Laser Marking of QR and Data Matrix Codes
by Scott Sabreen
The drive to encode more information, in combination with smaller space requirements, led to the development of 2D "Data Matrix" and "QR" Codes. These codes provide quick access to the internet, corporate branding or other information and must be scanned by a camera capture device.
Both QR and Data Matrix codes are markable using traditional near-infrared (1064nm wavelength) industrial lasers, including Nd:YAG, Vanadate and Fiber. The continuous wave (CW) CO2 lasers operate at a wavelength of 10.6 μm (far infrared spectrum) and generate a much lower peak power, yielding colorless engraving (embossing). Thus, they cannot produce high-contrast markings on plastics. Note: CO2 lasers commonly are used for marking barcodes and matrix codes on labels, paper-stock and ink ablation. In certain applications, large size Data Matrix codes marked using CO2 lasers have been achieved.
For plastic products, laser marking is the preferred method because the process yields high-contrast indelible markings and does not require expensive consumable ink/solvents or post-curing. The mechanism of laser marking is to irradiate the polymer with a localized high-energy radiation source (laser). The radiant energy then is absorbed by the material and converted to thermal energy. The thermal energy induces reactions to occur in the material, i.e., the QR or Data Matrix code. Lasers can mark the smallest size machine vision codes. This is important for micro-marking and when there is limited surface area on a part or component to be marked with alphanumerics, logos or schematic diagrams.
Modern machine-vision systems are not just stand-alone inspection devices. Rather, they are integrated into Six Sigma total manufacturing operations, including statistical quality control metrics programs. Industrial manufacturing requirements for indelible direct part marking containing machine vision codes are growing exponentially. Direct part marking enables tracking a product from the time of manufacturing until the end of its useful life. This demand is driven by the increasing requirements for component traceability and product unique identification (UID). Post 9/11, manufacturers are implementing strategies to establish traceability and thwart product tampering and counterfeiting.
Which Code to Use?
The choice as to which code to use is application- and end-use-specific. A few general guidelines include the following:
- Small, tight laser-marked surface areas containing small encoded alphanumerics are required (ECC200).
- Data Matrix will generally laser mark faster than QR codes; however, speed is somewhat dependent on the software and knowledge of marking machine vision codes, including lighting set-up. Cell module sizes as small as 0.004" and less are achievable.
- Encoding images and logos
- Relatively large product surface areas are available.
- Esthetics of the code are important – often QR codes appear more visually appealing.
- QR codes have several modes of encoding data, some of which can be more compact than the 8-bits per character used by Data Matrix.