When breadboarding the length of the wires on resistors (through-hole) is quite comfortable. The same holds for other components like diodes or capacitors. I presume the terminal length was made to fit this application, because it essentially is similar to how, 60 years ago, valves were wired up with resistors "in the air" (without a pcb).

However, as virtually all through-hole resistors go into a pcb, terminals could be half the length. Or, if they were angled, they could have the correct length for pcb insertion. I have actually seen those, but I can't find them on digikey, for example, so I presume they are not common.

Copper is relatively costly and getting scarcer. The cutting of long terminals only seems to cause additional waste, therefore unnecessary recycling and/or environmental costs.

The question is: is there something holding back a transition to shorter terminals lengths, or would most machinery be able to accept it without problem? Restated: why haven't terminal wires been shortened a long time ago.

I get expect to get answers referring to cultural aspects, as standards reduce costs for everybody, but I am more interested in the underlying technical obstacles (to reducing waste). Would we be able to move on, or not? Why not?


closed as primarily opinion-based by pipe, RoyC, Warren Hill, Finbarr, PeterJ May 4 at 13:37

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    \$\begingroup\$ Do you think the "shorter terminal lengths" you are considering are met with the surface mount resistors that are used now? \$\endgroup\$ – Solar Mike Apr 26 at 12:45
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    \$\begingroup\$ Bandoliered components have the lead end contaminated with glue, which will cause a soldering problem, these have to be cut off. The market share of leaded components now, compared to SMD, is miniscule, and it's probably not worth retooling the remaining automatic cropping/bending machines that are still in the field. \$\endgroup\$ – Neil_UK Apr 26 at 12:53
  • \$\begingroup\$ @SolarMike Yes. But there are still 350000 active through-hole items (resistors alone) on digikey. \$\endgroup\$ – user103185 Apr 26 at 13:47
  • \$\begingroup\$ @Neil_UK Could perhaps another (glueless) packaging format be used? \$\endgroup\$ – user103185 Apr 26 at 13:48
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    \$\begingroup\$ The reason the wires are long is to support many different wire lengths with the same standard part. The wires are generally cut shorter and the length is user selectable. If they were shorter then manufacturers would need a second part to support those who needed a longer length for a specialised application. \$\endgroup\$ – KalleMP Apr 26 at 19:12

Through-hole components, other than power components, are not really a hotbed of innovation since they've largely been supplanted by SMT parts as of 20-30 years ago or so. The equipment, such as cutting machines, end cap crimpers and welding machines, is being run down and not replaced most likely.

In some old designs, resistors were mounted vertically, which required the long lead on one side anyway. In fact you could, at one time, buy resistors preformed to that shape with the long lead covered partially with lacquer.

Further, the standard packaging to fit automated assembly machinery is tape and reel, or ammo pack (Z-folded taped parts shipped in a cardboard box), which requires long leads with tape at the ends. Again, that stuff (referring to through-hole automated stuffing equipment) is generally not being replaced (image from here.

enter image description here

Bulk packed resistors might be used for manual assembly in very low end products, assembled in places with dirt-cheap labor rates, but that's hardly a growth market.

The leads are very seldom made of copper, rather they're made from plated mild steel, and you can easily confirm that claim with a magnet. Some SMT parts use copper leadframes rather than steel to increase thermal and electrical conductivity.

Back in the old days, for manual assembly, one could order resistors cut and formed to fit a PCB for a nominal additional cost (not through distributors but going directly to the manufacturer). It would cut down on shipping cost. The manufacturers ran their standard parts through a forming and cutting machine, but I think they bypassed the tape part (my memories of through-hole resistor factories is getting a bit hazy after all these years).

It might be interesting to quantitatively compare the waste percentage (by weight or volume) of modern parts like 0201 or 0603 resistors vs. tape and reel resistors. I'm guessing it might actually have gone up.

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    \$\begingroup\$ Quite a few through hole connectors have phosphor bronze cores. \$\endgroup\$ – Peter Smith Apr 26 at 13:11
  • \$\begingroup\$ No copper... I should have guessed, but I simply didn't imagine. It is a resistor so copper is of little use. This means my main argument has been nullified. \$\endgroup\$ – user103185 Apr 26 at 13:25
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    \$\begingroup\$ @user103185 At one time ordinary 1/4-W 5% Philips through-hole resistors were supplied with a very thin gold flash on the leads. But cost-cutting is relentless. \$\endgroup\$ – Spehro Pefhany Apr 26 at 13:37
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    \$\begingroup\$ @analogsystemsrf The spiral-cut element didn't help. \$\endgroup\$ – Spehro Pefhany Apr 26 at 14:38
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    \$\begingroup\$ @CaptainCodeman To prevent corrosion of the leads and improve solderability. \$\endgroup\$ – Spehro Pefhany Apr 26 at 17:10

Probably it's a matter of history. I assume you are mostly talking about through hole components. Some reasons why they have longer terminals:

  • Easier to solder
  • Easier to place (manually)
  • Easier to check the polarity (e.g. with LED diode where one side is longer than the other).

For SMD components the terminals are small or only small areas on the bottom.

However, there are some components where a minimal terminal lead is comfortable, such as components who are highly affected by temperature (temperature fuses for example).

Assuming waist reduction is mostly an issue for mass production, it is not an issue for through hole components, since companies already use (small) SMD technology.

  • \$\begingroup\$ About your point that SMD already offers short leads, therefore through-hole is already legacy: digikey has 700.000 SMD vs 350.000 through-hole resistors, so there still seems to be a quite significant demand. I might add that long terminals in my experience do not facilitate manual placement on a PCB. \$\endgroup\$ – user103185 Apr 26 at 13:19
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    \$\begingroup\$ @user103185 I'm afraid I don't understand you. I would say that longer terminals DO facilitate manual placement on a PCB. \$\endgroup\$ – Michel Keijzers Apr 26 at 13:26
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    \$\begingroup\$ @user103185 Compare total quantity of parts in stock rather than quantity of part numbers. For example, SMT T&R 5% resistors there are more than 80,000,000 in stock of 1K alone. \$\endgroup\$ – Spehro Pefhany Apr 26 at 13:30
  • \$\begingroup\$ @MichelKeijzers Consider rectangular capacitors which have ~10mm leads, they are much easier to place, then bend their leads a little to maintain them in position before soldering. Resistors on the other hand result in a forest of long wires protruding, and on a high density board demand to be cut a little before soldering. So I'd say the length of their leads isn't favorable. \$\endgroup\$ – user103185 Apr 26 at 13:40
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    \$\begingroup\$ @user103185 ... actually I like the long leads, because I don't use PCBs but I solder every component on proto boards, and the long wires of the resistor I can use to connect it to nearby or further away components. \$\endgroup\$ – Michel Keijzers Apr 26 at 14:23

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