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| From: | "Peter Clifton (petercjclifton AT googlemail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com> |
| Date: | Wed, 18 Jan 2017 12:21:31 +0000 |
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| Subject: | Re: [geda-user] QFN packages solder mask |
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--001a114fe724f643d605465d74ca Content-Type: text/plain; charset=UTF-8 On 18 Jan 2017 12:06, "John Luciani (jluciani AT gmail DOT com) [via geda-user AT delorie DOT com]" <geda-user AT delorie DOT com> wrote: What type of stencil openings are you using? For the thermal pads I typical reduce the coverage to between 50 - 70% (depending on the aperature dimensions). The reduction is done using a layout similar to your footprint. The spacing between the paste areas provides the channels. I also reduce the coverage on the electrical pads. John L Presumably this means you take full control of the manufacturing process? Many fab houses I've encountered often seem to want 1:1 mask to copper pad (and I "think", stencil). This isn't so they manufacture like that, just so it is easier for them to apply their own process corrections. (Like we specify plated hole size, not drill size). Does your safety critical line of work mean you need to capture the complete production tooling at design stage, or is this just a good practice or personal preference? In mechanical stuff, I've had similar with sheet metal fabricators. Some prefer you model folds at a nominal bend radius, then apply their own material allowance corrections. (Easier than if the customer models something arbitrary and wrong). With our current guys, I have a copy of their correction factors - so I model it that way in the MCAD, and my model matches what their tooling will fold. Means they can make what I want with only minimal, or no correction to the flat pattern drawings I send along with the 3D models. Peter --001a114fe724f643d605465d74ca Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable <div dir=3D"auto"><div><br><div class=3D"gmail_extra"><br><div class=3D"gma= il_quote">On 18 Jan 2017 12:06, "John Luciani (<a href=3D"mailto:jluci= ani AT gmail DOT com">jluciani AT gmail DOT com</a>) [via <a href=3D"mailto:geda-user AT del= orie.com">geda-user AT delorie DOT com</a>]" <<a href=3D"mailto:geda-user@= delorie.com">geda-user AT delorie DOT com</a>> wrote:<br type=3D"attribution"><= blockquote class=3D"quote" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc = solid;padding-left:1ex"><div dir=3D"ltr"><div><div><div><div><div><div>What= type of stencil openings are you using?<br><br></div>For the thermal pads = I typical reduce the coverage to<br></div>between 50 - 70% (depending on th= e aperature dimensions).<br></div>The reduction is done using a layout simi= lar to your footprint.<br></div><div>The spacing between the paste areas pr= ovides the channels.<br></div><div><br></div>I also reduce the coverage on = the electrical pads. <br><br></div>John L</div></div></blockquote></div></d= iv></div><div dir=3D"auto"><br></div><div dir=3D"auto">Presumably this mean= s you take full control of the manufacturing process?</div><div dir=3D"auto= "><br></div><div dir=3D"auto">Many fab houses I've encountered often se= em to want 1:1 mask to copper pad (and I "think", stencil). This = isn't so they manufacture like that, just so it is easier for them to a= pply their own process corrections. (Like we specify plated hole size, not = drill size).</div><div dir=3D"auto"><br></div><div dir=3D"auto">Does your s= afety critical line of work mean you need to capture the complete productio= n tooling at design stage, or is this just a good practice or personal pref= erence?</div><div dir=3D"auto"><br></div><div dir=3D"auto">In mechanical st= uff, I've had similar with sheet metal fabricators. Some prefer you mod= el folds at a nominal bend radius, then apply their own material allowance = corrections. (Easier than if the customer models something arbitrary and wr= ong).</div><div dir=3D"auto"><br></div><div dir=3D"auto">With our current g= uys, I have a copy of their correction factors - so I model it that way in = the MCAD, and my model matches what their tooling will fold. Means they can= make what I want with only minimal, or no correction to the flat pattern d= rawings I send along with the 3D models.</div><div dir=3D"auto"><br></div><= div dir=3D"auto">Peter</div><div dir=3D"auto"><br></div><div dir=3D"auto"><= br></div><div dir=3D"auto"><br></div><div dir=3D"auto"></div></div> --001a114fe724f643d605465d74ca--
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