when the (expletive) did TO-220 tabs get so thin? - Page 1
Forum section: electronics / projects

author: RJFreeman
author_rank: Regular Contributor
timestamp: July 30, 2015, 12:29:21 pm
content: So I was assembling a power supply and I noticed that the tab (where the screw goes through) on the 7812 I had ordered from Digikey was awfully thin, roughly 0.5mm, so much so that the insulating bush was stopping the screw from holding the TO-220 down firmly, likewise an LM317 I had purchased from Digikey was the same.My first thought was that I had some dodgy counterfeits, but I would have not expected that from Digikey (although maybe I am being naive) as both were marked as being made by On Semiconductor I figured I would double check what I had ordered ( LM317TGOS-ND and NCP7812TGOS-ND ) on checking the Datasheets for these devices from On Semiconductor;http://www.onsemi.com/pub_link/Collateral/LM317-D.PDFhttp://www.onsemi.com/pub_link/Collateral/NCP7800-D.PDFSure enough on the last page of these datasheets, 'Dimension S' for the LM317 is specified as 0.506mm to 0.61mm while for the NCP7812 this can be anywhere between 0.506mm and 1.39mm?Most other TO-220 package specifications (form other manufacturers) give a range of 1.1mm to 1.4mm, roughly twice what these devices have - so when did this change?Is this a specific variation of the TO-220 - if so which variation?Is it only On Semiconductor doing this?How the heck are you supposed to allow for a 1:2.7 range?And are there thinner mounting bushes available?

author: wraper
author_rank: Unknown
timestamp: July 30, 2015, 12:34:32 pm
content: Check this datasheet from ST (single/dual gauge TO-220):http://www.mouser.com/ds/2/389/CD00000444-249828.pdf

author: RJFreeman
author_rank: Regular Contributor
timestamp: July 30, 2015, 12:39:46 pm
content: Quote from: wraper on July 30, 2015, 12:34:32 pmYep, ok, I see ST are 0.51mm to 0.6mm as well.must have been going on for a while then if the contagion has spread, and maybe this is just the first time I have seen it?

author: RJFreeman
author_rank: Regular Contributor
timestamp: July 30, 2015, 12:43:14 pm
content: Ah, actually, on reading further, now I see the point you are making Wraper, there is a 'single gauge' and a dual Gauge' version, and presumably in the case of the NCP7812 from On Semiconductor a 'whatever the heck we feel like at the time' version....

author: MagicSmoker
author_rank: Super Contributor
timestamp: July 30, 2015, 12:44:52 pm
content: Quote from: RJFreeman on July 30, 2015, 12:29:21 pmMy guess is that this is the result both of ruthless cost-cutting, but also the increasing popularity of using spring clips that either press on the plastic package or the tab to attach the device to a heatsink. The spring clips automatically take up differences in tab/package thickness, are much less labor-intensive to install and eliminate the possibility of warping the tab from excessively torquing the mounting screw (or equally as bad: not tightening the screw enough so that the device overheats and the screw and/or nut eventually comes off and rolls around inside the enclosure randomly shorting crap out).

author: tszaboo
author_rank: Super Contributor
timestamp: July 30, 2015, 12:47:33 pm
content: Somewhere around 2006. week 31.http://www.onsemi.com/pub/docs/pcn/15550.pdf

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 30, 2015, 01:29:27 pm
content: In fact, the ancient JEDEC standard allows thin tabs, so it's always been there as an option, it's just rarely used -- for whatever reason!Fortunately, 78xx don't matter, because you can't use more than 10W or so anyway. If you need more, you need a bigger regulator anyway; or even better, consider a switcher.I've seen round lead TO-220s, too.TO-220AB is a tighter spec standard (and has those adorable dimples), if you're looking to be selective.Tim

author: technix
author_rank: Super Contributor
timestamp: July 30, 2015, 01:32:54 pm
content: Hmm... I got all my parts from Taobao (domestic version of Aliexpress) so... Here are my measurements of thickness of tabs of 24 TO-220 packages from 7 parts and a different batch of one part, 3 randomly selected from each batch: Every measurement is taken with the caliper at the bottom of the tab, with the pins of the part facing down.Voltage regulators:LM317TCCOXC W MAR 1428 (STMicroelectronics): 1.32mm, 1.31mm, 1.31mmNIKOL1117T-3.3DB3512928A: 1.31mm, 1.31mm, 1.33mmAZ1117T-5.0E1 603J61: 1.34mm, 1.34mm, 1.34mmL7805CVCCOKJ V6 MAR 1315 (STMicroelectronics): 1.06mm, 1.06mm, 1.06mmL7805CVCCOKJ V6 MAR 1412 (STMicroelectronics): 1.05mm, 1.05mm, 1.05mmTRIACs:345C226TIC206MPHILIPPINES: 1.29mm, 1.30mm, 1.29mmPower transistors:B08TIP32C(Fairchild): 1.37mm, 1.40mm, 1.37mmIRF4905IR 803P CJ LU: 1.35mm, 1.36mm, 1.34mmSo among those only 7805 got the thin 1mm tab, and everything else is rocking a 1.3mm one... What the hell, STMicroelectronics?!

author: SeanB
author_rank: Super Contributor
timestamp: July 30, 2015, 05:57:51 pm
content: Cost of the copper in the alloy. If you halve the cost of the package ( biggest cost is that copper tab, the epoxy cost is almost nil) and multiply thast by a 100 million devices a year you save a pretty penny. Useful for those applications where they solder the device to the board in any case, and run it at a low thermal load, or use spring clips on the package ( or a bar across a whole load of devices on a common heatsink) where cost is the primary spec.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: July 31, 2015, 12:59:05 am
content: TO-3s also have variations , about 2:1. My PMC 2N3055 has about 3mm thick base, but my ST LM323K only looks about 1.5mm.

author: Pjotr
author_rank: Frequent Contributor
timestamp: July 31, 2015, 08:33:39 am
content: Quote from: Alex Eisenhut on July 31, 2015, 12:59:05 amThat is the case as long as 2N33055 are made. Depends on the material of the case. Some came in an aluminium case (i.e. Motorola) that is softer and had a 3 mm base. Others came in a stiffer steel case (i.e. TI) with a 1 - 1.5 mm base.

author: SeanB
author_rank: Super Contributor
timestamp: July 31, 2015, 04:56:22 pm
content: Telefunken did also make some TO3 in a Kovar case, they were sometimes used in old TV sets to house a line output transistor. I know IBM also did some in a fully gold plated case, along with SGS Thompson for some of the military/Aerospace qualified devices. Still have some gold plated TO66 packages around somewhere.

author: wraper
author_rank: Unknown
timestamp: July 31, 2015, 05:16:57 pm
content: Quote from: technix on July 30, 2015, 01:32:54 pmI guess that they are just counterfeits. Because they are nor single, nor dual gauge TO-220 (no such thickness in ST datasheet).

author: marshallh
author_rank: Unknown
timestamp: July 31, 2015, 06:02:07 pm
content: There have been problems in the past with ST ldos and counterfeits.

author: technix
author_rank: Super Contributor
timestamp: August 01, 2015, 04:33:59 am
content: Quote from: wraper on July 31, 2015, 05:16:57 pmSo as it turns out that those 7805's that I don't use are counterfeits, but the dubiously-branded 1117's I'm using a lot are more likely to be genuine...

author: Simon
author_rank: Unknown
timestamp: August 01, 2015, 10:53:02 am
content: This would be like the one Dave found in a rigol power supply and was overheating. The problem is that some manufacturers are using them to save cost and trying to screw them to heatsinks. I had a load from Farnell like it. They would make sense in many applications but chances are they will get misused. screw one down to a heatsink and it will just bend and the only thermal contact will be in the small compression area the screw creates.

author: technix
author_rank: Super Contributor
timestamp: August 01, 2015, 01:36:18 pm
content: Quote from: Simon on August 01, 2015, 10:53:02 amMaybe it is going to be a better idea to screw the TO-220 and the heatsink together before soldering them down - so if a thin tab is encountered you can bend the leads to comensate.By the way, manufacturers, if you are going to keep making thin-tab TO-220s please place the leads a bit further to the front - whatever tab thickness you use, just keep the leads-to-heatsink spacing the same.

author: technix
author_rank: Super Contributor
timestamp: August 01, 2015, 01:41:22 pm
content: Quote from: T3sl4co1l on July 30, 2015, 01:29:27 pmThe scary thing is that they could start producing other power electronics, like power MOSFETs, with thin tabs too. Those will be a nightmare. I will never trust putting 100A through a thin-tab TO-220 MOSFET.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 01, 2015, 03:32:05 pm
content: Quote from: technix on August 01, 2015, 01:41:22 pmWell, they wouldn't, because 100A MOSFETs are expected to dissipate quite a lot, and they wouldn't be able to if they weren't made with heavy copper.But on that note...It amazes me that D/2PAK parts are always made with heavy tabs, and ludicrous ratings. 99% of all PCB applications can't make use of a minuscule fraction of their total dissipation capability. It would make sense to save those few cents for such applications!Tim

author: DanielS
author_rank: Frequent Contributor
timestamp: August 02, 2015, 04:17:08 am
content: When I want something that can sink a lot of power, I use TO-3P or TO-247 - nearly all the most promising MOSFETs I have seen for linear power applications around 100W are TO-3P.

author: technix
author_rank: Super Contributor
timestamp: August 03, 2015, 05:01:51 pm
content: Quote from: DanielS on August 02, 2015, 04:17:08 amDuring my experimenting with homemade LDO I pulled a few amps through a IRF4905, which is a thick tab TO-220 part. I am wondering if I should use a TO-247 (or TO-3P) PMOS in the final design...