Manufacturers of electronic devices, from home audio equipment to keyless entry systems for automobiles, are increasingly looking for a reliable and cost-effective method to uniquely identify and track products through the manufacturing cycle, sales distribution and after-sales warranty verification. A self-contained and automated tracking system requires a permanent machine-readable code to 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 soldering and board cleaning, it must not affect circuit performance, and it must store information in the small space available on self-conscious printed circuit boards. the real estate.
2D matrix code provides a means of storing strings of alphanumeric characters in very small areas of the printed circuit board. Laser marking technology provides a method to permanently apply 2D matrix codes to most plate substrates. The high resolution and high precision of beam-directed laser marking systems provide the means to create well-defined and highly reliable codes, regardless of code size. Laser marking also provides the user with a computer controlled marking process for easy implementation in automated product tracking systems.
2D ECC 200 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, unlike analog encoding of data in conventional barcodes.
Can accommodate low-contrast printing directly on parts without the need for a label
Offer a very high information density, the highest among other common 2D codes, which means that you can put a lot of information in a very small area.
They are scalable, which means you can print and read them at various levels of magnification, only limited by the resolution of available printing and imaging techniques.
Due to the high information density inherent in Data Matrix codes, they also offer built-in error correction techniques that allow the message encoded in a Data Matrix symbol to be fully recovered even if the mark is damaged and up to 20% of the symbol is missing. .
They are read by video cameras rather than a scanned laser beam that is used to read conventional barcodes, which means 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, semiconductors, medical devices, and other manufacturing unit-level traceability applications. Data Matrix codes do not normally replace conventional linear barcodes, but are used where traditional barcodes were too large, did not provide enough storage capacity, or were unreadable.
Data matrix code structure
2D matrix codes appear as a “checkerboard” with the individual squares (cells) in an on (white) or off (black) state. The code consists of four different elements.
· The Finder’s “L” pattern consists of a solid row of cells along the left edge and bottom of the code that guides 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 for the reader.
The data region is the black and white cell pattern within the L pattern and the clock tracks that contain the alphanumeric content of the code.
The quiet area around the code should be free of any features that may be visible to the reader. The quiet zone must be at least two rows / columns wide for codes built with square cells. The quiet zone must be at least four rows / columns wide for codes constructed with circular cells (dots).
ECC 200 data matrix codes can store up to 3116 numeric characters, 2335 alphanumeric characters, or 1555 bytes of binary information in a 144 column by 144 row matrix. The most 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 that generates a bright, collimated beam of light at a specific wavelength. For FR4 and welding mask applications, most users choose the air-cooled CO2 laser that operates at a far infrared wavelength of 10,640nm. This laser offers several performance and cost advantages and produces excellent marking results.
The laser beam is projected through two beam deflecting mirrors mounted on high-speed, high-precision galvanometers. As the mirrors rotate under the direction of the system computer, the laser beam scans through the marking surface of the target to “draw” the desired marking image.
Once the laser beam is deflected from the beam’s steering mirrors, it is focused to the smallest possible spot using flat-field focusing optics. The Flat Field Focusing Assembly is a multi-element optical device designed to keep the focal plane of the laser beam focused in 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 on a small spot and scan the laser beam on the target surface with high speed and precision. With the CO2 laser setting, the diameter of the focused spot and the associated marking line width is approximately 0.0035 “to 0.004”. Human-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 point of 0.004”.
PCB marking
To mark printed circuit boards, the heat generated by the laser beam thermally alters the surface of the board to create a legible and contrasting mark. The process does not require labels, stencils, perforations or any other auxiliary or consumable hardware.
For printed circuit board applications, several different variations of this technique can be used for different board / cladding materials and background conditions.
Solder mask or other coatings formed on FR4 plates –
The laser beam can alter the texture of the coating, giving it a lighter contrast appearance, or it can completely remove the coating to expose the underlying substrate or copper ground plane.
FR4 uncoated –
The laser beam alters the surface texture of the FR4 producing an almost white appearance.
Screen-printed ink block –
For users who already have screen-printed component identification or other fixed information on their boards, a block of white screen-printed ink can serve as the background for the 2D matrix code to optimize readability. This technique is particularly useful when …
o The background color of the board is similar to the color of the laser mark.
o The underlying circuitry would hide the brand image from code readers.
o The plate material is not suitable for laser marking, such as ceramic substrates.
2D matrix code verification
Verifying the readability and content of the 2D matrix codes is an important step in the overall quality program. After marking 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 to be marked.
The reader also assesses the readability of the code based on a variety of parameters including foreground / background contrast, geometric accuracy (skew, quadrature, etc.), and the dimensional accuracy of marked and unmarked cells. Codes in the 2D matrix are categorized as Pass (Green), Warn (Yellow), or Fail (Red). For overall production efficiency, the laser system can be programmed to verify only a few selected 2D codes on a panel, then to automatically switch to verifying each code if the readability of the code falls below a specific 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 after the laser marker, the verification reader can be configured to evaluate codes based on the performance of older subsequent readers to ensure consistent performance throughout the assembly process.
Marking performance
The typical PCB marker is a fully automated and SMEMA compliant conveyor belt laser marking system. The overall productivity of the laser marker is made up of several steps that make up the marking cycle. The steps required to mark a multi-matrix panel are …
1. Transport and positioning of the panel in the marking area.
2. Fiducial location detection (optional)
3. Marking the first circuit of the matrix
4. Checking the marked 2D matrix code (optional)
5. Movement of the laser marking head to the next circuit of the die.
6. Repeat steps 3 and 4 for the remaining circuits in the matrix.
7. Transport of the panel outside the laser marking system (synonymous with bringing the next panel)
Cost of operation
The cost of operation is much less than $ 1.00 per hour. Typical utility requirements are 110 VAC, single phase, 12 A. A compressed air source is required for pneumatics. Total utility costs at maximum laser power (the laser should actually operate at less than 80% of rated power) is $ 0.12 per hour. The main consumable item is the CO2 laser tube that needs to be replaced every 3 to 5 years at a cost typically between $ 1,000.00 and $ 1,500.00. Assuming a 40-hour workweek and 3-year tube life, the tube replacement cost would equal $ 0.18 per hour for a total operating cost of $ 0.30 per hour under worst 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 of marking is less than $ 0.0003 per circuit.
Resume
The electronics industry has been searching for a cost-effective and technically effective means of applying machine-readable codes to printed circuit boards since the 1980s. Early attempts included laser marking of linear barcodes on the edge of the board. A daunting challenge for linear barcode reader alignment and marking alongside circuit traces, also a challenge for barcode readers. The barcode content was limited to a few characters due to limited space and the character-per-inch capacity of barcodes.
The development of 2D matrix code combined with the resolution, permanence and speed of beam-directed laser marking technology now offers manufacturers a reliable, cost-effective, flexible and verifiable means to uniquely identify each product throughout production. , distribution and after-sales.