Three notches on TO-126 package - Page 1
Forum section: electronics / beginners

author: tchicago
author_rank: Regular Contributor
timestamp: June 24, 2022, 07:40:36 pm
content: Most of the devices in TO-126 package have three notches around the hole. What are they for?The generic package specifications for TO-126 don't mention those notches.

author: Gyro
author_rank: Super Contributor
timestamp: June 24, 2022, 07:59:59 pm
content: I've always assumed that they were for mechanical stress relief. I don't remember ever seeing a TO126 without them, and I've never seen any mounting hardware that mechanically mated with them. Just one of those things that have always been there and never seem to have been questioned.

author: wraper
author_rank: Unknown
timestamp: June 24, 2022, 08:02:18 pm
content: Could be for holding leadframe in place during encapsulation.

author: strawberry
author_rank: Super Contributor
timestamp: June 24, 2022, 09:18:23 pm
content: flux capacitors

author: David Hess
author_rank: Super Contributor
timestamp: June 25, 2022, 02:36:22 am
content: Quote from: wraper on June 24, 2022, 08:02:18 pmI have seen the same thing and always assumed it was to hold the leadframe during encapsulation.

author: wizard69
author_rank: Super Contributor
timestamp: June 25, 2022, 06:20:48 am
content: The transistorsare just keeping count of the number of resistors that are now 6 feet under.I actually have no idea but earlier suggestions about the assembly process make a lot of sense to me.Quote from: tchicago on June 24, 2022, 07:40:36 pm

author: golden_labels
author_rank: Super Contributor
timestamp: June 25, 2022, 07:38:10 am
content: Tangential: I wonder how many people have placed some features in their designs only to make users wonder what they’re for.So far this thread is already the top result for “to-126 notches”. Congratulations: it seems not many people asked that question before.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 25, 2022, 08:16:12 am
content: Obvious. They're Mitsubishi.Seriously though, I'd guess clamping leadframe as well.At a glance, most of mine don't have this feature (N ~ 4?), but an NEC made part does (N = 1). Hardly a representative sample size, of course.Tim

author: David Hess
author_rank: Super Contributor
timestamp: June 25, 2022, 05:33:56 pm
content: The larger TO-127 package has them also.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: June 26, 2022, 11:50:03 am
content: Some of the early american made ones had notches on the top edge.No idea why either.Jeff

author: David Hess
author_rank: Super Contributor
timestamp: June 27, 2022, 02:50:19 am
content: The modern TO-247 has a notch on each side which exposes the leadframe.I think the leadframe explanation is the correct one. Packages like the TO-220, which have an exposed leadframe, sometimes have notches and sometimes do not, but all of the packages with a hidden leadframe seem to have notches exposing it.Modern packages, and the TO-126 (TO-225) and TO-127, have the advantage over the TO-220 of not requiring insulating hardware for the screw attachment, but without an exposed leadframe, some means must be made available to fix the leadframe in place during encapsulation.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 27, 2022, 04:42:24 am
content: The scallops I believe are a definite feature of the TO-220AB variant. As well as a thicker tab, no round pins, and other weirdnesses the very old drawing (plain vanilla TO-220) has.TO-3P doesn't have any I can think of seeing, but it does have a fair amount of tab exposed, which, maybe that does as well of a job.Tim