Marking 2D Codes on Printed Circuit Boards

One of the finishing steps in the PCB fabrication process is to apply a solder mask to seal out contaminants. Solder mask, a clear epoxy, can be dyed various colors with green being the most common circuit board color. With the adoption of the RoHS Directive (Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment), some manufacturers have opted to color-code boards so that it is immediately obvious which boards are compliant and which are not.

This particular application test demonstrates the results of marking both blue and red Liquid Photo-Imageable (LPI) solder masks. LPI solder mask is widely used on circuit boards as it offers high resolution, excellent electrical properties, and compatibility with surface mount technology. Synrad CO2 lasers and FH Series marking heads can easily mark LPI solder mask without exposing the electrical traces, or otherwise damaging the board. The 10.6-micron wavelength discolors the dyed surface, which produces a highly contrasting mark. 

For these samples, our marking setup consisted of an FH Series Index head, a 48 Series 10 W sealed CO2 laser, and a copy of our WinMark Pro laser marking software. We created a twelve-character Data Matrix 2D code and human-readable text object in the Drawing Editor. The Data Matrix code, measuring 4 mm (0.16”) square, was created with the 2D Barcode Bitmap property set to No and the 2D Barcode Circle Radius property set to 40%.

We marked PCBs coated with blue and red solder mask using the same parameters—10 watts of
power at a speed of 12.5 inches per second in
an overall cycle time of 0.40 seconds per part.

This double layer LDPE film was cut using
150 watts of power at a rate of 150 feet per
minute (1800 inches/minute). Air assist at
125 PSI was used to separate the layers and
prevent bonding during the cut process.

Degating Cell Phone Components

The traditional injection molding process creates parts where a gate or sprue is still attached to one or more pieces in each shot. Because the sprue is removed before assembly, it is typically removed at or near the injection mold so that the plastic material can be reground, remelted, and reused. Although hand trimming by workers using sharp razor knifes is commonplace, the production volume and complexity of today’s consumer products dictates a faster, more precise trimming solution. To support high-throughput speeds, the best solution is the installation of a Firestar sealed CO2 laser from SYNRAD. Beam delivery to the part surface is accomplished through fixed or flying optics, by moving the laser, by moving the part, or by galvanometer beam steering. The result is a perfect cut every time on every part.

The polycarbonate sprue inside the cell phone
case (above left) was precisely cut at three
different points in a cycle time of only 0.3 seconds
per part. The finished piece is shown on the right.

The accompanying photograph shows before and after views of a polycarbonate cell phone case where the task was to trim the sprue from each part at three different attachment points. Our setup consisted of a Firestar 100 watt laser connected to an FH Series marking head and 125 mm high-power optic that provides a 180-micron (0.007”) focused spot with a 3-mm (0.118”) depth of focus. The maximum width of each sprue attachment point was 5.1 mm (0.2”), so we created a mark file with three lines measuring 5.1 mm (0.20”) in length and used WinMark Pro’s precise positioning capabilities to place each line accurately within 0.0025 mm (0.0001”). To cut through the 1-mm thick (0.04”) polycarbonate case, we set a Power (duty cycle percentage) corresponding to 100 watts and set a cutting Velocity of 50.8 mm per second (2 inches/sec). Using these parameters, we successfully trimmed each case in a cycle time of only 0.3 seconds per part. The cut edge is clean with no residue and a very slight amount of melt back.