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Forum Index : Microcontroller and PC projects : What’s with the new TO220 tabs?
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9750 |
Why is it that every new TO220 device I buy these days has the tab only half the thickness that the old ones used to be? 0.5mm to be precise. I don't like them.  The original ones that were about 1.3mm thick, you cold mount and bolt them down hard and know they were set for life then. These newer ones with the thin tab are a pain, cos if you happen to over-tighten them, the tab itself deforms, and the package is moved away from the heatsink making a lovely air-gap so the device can rapidly overheat. This is with the same kind of torque I would have used on the thicker ones. Lower torque gets you around that problem, but then I have the uneasy feeling that they are not secured firmly enough, cos the thin tabs you can only nip them up and no more, or you bend the silly little 0.5mm tab. Tab aside for the moment, the thinner ones also mean that the hundreds of isolation washers I have for TO220 packages are now too thick, and you have to trim about half a mm off the end of them - difficult to do neatly. I suppose I will have to just have to see if I can get thinner insulation washers. Grogster no like.....  Yes, this is a bit of a rant, as I have just had to try to mount some of these bloody things.  Smoke makes things work. When the smoke gets out, it stops! |
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Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5157 |
Gizmo no like either. The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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MicroBlocks Guru  Joined: 12/05/2012 Location: ThailandPosts: 2209 |
heat transfer paste and loctite are your friend. Microblocks. Build with logic. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9750 |
I use paste or those heat-transfer silicone insulator things. Usually the latter, as it is not as messy. I would still love to know WHY the hell they make the tabs so thin as to just about be useless for bolting to anything. The old thicker ones worked beautifully, so why change what is working? Grrrrrrr. Smoke makes things work. When the smoke gets out, it stops! |
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| Boppa Guru Joined: 08/11/2016 Location: AustraliaPosts: 816 |
cause its cheaper???? :-( My biggest worry is that at every mechanical junction there is a thermal inefficiency so that thinner tag is going to, of necessity, run the device hotter at times This is of course bad when things are already being pushed close to the limits |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2463 |
think about it like this: when 1 and 2 cent coins were phased out in new zealand, the scrap metal value of the coins was greater then the face value. now, i'm picking that an old-style TO-220 package would contain a similar amount of copper as a 1 cent coin, hance require in excess of 1 cent worth of copper to make. if you're a factory making components that sell for a few cents each in bulk, and you can trim half a cent of cost off each component by halving the copper content... that amounts to a significant percentage reduction in your per-unit production cost (and a a significant percentage increase in your profit margin). btw: to trim an insulating washer, place the washer through the new-style TO-220 package, then use a single-sided razor blade to cut off the excess plastic sticking out through the hole on the other side. as for deforming the copper tab, in theory you should be using a rectangular steel spreader washer anyway - transistor manufacturers used to not guarantee TO-220 packages that were attached without using a rectangular spreader. cheers, rob :-) |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9750 |
Annoyingly, that makes sense.  Do you know where I might acquire some of those steel spreader washers? Smoke makes things work. When the smoke gets out, it stops! |
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| robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2463 |
i've not seen them for sale for many years now, just did a search on ebay and drew a blank. however, google did find this one webpage: https://www.rfparts.com/rftransistors/insulator-kit-to220-transistors/insulkit.html you could always start off with a regular round washer and file down a flat i guess. but the washers do need to be fairly sturdy so they don't deform when tightened down. cheers, rob :-) |
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| Phil23 Guru Joined: 27/03/2016 Location: AustraliaPosts: 1667 |
Can I add this to my "Blame the Accountants" list? Probably an X% reduction in raw materials, returning a Y% increased dividend to the share holders, an helping the Board secure their place. [/Rant TOO] Cheers. |
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Azure Guru Joined: 09/11/2017 Location: AustraliaPosts: 446 |
There are these screw in clips and these snap on clips to secure TO220 and other types without screwing in the tab. They also often use these silicon boots to insulate them. We use them in fairly harsh environments with rough handling of the equipment and they seem to hold up. Not the best prices in those links, found them as quick links to show what they are like, in case it helps. |
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