Script – Making Solder Paste Stencils
To print solder paste on PCB’s we need a stencil made of stainless steel. This stencil contains cut-outs where we want to have solder paste on the board. With stainless steel stencils we can print multiple boards without losing accuracy.
To define the volume of paste on the board, we can vary the thickness of the stencil. With thicker stencils, more paste is printed. The thickness options depend on the material we have on stock, currently we can cut stencils of 70, 100 or 130 micron thickness.
To cut the stencil, we use a laser cutter from LPKF, the StencilLaser P6060, a relatively small, compact machine with a high cutting speed and a precise enough axial precision of +- 4 micron.
The only supplies it requires for operation are power and air pressure for moving the axes, and oxygen for high quality cutting.
A powerful exhaust is installed to collect and remove the small parts cut out of the stencil.
The stainless steel plate is mounted in a stretching frame with a maximum size of 610 x 850 mm. The maximum working area for cutting is 600 x 600 mm.
We put the stainless steel sheet in the frame, and stretch it with air pressure. The frame with the sheet is loaded to the machine.
The data to cut the stencil are prepared by our CAM team and sent to the machine.
On the machine we have to select a proper template file to define the laser power and the cutting speed for different sizes of pads.
We can use a higher cutting speed for cutting the outlines, because the precision is not as important as for the pads.
When all is configured, the machine measures the dimensions of the sheet and starts the cutting. Depending on the number of pads to be cut, the machine cuts a complete stencil panel in 60 to 90 minutes.
After removing the frame from the machine, we release the air from it, and remove the sheet.
When we have panelised different small stencils, for instance for use with our eC-stencil mate, we push out the individual stencils out of the sheet.
The pads can have small burrs from the burning on the exit side of the laser. With an eccentric vibration grinder we polish the stencils to remove the burrs.
The stencil is now ready to print paste on the boards with our eC-stencil mate manual stencil printer or with our automated printers.