TO220 heat sink plus to220 MOSFET (with answer) - Page 1
Forum section: electronics / general

author: ahbushnell
author_rank: Frequent Contributor
timestamp: November 27, 2019, 02:36:59 am
content: Hi,I want to make a foot print for a to220 and a heat sink that is board mounted. The Heatsink has a pin for connection to the heatsink. I want to make two foot prints one for each part. I set them up so they have the same origin so they line up when I place them.After I do that I get an error from over lapping foot prints. Can I do something with rules to stop this?ThanksAndyI figured out what was going on. It had nothing to do with interference between the mosfet and heat sink. It was the height limit rule. The MOSFET and the heatsink were busting through the ceiling.

author: Batang
author_rank: Regular Contributor
timestamp: November 27, 2019, 04:09:11 am
content: If you are going to make 2 footprints i.e. TO220 & Heat sinkWhy not make 2 parts, 1 TO220 without heat sink and 1 with.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 27, 2019, 05:59:53 am
content: I do exactly that. Use the stock TO-220 library part (i.e., from my libraries), then make the heatsink with its origin in the same location as the TO-220's origin. Place them in the same location, and there you go.Did you not provide 3D models? If no, Altium assumes the footprint bounding box is collision. If you CBA to add geometry, then you can always add a rule excepting them from collision.Tim

author: ahbushnell
author_rank: Frequent Contributor
timestamp: November 27, 2019, 11:49:32 am
content: I did use a 3D part. The bounding box is rectangular but the heat sink is U shaped.How do I do the rule to avoid collision? I was looking through the rules and I wasn't sure which one. Do I need to make a rule for each pair of parts?ThanksAndy

author: ahbushnell
author_rank: Frequent Contributor
timestamp: November 27, 2019, 11:50:24 am
content: Quote from: Batang on November 27, 2019, 04:09:11 amI did that. But I'm not sure how to deal with the collision.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 27, 2019, 08:34:18 pm
content: ahh. Well, obviously, avoid any intersection or approach within whatever the rule is. Default 10 mils? Can always bump the heatsink back as much, and just ignore the misalignment with pins. Hardware, probably better not to draw it..?Add an exception like so:Component Clearance, add rule, first objectHasFootprint('MyHeatsink')second objectHasFootprint('MyTO220')Or name them by designator, or...Set clearance to 0, or a little negative or something. Set priority so this new rule is done first (should already be there).Alternately, set the global rule to the negation of these, so they are literally never checked. Awkward for many exceptions, though.Tim

author: floobydust
author_rank: Super Contributor
timestamp: November 27, 2019, 09:32:57 pm
content: Altium appears to wrongly use the perceived (silkscreen) perimeter and collisions are a huge PITA with U-shaped or round parts, it assumes the biggest possible square. Seems to be the same Autotrax algorithm from many years ago lives on.Don't forget keepout areas. I don't recommend running traces under a heatsink, where you rely on only the soldermask for insulation. If the aluminum sits flush, it will likely have sharp edges which can cut through.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: December 04, 2019, 03:28:50 pm
content: Quote from: ahbushnell on November 27, 2019, 02:36:59 amI figured out what was going on. It had nothing to do with interference between the mosfet and heat sink. It was the height limit rule. The MOSFET and the heatsink were busting through the ceiling.

author: Pitrsek
author_rank: Regular Contributor
timestamp: December 20, 2019, 08:03:44 am
content: Quote from: Batang on November 27, 2019, 04:09:11 amBecause this would mess-up your BOM. If you have two individual parts, you have two BOM entries with two coordinates(imagine SMD footprint with SMD heatsink - PnP assembly). Also you can mix and match different transistors with different heat sinks. Having individual parts is much more robust approach.

author: Batang
author_rank: Regular Contributor
timestamp: December 20, 2019, 10:44:54 am
content: I was talking about footprints not schematic symbols.Having different footprints for the same part does not mess up the BOM.If you want a TO-220 part mounted horizontal or vertical for example, 2 footprints.