Some years ago, the laser-cut stencil has taken over the market for stencils from the etched one. Conical openings, higher precision and faster lead time have been crucial. Not to mention the minor impact on the environment that they contribute. The big disadvantage has always been that it has not been possible to manufacture “multi -level” stencils with laser. Or so-called “step etching”. This may be required when assembly PCB with a large mix of components and where some components require a very small amount of solder paste. It is the size of the opening which, together with the thickness of the stencil, that determines how much solder paste is applied to the solder surface.
For some time now, however, methods have been developed to be able to manufacture “multi-level” stencils with lasers. This is made by laser cutting out the area where the component is located with a sharp cut. In the “hole” that is formed in the stencil, a piece of a thinner stencil (“step-down”) is located and welded to it with an extremely thin spot weld (100 μm) from the underside. It is of course possible to add a thicker part to get more solder paste on a single component (“step-up”). When this is done, the underside is polished and all openings are cut out at the same time as the laser. An after-treatment of the ElectroPolish / NanoCoating type is recommended.
More data can be found on our page about solder paste sheets.
The picure shows the “welding joint”, seen from under side of the stencil.