Circuit boards, as well as most other components in the manufacturing supply-chain, are bar coded to allow tracking throughout the process from raw board creation to final assembly. Bar coding solutions include affixing pre-printed labels, ink-jet printing, or laser marking. In laser marking applications, marks are typically made on a laser-markable label or ink patch to prevent damage to the FR4 substrate because direct marking frequently results in pinholes through to the underlying copper layer.

The Synrad Applications Lab has developed a set of marking parameters that enable direct 2D coding of FR4 without introducing pinholes into the copper layer. To accomplish this task, we set up an FH Series marking head with a 125 mm lens (180 micron spot size with a 3 mm depth of focus) and then developed a mark file using WinMark Pro laser marking software. In WinMark, we created a 14-character 2D Data Matrix code and set Velocity to 35”/second, Power to 6 watts (duty cycle percentage depends on the laser used), and Resolution to 500.

On the Format tab, we set the 2D Barcode Bitmap property to No (so that we mark unfilled vector circles instead of raster-filled squares) and reduced 2D Barcode Circle Radius to 50%. The resulting code marked in a cycle time of 0.26 seconds and features a cell size of just over six mils (0.00625”) with an overall code size of 0.1” square. We verified code readability using an RVSI CM4000 vision system.