Anyone Have Experience With SOT89

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I am curious why all recommended footprints for SOT89 seem to allow the pins to overhang on the inside.  I fear this could cause shorts.   
Here is a Valor VPL review of the standard SOT89 footprint. Has anyone else experienced this?   
I've also attached a datasheet - uploads/107/Case_style_Dimension_DF782.pdf

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rickdehart Members Profile Send Private Message Find Members Posts Add to Buddy List Advanced User Joined: 18 Apr 2012 Location: Austin, TX Status: Offline Points: 184	Post Options Post Reply Quote rickdehart Report Post Thanks(0) Quote Reply Topic: Anyone Have Experience With SOT89 Posted: 12 Jul 2013 at 3:51pm
	I am curious why all recommended footprints for SOT89 seem to allow the pins to overhang on the inside. I fear this could cause shorts. Here is a Valor VPL review of the standard SOT89 footprint. Has anyone else experienced this? I've also attached a datasheet - uploads/107/Case_style_Dimension_DF782.pdf



Tom H Members Profile Send Private Message Find Members Posts Add to Buddy List Admin Group Joined: 05 Jan 2012 Location: San Diego, CA Status: Offline Points: 5716	Post Options Post Reply Quote Tom H Report Post Thanks(0) Quote Reply Posted: 12 Jul 2013 at 6:01pm
	The SOT89 was one of the first SMT components invented. There is no real industry standard so every mfr. makes their own version. For the Footprint creation I normally add 0.05 mm (2 mils) periphery around the component lead. I don't understand the datasheet link you provided where the component lead is Q = 0.062" but the mfr. recommended pattern has the pad length 0.059" which is smaller than the lead. So I don't trust the datasheet. The VPL only matches a specific mfr. part number with a footprint and there are dozens of different part numbers. You are correct that the footprint in your picture with the VPL lead will short to the copper pour. We have avoided creating a SOT89 component family for the Library Expert because pin 2 is irregular shaped and comes with many variations. This is one of those parts that you create once and never create it again (hopefully).
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