Regardig the wire leads that come out of a plastic LED package - Page 1
Forum section: electronics / general

author: xrunner
author_rank: Super Contributor
timestamp: May 11, 2015, 10:06:45 pm
content: This seems like a weird question, but I always thought the wire coming out of most through-hole eletronic components was tinned copper. However, I just cut the leads of a common LED shorter and for whatever reason I looked at the cut ends of the lead wire under a high power magnifier. I didn't see any copper. I even filed the end flat to make sure but all I see is silver. Bright shiny silver. Is the wire some sort of silver alloy? I just never thought about it before.

author: JBaughb
author_rank: Regular Contributor
timestamp: May 11, 2015, 10:14:59 pm
content: Copper is expensive. I would imagine they used some sort of custom alloy. Possibly Nickel based, I'm not sure exactly.

author: gibbled
author_rank: Regular Contributor
timestamp: May 12, 2015, 04:03:39 am
content: Stick to a magnet?Likely steel.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 12, 2015, 04:49:07 am
content: Steel is the most common for discrete components, yes. It's stiffer, and for the short lengths used, hardly more resistance than the PCB traces connecting them (and yes, this includes bare jumpers used for 1 and 2 layer boards, which you might assume should be reasonably conductive as they cover some length).Steel is easily tinned directly, so it's cheap to deal with as well. Copper often needs a nickel diffusion barrier layer, e.g. for silver and gold plating.Components that use copper leads either have to, or are just better that way. Example, hard copper lead frames for semiconductors. There are MOSFETs available today which are almost as much Rds(on) due to the leadframe as the die itself. Small ceramic disc capacitors are usually soft copper -- likely annealed by part of the manufacturing process that requires heating the assembly, and which cannot tolerate steel for reasons (oxidizes too easily, reacts with other metals or the ceramic in the process?). (In contrast, leaded MLCCs are probably always steel, because they are merely SMT chip capacitors with leads tacked on, then dipped in epoxy.)You'll also see silver or nickel platings in teflon or high temperature wires. The nickel is magnetic, but the core may be copper.Nickel is much more expensive than copper, and has no electrical advantage over iron, so it would not be used in bulk unless for other reasons. Vacuum tubes were made largely from nickel (as well as iron, copper, molybdenum, tungsten and others), which is mainly because it's easy to use in a hard vacuum (it absorbs little gas, so time and expense was saved on pumping and sealing the vacuum).Tim

author: rs20
author_rank: Super Contributor
timestamp: May 12, 2015, 04:52:54 am
content: Quote from: T3sl4co1l on May 12, 2015, 04:49:07 amDon't forget that PCB traces are remarkably thin, almost two-dimensional, whereas these LED pins we're talking about have a square cross section -- in other words, they are comparativelyverythick. So steel can be 10 times higher resisitivity and still have a lower resistance over the same length and the same track width.

author: tautech
author_rank: Super Contributor
timestamp: May 12, 2015, 05:04:34 am
content: Decades ago when I used to scavenge TH components from PCB's they were all copper and I just presumed as much until ~10 years ago when I inadvertantly moved a magnet over some lead snippings on the bench. Yep they are steel these days.

author: G7PSK
author_rank: Super Contributor
timestamp: May 12, 2015, 07:23:09 am
content: Sorry iron is the usual material for component leads has been for many years, I have some 1960s transistors with iron leads.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 12, 2015, 07:48:26 am
content: Rustistors as I call them. Hey what circa 1960 RCA transistor is that which is open circuit? No idea, it's completely brown. No wait, it's a rustistor! (Followed by wild guessing of an equivalent)

author: G7PSK
author_rank: Super Contributor
timestamp: May 12, 2015, 08:17:10 am
content: Quote from: smjcuk on May 12, 2015, 07:48:26 amBut they don't resist rustthey rust if you so much as look at them, so they cannot be rustsistors.

author: smjcuk
author_rank: Frequent Contributor
timestamp: May 12, 2015, 08:19:13 am
content: Quote from: G7PSK on May 12, 2015, 08:17:10 amRustuctors?

author: xrunner
author_rank: Super Contributor
timestamp: May 12, 2015, 11:58:29 am
content: Quote from: T3sl4co1l on May 12, 2015, 04:49:07 amSteel huh? Well I didn't know that. Indeed the LED wire is attracted to a magnet. I was thinking it wouldn't be steel (as in stainless steel) but of course stainless steel can't be soldered so I ruled out steel. But plain steel can be soldered - well, well ...

author: SeanB
author_rank: Super Contributor
timestamp: May 12, 2015, 05:36:38 pm
content: Steel, easy to stamp and cold form and above all cheap. As LED lead frames are made in massive quantities, and you sell the complete unit for under a cent, with the most expensive part being the LED die and gold bond wires inside. Steel is, as said above, easy to plate with tin. You do it in a continuous process after stamping, with it being chemically cleaned, pickled, washed and then electroplated in baths. Then you roll it up, and send to the manufacturer to epoxy the die to it and encapsulate. The scrap is then sent for recycling into more leadframes.

author: rdl
author_rank: Super Contributor
timestamp: May 12, 2015, 06:05:26 pm
content: I keep a couple of small trays with common parts handy on my bench. Out of curiosity I checked them with a magnet. Almost all the LEDs, resistors and capacitors had magnetic leads. None of the TO-220 parts did though (Some LM-317 and other regulators plus a couple of transistors) nor did any of the random (3904/3906/2222) TO-92 transistors. Strangely, none of the trimpots were magnetic either (most were Bourns 1/4" single turn, but some unknown brands also).