applying 2D matrix codes to most board substrates. The high-resolution and high-accuracy of beam-steered laser marking systems provides the means to create well defined, high reliability codes regardless of code size. Laser marking also provides the user with a computer-controlled marking process for easy implementation into automated product tracking systems.

ECC 200 2D Matrix Codes

Two-dimensional symbologies encode information in the form of a checkerboard pattern of on/off cells. Specific advantages of Data Matrix codes over conventional 1D barcodes include:

· Encode information digitally, as opposed to the analog encoding of data in conventional barcodes.

· Can accommodate low-contrast printing directly on parts without requiring a label

· Offer very high information density - the highest among other common 2D codes, which means that you can place a lot of information in a very small area.

· They are scaleable, which means that you can print them and read them in various levels of magnification - only limited by the resolution of the available printing and imaging techniques.

· Due to the high information density inherent to Data Matrix codes, they also offer built-in error-correction techniques which allow fully recovering the message encoded in a Data Matrix symbol even if the mark is damaged and missing as much as 20% of the symbol.

· They are read by video cameras as opposed to a scanned laser beam used for reading conventional barcodes, which means that they can be read in any orientation.

ECC 200 Data Matrix is the most popular 2-D symbology with extensive use in automotive, aerospace, electronics, semiconductor, medical devices and other manufacturing unit-level traceability applications. Data Matrix codes are typically not replacing conventional linear barcodes, but are being used where traditional barcodes were too large, did not provide sufficient storage capacity, or were unreadable.

Data Matrix Code Structure

The 2D matrix codes appear as a "checkerboard" with the individual squares (cells) in either on on (white) or off (black) state. The code consists of four distinct elements.

· The Finder "L" Pattern consists of a solid row of cells along the left edge and bottom of the code that orients the reader to the layout of the 2D code.

· The Clock Track is a sequence of on/off cells along the right edge and top of the code that designates the row/column count to the reader.

· The Data Region is the pattern of black and white cells within the L pattern and the clock tracks that contain the alphanumeric content of the code.

· The Quiet Zone around the code must be free of any features that may be visible to the reader. The quiet zone should be at least two rows/columns wide for codes constructed of square cells. The quiet zone should be at least four rows/columns wide for codes constructed of circular cells (dots).

ECC 200 Data Matrix codes can store up to 3,116 numeric, 2,335 alphanumeric characters or 1,555 bytes of binary information in a 144 column by 144 row array. More realistic symbol dimensions for printed circuit boards can still contain a significant amount of information.

Laser Marking System

The laser marking system consists of the laser source, the beam-shaping optics, and the beam-steering system.

The laser is a light amplifier generating a bright, collimated beam of light at a specific wavelength. For FR4 and solder mask applications, most users choose the air-cooled CO2 laser operating at the 10,640nm far-infrared wavelength. This laser offers several performance and cost advantages, and produces excellent marking results.

The laser beam is projected through two beam-deflecting mirrors mounted to high-speed, high-accuracy galvanometers. As the mirrors are rotated under direction of the system computer, the laser beam scans across the target marking surface to "draw" the desired marking image.

After the laser beam is deflected from the beam-steering mirrors, it is focused to the smallest spot possible by flat-field focusing optics. The flat-field focusing assembly is a multi-element optical device designed to maintain the focal plane of the focused laser beam on a relatively flat plane throughout the marking field. The focused laser light significantly increases the power density and associated marking power.

The function of the laser optical train is to focus the laser beam to a small spot and to scan the laser beam over the target surface with high speed and accuracy. With the CO2 laser configuration, the focused spot diameter and associated marking line width is about 0.0035" to 0.004". Man-readable text characters can be as small as 0.040" and 2D matrix codes can be constructed from individual features as small as a single 0.004" dot.

PCB Marking

To mark printed circuit boards, the heat generated by the laser beam thermally alters the surface of the board to create a contrasting, legible mark. The process does not require labels, stencils, punches or any other auxiliary hardware or consumable.

For printed circuit board applications, several different variations of this technique can be used for different board/coating materials and background conditions.

· Solder mask or other Conformal Coatings on FR4 Boards -

The laser beam can alter the texture of the coating, giving it a lighter contrasting appearance, or can completely remove the coating to expose the underlying substrate or copper ground plane.

· Uncoated FR4 -

The laser beam alters the texture of the surface of the FR4 producing a near white appearance.

· Silk-screened Ink Block -

For users who already silkscreen component identification or other fixed information on the boards, a silk-screened white ink block can function as a background to the 2D matrix code to optimize readability. This technique is particularly helpful when...

o The background color of the board is similar to the color of the laser mark.

o Underlying circuitry would obscure the marking image to code readers.

o The board material is not suitable for laser marking, such as ceramic substrates.

2D Matrix Code Verification

Verification of the legibility and content of the 2D matrix codes is an important step in the overall quality program. After marking of each circuit, the reader verifies the integrity of the mark before indexing the laser marking head to the next marking location. The reader retrieves the alphanumeric text string from the 2D code and compares it with the text string that was to be marked.

The reader also evaluates the legibility of the code based on a variety of parameters including foreground/background contrast, geometric accuracy (skew, squareness, etc.) and the dimensional accuracy of both the marked and unmarked cells. The 2D matrix codes are then categorized as passed (green), warned (yellow) or failed (red). For overall production efficiency, the laser system can be programmed to verify only a select few 2D codes on a panel, then to automatically switch to verifying every code if the code legibility falls below a specified level.

Today's readers do an excellent job reading lower contrast 2D codes. If the laser marking system is installed on an assembly line with older 2D matrix readers downstream from the laser marker, the verification reader can be configured to evaluate the codes based on the performance of the older downstream readers to assure consistent performance throughout the assembly process.

Marking Performance

The typical printed circuit board marker is a fully automated, SMEMA-compliant, through-conveyor laser marking system. The overall productivity of the laser marker is comprised of several steps that make up the marking cycle. The steps required to mark one multi-array panel are...

1. Transport and positioning of the panel in the marking area.

2. Fiducial location detection (optional)

3. Marking of the first circuit in the array

4. Verification of the marked 2D matrix code (optional)

5. Motion of the laser marking head to the next circuit in the array.

6. Repeat steps 3 and 4 for the remaining circuits in the array.

7. Transport of the panel out of the laser marking system (synonymous with bringing the next panel in)

Cost of Operation

Cost of operation is much less than $1.00 per hour. Typical utilities requirements are 110VAC, 1-phase, 12A. A compressed air source is required for the pneumatics. Total utilities costs at maximum laser power (the laser should actually operate at less then 80% rated power) are $0.12 per hour. The primary consumable item is the CO2 laser tube that must be replaced every 3 to 5 years at a cost of typically $1,000.00 to $1,500.00. Assuming a 40-hour workweek and tube life of 3 years, the tube replacement cost would equate to $0.18 per hour for a total operating cost of $0.30 per hour under worst case conditions. Actual operating costs will be lower due to less than maximum electrical usage and longer tube life.

For typical pcb laser marking applications, the cost for marking is less than $0.0003 per circuit.

Summary

The electronics industry has been searching for a cost and technically effective means of applying machine-readable codes to printed circuit boards since the 1980's. Early attempts included laser marking linear barcodes on the board edge, a daunting challenge for reader alignment, and marking linear barcodes next to circuit traces, also a challenge for barcode readers. Barcode content was limited to a few characters due to limited space and the barcodes character-per-inch capacity.

The development of the 2D matrix code combined with the resolution, permanence and speed of beam-steered laser marking technology now offers manufacturers a reliable, cost-effective, flexible and verifiable means to uniquely identify every product through production, distribution and after-sale.

Visit Laser Marking or call (407) 679-9716

© 2006 by Control Micro Systems, Inc. Free for unlimited distribution as long as this copyright notice and link to web site are in place.

Richard Stevenson is the Sales Director for Control Micro Systems, Inc. a manufacturer of beam-steered laser marking systems. He has held numerous engineering, sales and marketing positions since joining the laser industry in 1976. He has published and presented numerous technical papers and articles on laser marking in trade publications and conferences and has represented the laser marking industry on the Laser Systems Product Group of the Association of Manufacturing Technology.

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How Industries Increase ROI By Using Fiber Laser Marking For The Imaging Process

Most laser marking techniques involve either engraving the mark into metal or plastic components, or ablating a surface layer to reveal a contrasting material underneath. Both processes usually require high energy pulsed laser systems and of course involve process debris.

Fiber lasers are now a robust industrial tool with a unique series of capabilities that enable a wide range of precision materials processing manufacturing methods. Fiber lasers offer low running costs, a fast ROI, a small footprint and exceptional reliability, and are thus enjoy a growing acceptance within the laser-assisted manufacturing industry as a cost-effective alternative to conventional laser design.

Laser marking is able to generate high contrast, easily readable and durable identification on a wide variety of components for industrial use or consumer products. Computer generated vector or bitmap patterns (logos, barcodes or text) can be engraved or etched using a non-contact process onto metallic and nonmetallic materials, including metals, plastics, glass, electronics, PCBs, wafers, medical devices, sporting goods and packaging.

A combination of a reliable industrial laser, fast and accurate galvanometric imaging systems and convenient computer control provides manufacturers with a unique combination of speed, permanence and versatility that cannot be matched by any other marking technique.

Laser marking processes

Traditionally, laser marking involves either engraving a physical mark onto a surface just as for traditional engraving methods, generating a simple color change in surface, or etching of a surface layer of material to reveal another, highly contrasting layer underneath. Either technique can be used on a broad spectrum of materials, and in addition to generating identifying marks can also form part of an industrial process, for example in electronics manufacture.

The advantages of laser marking include speed, flexibility and the non-contact marking process, meaning that components parts are not stressed by the marking process. The non-contact nature of the process also contributes to low maintenance schedules, as tools do not need to be replaced. Additionally laser marking is also highly repeatable and easily readable (even machine readable).

Stringent Quality Control

A laser engraving process is often used for marking metal surfaces as it is swift, non contact and extremely durable, but is however also responsible for the production of debris - fine metallic particles removed from the surface as part of the engraving process.

Naturally for bearing manufacture there are stringent requirements for process debris. The marking of bearing housings using a laser has thus traditionally combined a "minimal" engraving process with an induced change in surface color. CMS had until recently accomplished this using Nd:YAG lasers, but customer demand was looking for a way around the cost, maintenance, lifetime and reliability issues associated with the Nd:YAG design.

For this application CMS engineers have pioneered the use of a fiber laser from SPI Lasers plc of Southampton, UK - more specifically a 100 W cw/modulated fiber laser usually used for welding and cutting tasks. SPI has been developing fiber lasers for the industrial market for several years, primarily for materials processing applications such as microwelding and microcutting, but also for marking applications.

Switching to the new fiber laser means generating the same thermally induced high contrast mark on the bearing housing, but doing so with less production of debris, at reduced raised recast, and at much greater convenience to the end-user - meaning almost no maintenance, increased lifetime and exceptional reliability.

The 100W fiber laser used in this application typifies the flexibility of fiber lasers as a tool for a wide variety of applications - marking applications are traditionally an application for high energy pulsed lasers, but the performance envelope provided by fiber laser technology allows systems integrators like CMS to redefine these domains.

Advantages of fiber lasers

Many different laser designs have found their way into materials processing applications. Fiber lasers are however revolutionizing many of these applications through a combination of improved optical performance, better system flexibility, high component yield, long up-time and exceptional reliability.

Critical to many marking applications, they do not exhibit the shortcomings in spot size performance found in other laser designs - at all power levels, across all pulse sequences and during the entire lifetime of the laser, the spot size remains small, predictable and consistent.

The small spot size and high beam quality also mean high irradiance at the focus, so manufacturing tools equipped with fiber lasers can produce better results faster and at lower power levels. The focused beam consistently treats only a very small area of material, with the benefit that very little heat is generated in the surrounding area. High quality precision marking, welding and cutting can be performed close (0.1 mm) to the most complicated and intricate component parts.

Factoring in the reliable operation and power modulation flexibility, fiber laser technology is now frequently chosen as an upgrade over conventional flash-lamp pumped solid state, or even DPSS laser technology in many other laser-assisted industrial manufacture segments. The consistent and improved marking performance means reduced maintenance costs, longer up-times and improved production quality with less scrap. Fiber lasers are also exceptionally physically robust and thus suitable for the most challenging of industrial environments.

All of these factors equate to a plug-&-play, maintenance-free architecture for systems integrators looking to cut development, production and servicing costs, with the added benefit of being able to provide the end user with a better, more flexible product. Last but not least, the end user will be able to focus on their business demands rather than having to become laser maintenance experts.

Advantages for industrial manufacturers

In general, the choice of tooling for any application comes down to determining the required performance followed by a trade-off between initial outlay, component yield, uptime and maintenance.

Not only are component assemblies becoming increasingly more complex but, at the same time, more and more demands are being placed on their quality and functionality. The deployment of manufacturing tools equipped with fiber lasers to enhance process control can thus bring important financial advantages for any manufacturer. Coupled with the small footprint, such tools can also open up processes that were previously out of reach for some manufacturers.

Richard Stevenson is the Sales Director for Control Micro Systems, Inc. a manufacturer of beam-steered laser marking systems. He has published and presented numerous technical papers and articles on laser marking in trade publications. For information on Laser Drilling, Engraving, Cutting, Etching or Marking call 407-679-9716.

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