Benefits/application of "precision machined terminal"? - Page 1
Forum section: electronics / beginners

author: fozzyvis
author_rank: Regular Contributor
timestamp: December 16, 2020, 10:20:05 am
content: I've come across these kind of pin headers:https://be.farnell.com/samtec/ts-130-g-a/header-2-54mm-pcb-30way/dp/1668589a number of times and always wondered what benefit they have over "regular pin headers" like these:https://be.farnell.com/samtec/slw-140-01-t-s/connector-rcpt-40pos-1row-2-54mm/dp/2779551.Things I've noticed:They are more expensiveNo springy contacts in the female socketsNot such a wide range of brands have themI can imagine they have the benefit of having tighter tolerances and thus friction fit instead of relying on the springyness of the female headers. Maybe that gives them higher reliability or longer life? Is that it?

author: Gyro
author_rank: Super Contributor
timestamp: December 16, 2020, 11:37:14 am
content: They're really designed for different applications. The cheaper square pin ones are intended for the square hole Samtec female that you linked and similar. The precision machined round ones are intended to fit into turned pin sockets [EDIT: where they areveryreliable] - they're wasted on the standard sockets and will probably have low reliability and retention force as they are smaller diameter.

author: fozzyvis
author_rank: Regular Contributor
timestamp: December 16, 2020, 01:53:00 pm
content: I do understand that they shouldn't be mixed and that using the machined ones in the square sockets is just a bad idea.But what are the advantages or specific use cases of the round ones?

author: Gyro
author_rank: Super Contributor
timestamp: December 16, 2020, 05:42:12 pm
content: I think it's just that turned pin sockets and pins provide a very high integrity. The 4 point internal spring contacts that are stiff enough that they are probably near enough gas tight.Plastic housed single edge square pin contacts, particularly if Tin plated, don't have a particularly low or stable contact resistance. For some precision analogue or High-rel applications this is enough to tip the balance. You get what you pay for.It's just like using turned pin vs cheap side contact IC sockets, sometimes it's worth the extra.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: December 16, 2020, 06:31:19 pm
content: Check the specs on number of insertions, allowed vibration environment, contact resistance and the like. Some applications value this, some don't. And some value the appearance of quality as much as the actual measurable differences.These things change over time, often due to very subtle changes in materials and geometry. When I last really did the data search multiple decades ago the machined pins were superior in the areas mentioned and maybe in others that I don't remember or didn't check. But in the intervening time things like eliminating Beryllium and Lead from items like these may have changed the answers. To definitively answer your question you will have to really understand the properties of the connection system that matter to your application and evaluate the specified performance of the parts against those requirements. That is an almost impossibly tall hurdle for a small or hobby project since defining environments sometimes requires large amounts of testing and analysis. This is one reason why so many systems fail in the field, essentially doing their environmental evaluations at customer expense.

author: dmills
author_rank: Super Contributor
timestamp: December 16, 2020, 10:58:08 pm
content: Got stuffed good and proper a year or so back by connector issues.Cockup involving tin plated header and gold plated socket... In a vibration environment... Yea, don't do that, because it don't bloody work! We wound up field replacing about a hundred units.Expensive sort of mistake, that will not be made again.Regards, Dan.

author: Vovk_Z
author_rank: Super Contributor
timestamp: December 17, 2020, 10:53:32 am
content: I have a small experience that these round precision-machined ones are more reliable with time. I can only guess possibly those round ones have a larger contact area and so gold plating isn't erased as easily as with that sprung square type. So gold plating lasts longer.

author: CaptDon
author_rank: Super Contributor
timestamp: December 17, 2020, 06:03:30 pm
content: At GE locomotive we were using Souriau connectors and in an effortto save money (of course) they went with stamped male pins instead ofmachined pins. One of the pins splayed out upon insertion into the matingconnector on the engine control unit causing two diesel fuel injectors to bemated electrically. Final outcome, 4500hp prime mover blown to bits whenthe connecting rods bent and twisted bringing the pistons down againstthe crankshaft counterweights!!! Over $100k in destruction to save about$100 in pin costs!!! Of course we were forbidden to take pictures of thecarnage!!

author: dmills
author_rank: Super Contributor
timestamp: December 17, 2020, 06:26:45 pm
content: I didn't even know Souriau made stamped pin crap.Certainly everything I have had off them has been at worst respectable, and at best rather nice, but I suppose what GEs bean counters want they get.Regards, Dan.

author: Wendy_Preston
author_rank: Contributor
timestamp: December 18, 2020, 08:28:11 am
content: Quote from: Gyro on December 16, 2020, 05:42:12 pmTypically round pins will be mating with a circular contact clip with 4 points of contact. Square pins mate with stamped female receptacles that are normally just twin beam - two points of contact. With the 4 points of contact, better resistance to vibration and shock is achieved - it's the "secret sauce" behind all our Hi-Rel connectors! They're almost all based on a round male pin and a female clip design with 4-6 contact points. Except for our latest release - Kona (because it's so big) has the male as a split 6-finger contact sprung outwwards, and the female is basically a tube. But it works on the same principle of multiple contact points - no matter which direction the shock or vibration acts in, there's contact being maintained.Hope that helps