Micro 2D code dot matrix marking system and its application

Micro QR code marking is usually done on materials that are sensitive to heat, such as glass and printed circuit boards (PCBs). Dot marking provides the best visual effect because each dot is produced by a single fixed laser beam, which minimizes heat input and achieves the fastest marking speed. This technology is ideal for applications where the code size is approximately 1 to 3 times the focused spot size. For larger codes, the distance between dots will be too large, reducing the readability of the code.

By using WinMark Pro v6 marking software, there is no need to calculate resolution. For demonstration purposes, we are marking a 2D code on an FR4 PCB using a 10 W Synrad CO2 laser and an FH Flyer marking head, both controlled by WinMark Pro v6 software. The marking head is equipped with a 125 mm focal length lens, providing a spot size of 180 um (0.007”).

In WinMark Pro, we create a 3.8 mm × 3.8 mm (0.15” × 0.15”) QR code containing 10 alphanumeric characters. To achieve dot-matrix marking, we first set 2D Barcode Bitmap to No and 2D Barcode Circle Radius to 0% in the Format tab. Then, in the Marking tab, set Spot Marking Style to Yes. After setting the above three parameters, WinMark v6 will automatically ignore Resolution for dot-matrix marking. For PCB marking, Powerproperty is set to 10 W and Spot Mark Duration is set to 5 (0.5 msec), which is the time each dot in the code stays.

Figure 1 Marking a 2D code on a PCB using dot-matrix marking

As a result, the marking time per piece was 170 milliseconds under this setting. The printed QR code is very fine, clear and easy to read, and can be easily read by a handheld code scanner.

How to get the best marking contrast on wood

Generally, in laser marking, the focus of the laser beam must fall on the surface of the material to obtain the best contrast. However, there are some exceptions, such as marking wood materials, where slightly deviating the material from the focus will obtain better contrast. This is because the larger divergent spot reduces the power density of the laser and increases the heating and burning of the material surface, while a small spot with high power density will waste too much energy on vaporizing the wood, which is counterproductive. However, we also need to weigh the pros and cons of this approach. A larger out-of-focus spot will reduce the clarity of the mark and lose some details.

To verify this, we marked the same image on two boards, one with the laser perfectly focused on the board and one with it slightly out of focus to see how the contrast of the two marks differed. The entire marking system consists of an FH Flyer marking head and a 48-2 (25 W) laser, both controlled by WinMark Pro laser marking software. The marking head is equipped with a lens with a focal length of 200mm, which provides a spot size of 290µm (0.011”).

The marking file is an imported .eps vector image of a fire truck and TrueType® font text. We create a 112.5 mm x 139.7 mm (4.43” x 5.5”) boundary in the software, set the power to 25 W, and the marking speed to 254 mm per second (10 in/sec).

Figure 2 The image at the beam focus has fine and clear details but low contrast

Figure 3: The image is taken at 11 mm out of focus. Although some details are lost, the contrast is greatly increased.

The top image is in focus, the bottom image is 11 mm (0.43”) out of focus. The contrast is noticeably increased and the lines are slightly thicker when out of focus. Both took the same 28.89 seconds to mark, and in this case the slightly out of focus mark makes the image more realistic and pops off the board.