In Knol-edge, Harrie Knol shares his knowledge on precision metal. Harrie is Head of Application Engineering at Veco and helps our clients' engineers to shape their projects.
In this video Harrie talks about Stencil Printing vs. Screen Printing.
Today we are going to talk about stencil printing vs. screen printing. These both printing technologies are the way to print a solid paste on PCBs, to paste solid paste on components, print components themselves or print silver lines on solar cells. Until now it has been the conventional way to do it, is by screen printing. It's a screen in combination with an emulsion. And all the people in the field of conventional screen printing are looking for a screen with the highest open area. In fact, if you think what they're looking for, in fact they say they don't like the screens, so they don't like the screen at all. And that has been the reason for us, for Veco to develop a stencil.
To get back to this conventional screen printing, as I said it's made by a wire mesh in combination with an emulsion. It's not weather resistant and due to the wire you get knots in your printing result. That means that you have to make several prints to avoid these knots and also because the wires can move, the product is not stable. And therefore we switched to stencil printing.
Stencil printing, in fact, is the same as screen printing but we replace emulsion by a full metal and we don't use a screen at all. Because it's full metal, there’s no wear of the stencil. We can use them 15,000, 20,000, 30,000 times, whatever you want. As long as there is no human failure and the wafers don't break, the stencils will not wear.
We can print very high aspect ratios. Aspect ratios with conventional woven wire are about 0.5. We can achieve 25 micron white lines in 35 micron thickness. That means your expected ratio is higher than one. And that also means that we can do a single print. Very important because that also means that even if you want to raise your output, you can use our stencils in the same equipment as you're currently using.
And last but not least, on solar cells we have proven a 0.3% yield on the efficiency of the solar cell. So normally, these yields are about 21%-22% and we can raise them with 0.3% extra on top of this 22%.
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