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Tools of the trade / Re: Cutting mylar stencils with a silohuette cameo
My friend and I have been using a Cameo to make stencils for about 6 months now, and we're really happy with it. We are using some similar parts, so I'll share our experience. Even our best setup doesn't cut the QFN correctly every time, but it's a 1-pass method using cheap material so we usually just cut 2 stencils and see which one comes out best.
We start by using 3mil thick Polyester Film, available in a $15 large roll from McMaster-Carr. We like getting it from here because it's cheap and the properties are tightly controlled (vs transparencies for example, which vary significantly brand-to-brand). That's a little thinner than what you used, and I don't know how the other properties compare, but for us the Polyester cuts well, doesn't crease, and has decent resistance to tearing. McMaster also offers the same material in other thicknesses.
In our experience the 0.5mm pitch TQFP really is about the limit that you can get without doing anything really fancy. We use:
Blade: 2
Speed: 1 (only 1 pass!)
Force: 14 (this varies from 9-21 depending on blade condition, but in general we got best results using the lowest setting that would complete the cut in one pass)
Condition of your cutting mat makes a difference too. Our mat lasted for a couple dozen stencils but at the end we had trouble with the pads ripping out and fouling up the blade. The newer, sticker mat works better.
With the above setup we don't find it necessary to use any fancy tweaks or adjustments. The stencils cut quickly and cleanly because we're only using one pass. The resulting stencils last easily 30-50 uses in one session; overall we've made about 200 boards with this method. On the downside, the 0.5mm QFN only cuts acceptably about 70% of the time, and some poking with a dental pick is usually required to make sure all the pads are actually clear, but the cheap Polyester and quick cut times make some failure acceptable.
Let me know if you have any other questions! We think this method is pretty great as far as DIY goes.
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