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tony902
United Kingdom
1 Posts |
 Posted - 23 Nov 2016 : 11:20:02
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I need to create a footprint for a Texas Instruments VSON10 package (for an LM5165 regulator). This is a complex shape as, in addition to the pads for pins, it has a large thermal relief pad under the chip and this has four fingers (like short tracks) extending from it. It also has five plated through holes in the thermal relief pad which need to find their way to a ground plane on the board underside. Finally the paste stencil divides the paste applied to the thermal pad into four rectangles so that it does not give 100% coverage on the thermal pad.
What is the best way to create this package? I've done the pins and created the thermal pad outline as a Shape on Layer 1 Top Elec. I need to add the plated through holes - should these be "Pads"? When I place one of these, it gives it a pin number and name, which I don't want. And how do I create the paste shape? The PCB footprint editor has a layer bar on the right-hand side, which offers layers Top Silk, Top Assembly and Top Elec only, there isn't a Top Paste layer and I can't see how to add one.
Thanks! |
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edrees
United Kingdom
779 Posts |
Posted - 23 Nov 2016 : 11:43:36
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The example layout on Page 37 of the TI LM5165 data sheet illustrates a much simpler arrangement than you describe. Large areas of the solder paste stencil will probably be automatically divided into smaller rectangles by the stencil manufacturer.
You can connect multiple vias to the same net in the Component editor, so additional pin names/numbers are not a problem.
Add special layers to add paste/resist layers in the Design Tech file. You can them edit these items freely. |
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Iain Wilkie
United Kingdom
1016 Posts |
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neilh
USA
23 Posts |
Posted - 19 Apr 2017 : 16:02:03
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I'm attempting to use this type of PCB symbol as well.
The SON/QFN packages by TI are over 10yrs old, and some components TI is only specifying this footprint.
It would be really nice to have an EasyPc tutorial on how to use the latest EasyPc v20 to create this footprint for PCB that can also be used to create the Paste Stencil.
(I use www.oshstencils.com and I have used the mylar versions, but for QFN 0.5mm I'm switching to the stainless in the future )
Creating a reliable workable Paste Stencil for the component is essential for these components.
I had this pointers from support,
www.numberone.com/faq.aspx?KB020033
www.numberone.com/faq.aspx?KB020093
www.numberone.com/faq.aspx?KB020099
And following them for creating a VQFN 24 pcb symbol for a TI bq24296.
I ended up calling the symbol "QFN24bullet_480mm_38pins"
to identify it and pull it into a component.
It ended up with 24pins that are real + the underside pad
9pins associated with the vias
4pins associated with exceptions created on the past layer
It seems like there should be a way of combining pins on the PCB symbol, and in
http://www.numberone.com/faq.aspx?KB020093
it says:
"Before finishing with the symbol, you also need to mark each of the electrical (copper) shapes to specify which pad they belong to. This is done using the Pad Number field on the Properties dialog for the shape. If you don't do this, you will find that Design Rule Check flags an error between your pad and the copper because it doesn't know they are supposed to be treated as part of the same item."
However this property with EasyPc20.4 doesn't appear for me.
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Iain Wilkie
United Kingdom
1016 Posts |
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Topic |
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Best approach to create complex PCB footprint