Attempts to cut a solder paste stencil - Part 2

May 12, 2021

More attempts at cutting a solder paste stencil with a rotary engraver.

The 60 degree carbide engraving bit has no problem cutting through 5 thou (0.005") thick stainless. Not only will it cut though, it will completely eat the stainless if the depth is not accurately set.

SS Stencil Cut too deep

This was the first (failed) attempt..

Adding a touch plate

A "touch plate" was added to detect the point at which the tip of the blade hit the surface of the material. In my case the touch plate is just a 50 thou thick copper clad board.

Touch plate

When the command is sent, the firmware starts tracking down slowly until the tip it hits the touch plate. The plate is pulled up with a pull up resistor and touching shorts to ground.

It then records the step count to that position and adds an offset for the thickness of the touch plate. Another command sets this as a virtual Z-zero position so in the G-Code can use Z0 as the top of the material.

Material pull up

Another problem I'm facing is material pull up. If the depth is set just enough to punch through, the cutter can lift up the stainless sheet and completely destroy it...

SS Stencil pull up

A fixture that keeps the sheet under tension should fix this. Also flipping the roll so the natural curve is set to push down towards the backing helps.

Not cutting through

If it's not deep enough, the cutter just indents the stainless and doesn't cut through.

However, despite going past the board and into the backing material it still doesn't cut through!

SS Stencil not cutting through

In this picture the backing material was also not flat.

Using multiple cuts

Cutting several times at the same depth cleans up the edges, but it does not solve the cutting through.

SS Stencil multiple cut passes

More to come

Still more things to try. I have a 30 degree bit on the way and may try cutting from both sides.

The QFN pads are not within the safe pad area to wall area ratio so even if I can figure out a way to cut through cleanly I'm not sure if the solder paste will properly release.

I don't know if anyone reads this, if you find it interesting or have any tips, please send me a message.

Have a great day!