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Laser Marking of ECC 200 2D Matrix Codes on Printed Circuit Boards
Manufacturers of electronic devices, from home audio equipment for automotive keyless entry systems, are still looking for 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 a permanent, machine-readable code is applied to a single board to uniquely identify each product. The code must be sustainable enough to survive manufacturing processes including wave solder and board cleaning, must not affect circuit performance, and information must be stored in the small space available in real aware printed circuit boards.
The 2D matrix code provides a means to store alphanumeric strings in very small areas of the 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 well-defined high reliability of the code-codes regardless of size. Laser marking also provides the user with a computer-controlled marking process for easy implementation in automated product tracking systems.
ECC 200 2D Matrix Codes
Two-dimensional symbologies encode information in the form of a checkerboard pattern of the power 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.
· Is suitable for low contrast print directly on parts without a label
Offer · very high information density - the highest among other common 2D codes, which means you can place a lot of information in a very small area.
· They are scalable, which means that you can print and read different levels of magnification - only limited by the resolution of the printing and imaging techniques available.
· The high information density inherent in Data Matrix codes, they also offer built-in error correction techniques that allow full recovery of the message encoded in a Data Matrix symbol, even if the brand is damaged and lost as much as 20% of the symbol.
· They are read by video cameras as opposed to a scanned laser beam for reading conventional barcodes, which means that they can be read in any orientation.
Data Matrix ECC 200 is the most popular 2-D symbols with extensive use in the automotive, aerospace, electronics, semiconductor, medical devices and other production-unit-level traceability applications. Data Matrix codes usually not instead of conventional linear barcodes, but are used where traditional barcodes were too big, not enough storage, or were illegible.
Data Matrix Coding
The 2-D matrix codes are displayed as a (checkerboard) with the individual squares (cells) either on (white) or off (black) state. The code consists of four distinct elements.
· The Finder (L) The pattern consists of a solid row of cells on the left and bottom of the code that is oriented the reader to the layout of the 2D code.
• The Clock Track is a succession of power cells along the right side and top of the code the row or column count to designates the reader.
· The Data Region is the pattern of black and white blood cells in the L-pattern and clock tracks that contain the contents of the alphanumeric code.
• The Quiet Zone around the code must be free of other functions that may be visible to the reader. The quiet zone must be at least two rows / columns wide for codes constructed from square cells. The quiet zone must be at least four rows / columns wide built to codes of circular cells (dots).
ECC 200 Data Matrix codes can store up to 3116 numeric, 2335 alphanumeric characters or 1555 bytes of binary information in a 144 column by 144 row array. More realistic symbol dimensions for printed circuit boards may still contain a considerable amount information.
Laser Marking System
The laser marking consists of the laser, the beam shaping optics, and beam-steering.
The laser is a light amplifier generating a bright, collimated light beam at a specific wavelength. For FR4 and solder mask applications, most users opt for the air cooled CO2 laser in the far-infrared wavelength 10,640 nm. This laser has a number of performance and cost benefits, marking and produces excellent results.
The laser beam is projected through two beam-deflecting mirrors mounted on high speed, high precision multiplier. As the mirrors are rotated under the direction of the computer system, the laser beam scans across the target area to mark (pull) marking the desired image.
After the laser beam is deflected from the beam-levels, it is aimed the smallest spot possible flat-field focusing optics. The flat-field focusing assembly is a multi-element optical device designed for the focal plane of the focused laser beam to maintain a relatively flat surface in the marking field. The focused laser light increases the power and the corresponding marking power.
The function of the laser optical train to the focus the laser beam to a small spot and the laser beam scanning over the desired surface with high speed and accuracy. The CO2 laser configuration, the focused spot diameter and associated tag line thickness is about 0.0035 inch to 0.004 inch. Man-readable text characters can be as small as 0.040 inch and 2-D matrix codes can be constructed from individual features as small as a single 0.004 inch dot.
PCB Marking
On the occasion of circuit boards, the heat of the laser changes the surface of thermal the board to a contrasting, legible mark. The process requires no labels, stencils, punches or other supporting hardware or consumables.
For printed applications circuit board, several variations of this technique can be used for various board / coating materials and background conditions.
· Solder mask or other Conformal Coatings on FR4 Boards --
The laser beam can change the texture of the coating, making it a lighter contrasting appearance, or can completely remove the coating to expose the underlying substrate or copper base.
· Uncoated FR4 --
The laser changes the texture of the surface of the FR4 producing of a near-white appearance.
Silk-screened · Block Ink --
For users who already silkscreen component identification or other solid information on the boards, a white silk screened ink pad can function as a backdrop the 2D matrix code to optimize readability. This technique is especially useful when ...
o The background color of the board is similar to the color of the laser mark.
o underlying circuit would obscure the marking image code readers.
o The board material is not suitable for laser marking, such as ceramic substrates.
2D Matrix Code Verification
Checking the readability and the content of the 2D matrix codes is an important step in the overall quality program. After the marking of each circuit, the reader checks the integrity of the mark for indexing the laser marking head to the next marker location. The reader gets the alphanumeric string from the 2D code and compares it with the text string that must be declared.
The reader also evaluates the readability of the code based on a number of parameters including foreground / background contrast, geometric accuracy (oblique, squareness, etc.) and dimensional accuracy of both marked and unmarked cells. The 2D matrix codes are then categorized as positive (green), warning (yellow) or not (red). The total production efficiency, the laser system can be programmed to only monitor a select number of 2D codes on a panel, then automatically switch to go or all of the code and code readability below a certain level.
Today readers an excellent job reading lower contrast 2D codes. If the laser marking system is installed on a conveyor belt with older 2D matrix readers downstream of the laser marker, the reader can be configured to check the codes based on the performance of the older readers downstream evaluate to ensure consistent performance throughout the assembly process.
Tag Performance
The marker board is a typical full automated, SMEMA-compliant through-conveyor laser marking system. The overall productivity of the laser marker consists of several steps along the marking cycle. The steps necessary for a multi-panel array mark ...
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Transportation and positioning of the panel in the marking area.
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Fiducial location detection (optional)
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Marking the first circuit in the array
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Monitoring of the marked 2D matrix code (optional)
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Motion of the laser marking head to the next circuit in the array.
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Repeat steps 3 and 4 for the other circuits in the array.
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Transportation of the panel of the laser-marking system (synonymous with bringing the next panel)
Cost of measure
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 cost of utilities at maximum laser power (the laser actually should work less than 80% rated power) are $ 0.12 per hour. The primary issue is the consumer CO2 laser tube to the 3 to 5 year substituted on a typical cost of $ 1000.00 to € 1500.00. Assuming a 40-hour week and tube life of 3 years, the tube replacement cost amount to $ 0.18 per hour for a total operating cost of $ 0.30 per hour under worst case conditions. Actual costs will be lower due to fewer than maximum electrical consumption and a longer tube life.
For typical PCB laser marking applications, the cost for marking less than $ 0.0003 per circuit.
Summary
The electronics industry is seeking a cost-effective and technically efficient means of applying the machine readable codes printed circuit boards since the 1980s. Early attempts included laser marking linear barcodes on the board edge, an enormous challenge for the reader of the alignment, and marking linear bar codes next to the track circuit, a challenge for bar code readers. Barcode content was limited to a few characters because of limited space and the bar code character-per-inch capacity.
The development of the 2D matrix code in conjunction with the resolution, speed and durability of the beam-steered laser marking technology now offers manufacturers a reliable, cost-effective, flexible and verifiable means to uniquely identify each product through production, distribution and after sales service.
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