Earthing. Why crimp and not solder? - Page 1
Forum section: electronics / beginners

author: ptp170
author_rank: Contributor
timestamp: October 13, 2014, 10:46:14 am
content: This one has tickled my curosity again since seeing Dave's speaker box tear down. I've done a couple of searches on here and on Google and haven't really come up with an answer.Why does one crimp an earthing connector and not solder it??TIAChris

author: ludzinc
author_rank: Unknown
timestamp: October 13, 2014, 10:51:01 am
content: A proper crimp is a cold weld, and more reliable that a soldered joint.That said, a soldered joint is waaaay better that a crappy crimp!The problem with a soldered joint is that the wire is made inflexible (where the solder wicks up the wire), and any movement of the cable will fatigue the joint and lead to cracking, and worse case breaking of the wire.Yes, it's an extreme condition that will see a soldered joint fail, but a proper crimp will last in the same situation.Also, just soldering onto the frame as per the White Van Speaker teardown, is just a poor, mechanically weak way to do it.

author: ptp170
author_rank: Contributor
timestamp: October 13, 2014, 11:00:59 am
content: Thanks ludzinc. Thought it may have been something like that but also thought it might be something to do with the flux in the joint.Cheers for clearing that up for me

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: October 13, 2014, 11:05:49 am
content: Because soldering is easier to do badly in production. It's hard to mess up a crimp done with the right tool.

author: ptp170
author_rank: Contributor
timestamp: October 13, 2014, 11:14:50 am
content: It's about creating consistancy then as well

author: ciccio
author_rank: Frequent Contributor
timestamp: October 13, 2014, 11:20:45 am
content: Safety regulations require that safety ground conductor (and also all mains carrying conductors) be connected both electrically and mechanically (the electrical connection is not allowed to be subject to mechanical stress). Crimping the wire with an eyelet or a faston terminal connected to metal frame with adequate precautions assures both electrical (crimping the conductor) and mechanical (crimping the insulation) compliance.You could solder the wire to the eyelet, but you should at least turn the wire inside the soldering hole and make something similar to a knot, and this before soldering. It's complicated and time consuming.This is done on some products I've seen, but I'm not sure that this will comply with all standards.I'm pretty sure that soldering the wire to the frame is NOT compliant.Best regards

author: ptp170
author_rank: Contributor
timestamp: October 13, 2014, 11:30:34 am
content: That soldering direct to the frame looked as dodgy as hell anyway. I've seen Dave comment in some previous videos that soldering to an earthing lug was a no-no in his books also. Think it may have been the Hakko ripoff or the hot air rework station video?

author: N TYPE
author_rank: Regular Contributor
timestamp: October 13, 2014, 12:30:48 pm
content: If you want a really top dog connection you can always crimp a lug onto the wire and then feed solder into the crimp connection... then you get the best of both worlds

author: KJDS
author_rank: Super Contributor
timestamp: October 13, 2014, 12:50:16 pm
content: Quote from: N TYPE on October 13, 2014, 12:30:48 pmThat's fine unless solder wicks up the wire away from the crimp, in which case it leaves the wire brittle.

author: David Hess
author_rank: Super Contributor
timestamp: October 13, 2014, 01:04:59 pm
content: Quote from: ludzinc on October 13, 2014, 10:51:01 amThey make special tools (antiwicking tweezers?) to prevent this. It is an issue when tinning leads as well.Quote from: N TYPE on October 13, 2014, 12:30:48 pmIf I use a crimp connection this is what I do although the wicking problem noted above is an issue.I agree with ciccio. It is just cheaper to do it with only a crimp. Lots of older test equipment used a positive mechanical connection which was then soldered.

author: nanofrog
author_rank: Super Contributor
timestamp: October 13, 2014, 01:24:06 pm
content: Quote from: N TYPE on October 13, 2014, 12:30:48 pmGenerally speaking, not recommended IME.The heat anneals the copper terminal, which reduces mechanical strength. Solder wicking up the wire and reduce flexibility is also an issue. Either is bad, but combined, is a huge no-no. Do keep in mind though, I'm posting this from an aerospace background, where vibration is a significant consideration (similar for automotive applications).As per the anti-wicking tweezers, you'd have to crimp first, then solder if you actually want to generate a cold weld between the wire and terminal. Don't see them working well in that situation.

author: David Hess
author_rank: Super Contributor
timestamp: October 13, 2014, 02:41:12 pm
content: Quote from: nanofrog on October 13, 2014, 01:24:06 pmI am sorry if I was not clear. That is the order I use; crimp and then solder. Of course if the crimp is done properly then I agree that soldering is usually irrelevant and just provides an opportunity for other problems. For other than production work, I always suspect bad crimps unless soldered but I have occasionally found bad crimps in production work anyway although usually when they were the cause of failure.QuoteDo copper and copper alloys anneal at such a low temperature? I have had to use a torch in the past for this.Most of the terminals I have used were soft copper but the star ones are hard (kovar?) for obvious reasons. If the heat from soldering to a hard terminal was a problem, then I would have expected this to be an issue with the ones intended to be soldered to.

author: Monkeh
author_rank: Super Contributor
timestamp: October 13, 2014, 03:48:13 pm
content: If you solder a crimp you may as well just have soldered in the first place. The crimp no longer serves a function and the joint is now weakened at the transition from flexible copper to solder.

author: SeanB
author_rank: Super Contributor
timestamp: October 13, 2014, 03:49:52 pm
content: Speaking from avionics that is why all your multiplug connections are crimped, not soldered, unless it is inside equipment. The crimp connections stand up to vibration very well. often still having good crimp strength when vibration has actually worn the pin and socket side of the connector to the point where the pin has broken due to wear and the socket has worn through and split into pieces. Major fun to repair after a few years when you have to replace an entire wiring loom section because the small amount of extra cable left to enable you to remove the connector and box has shrunk down to the point where it no longer will reach.Pilot comes in complaining tail is "twitchy", and you open the panel to get to the control box, undo the connector and the pins all fall out onto the afterburner shield.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: October 13, 2014, 03:59:58 pm
content: I don't think the admonition against soldering a crimp is so much to do with that, as disturbing the joint. Filling it with another metal introduces a different expansion rate material, and also adds a galvanic corrosion concern (though you'd be hard pressed to solder with something that will actually encourage copper to corrode, any corrosion is unsightly at the very least).Supposedly, pure copper does in fact anneal (at least partially) at lower temperatures than alloys, but I think I'd still be surprised if much changed at soldering temperatures. That's in terms of stress holding the joint together (hard to measure externally, though you could set up a "typical process" example test) and crystalline / microstructure change (which can be determined with a destructive test).As an interesting side note, there are materials where you're required to compromise: the best way to solder large Litz cables (say, 10AWG down to #4-0 and the like) is to crimp the (fresh, cold, still enameled) wires in a lug, then submerge the lug in a solder pot until the bubbling stops. This is only possible with solderable enamels, of course (but, if you've purchased ten thousand strands of unsolderable polyimide, one hopes you've already thought about what you're doing). Almost certainly, such a joint is not "cold welded", but personally, I can't think how else you'd do it without expensive and hazardous chemicals, so this would be one of those exceptions.Tim

author: nanofrog
author_rank: Super Contributor
timestamp: October 13, 2014, 07:28:41 pm
content: Quote from: David Hess on October 13, 2014, 02:41:12 pmYes. You can anneal copper at 700F/371C.To fully anneal you will need more time, say on the order of ~30min, but even the short time of a solder joint can in fact relax some of the work hardening that's been performed in a terminal (crimped or not), even if just a small amount.Regarding solder terminals, alloys can be used to shift the temperatures upward of course. But the differences in their mechanical design from crimp terminals is what really distinguishes them, as they don't rely on work hardening for their mechanical properties (i.e. machining used to produce them instead of stamping).

author: coppice
author_rank: Super Contributor
timestamp: October 14, 2014, 01:26:48 am
content: Quote from: SeanB on October 13, 2014, 03:49:52 pmThroughout military electronics solder is only used when some form of crimp is not practical. Crimp always beats solder for reliability by orders of magnitude. As you said, this is especially true where there is strong vibration. However, I'm puzzled by your tale of connectors wearing away. That happens a lot when inappropriate connectors are used - e.g. ones with flat mating surfaces, which vibrate laterally until all the metal has gone. However, the time tested military connectors hardly ever fail like this.

author: hamster_nz
author_rank: Super Contributor
timestamp: October 14, 2014, 01:45:00 am
content: Somewhat related link, from NASA, on how to do it:http://workmanship.nasa.gov/lib/insp/2%20books/links/sections/201%20General%20Requirements.htmlCrimping is an efficient and highly reliable method to assemble and terminate conductors, and typically provides a stronger, more reliable termination method than that achieved by soldering..

author: huggy
author_rank: Newbie
timestamp: October 14, 2014, 12:25:41 pm
content: Quote from: ptp170 on October 13, 2014, 10:46:14 amI would solder the wire that was already crimped tight to start with, then use a bolt for attachment of the crimp connection.

author: con-f-use
author_rank: Unknown
timestamp: October 14, 2014, 01:31:13 pm
content: Quote from: ptp170 on October 13, 2014, 10:46:14 amAs was said: crimping is mechanically more stable and can take corrosion better. You want your earth connection to be as unbreakable and last as long as can be. Otherwise people die.

author: Tandy
author_rank: Frequent Contributor
timestamp: October 14, 2014, 02:13:08 pm
content: Also don't be tempted to tin the ends of multistrand before crimping you will end up with probably the worst of both worlds. The solder is soft, so may deform in time loosening the connection.

author: lpc32
author_rank: Frequent Contributor
timestamp: October 14, 2014, 02:44:56 pm
content: Speaking of which, can anyone suggest a cheap but decent terminal crimper from CN/HK sources (eBay or other stores)?

author: coppice
author_rank: Super Contributor
timestamp: October 14, 2014, 02:55:16 pm
content: Quote from: huggy on October 14, 2014, 12:25:41 pmSo you crimp and get a robust connection. Then you add solder, which will wick up the multi-strand wire. Even if you use a tool to limit wicking, you will get some. Now you have a fragile connection, that will break with very few bends or with some long term vibration. Why would you ruin a good crimp?

author: G7PSK
author_rank: Super Contributor
timestamp: October 14, 2014, 03:34:02 pm
content: I think that the reason crimping is considered better than soldering is due to tin erosion of copper. Tin in solder erodes or dissolves into copper causing embrittlement, copper age hardens which means that in order to anneal it you need to quench immediately after heating it in order to maintain the crystalline structure, it will revert back to the hardened state over a period of time any way but will be softer in the meantime. Heating from soldering will not anneal copper but will speed the age hardening. The faster you cool from anneal heat the more of the soft crystalline state is preserved. Since the ROHS regulations have been introduced the tin problem is worse than before.

author: SeanB
author_rank: Super Contributor
timestamp: October 14, 2014, 06:00:52 pm
content: Quote from: coppice on October 14, 2014, 01:26:48 amRight connectors, right sockets, right crimp tooling just right next to a great big afterburner shell, which does tend to create a lot of vibration in operation. If you are using a burner that will go through 20kl of fuel per hour ( note you will not get an hour at full taps with any tank on the plane, it will run dry fast) it tends to vibrate a lot. Was a known issue with high hour count airframes, where you would also have issues with cracking of the airframes as well. wiring looms were very well supported there as well, well laced, sleeved and with a lot of loom clamps. Would have been nicer located elsewhere, but that was where the actuators had to be.

author: huggy
author_rank: Newbie
timestamp: October 15, 2014, 06:18:18 pm
content: Quote from: coppice on October 14, 2014, 02:55:16 pmThanks for the tipnow i know not to solder it when crimped.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: October 16, 2014, 03:10:29 am
content: OTOH, 9 times out of 10 the other end of the wire is soldered to a lug....

author: oldway
author_rank: Super Contributor
timestamp: October 16, 2014, 08:35:59 am
content: Quote from: ciccio on October 13, 2014, 11:20:45 amI think you are probably right but I did not find any such safety regulations ...what are the standards that prohibit to solder the ground wire in domestic appliances? (if they exist...)As the main cable seems to be securely attached (it can not turn nor be pulled), it could also be objected that the ground wire can not undergo mechanical stress.So the requirement of its mechanical fixation would not be justified.In the practice, I don't think it's more dangerous.You see a cold solder at once, but a bad crimped wire is not so easy to detect: you have to pull the wire with a well-specified force to see if it will not release: it's a basic quality control practice. (NB: I never seen Dave doing this !)Nasa especifications for equipments intended to withstand accelerations and vibrations of a Saturn V rocket have nothing to do with an audio amplifier.According to IEC 61180, the device must be able to withstand a dielectric strength test of 2Kv rms for 1 minute between the transformer primary and the earth.Dave did not make such a test but he found that the transformer is bad quality and has not enough insulation between primary and secondary...This amplifier would never be compliant with IEC 61180, and for this reason, it is not only a crap amplifier, but also a dangerous one.

author: Neilm
author_rank: Super Contributor
timestamp: October 16, 2014, 06:12:48 pm
content: Quote from: oldway on October 16, 2014, 08:35:59 amI don't know about that sort of equipment, but I know IEC61010 explicitly states that wires are not held by solder alone.

author: SeanB
author_rank: Super Contributor
timestamp: October 16, 2014, 06:31:19 pm
content: Soldered to earth terminal, but only after the wire is inserted into the hole in the lug, and bent over for mechanical strength. Often you see the crimped wire with a pin that is riveted to the PCB and then soldered, giving a mechanical join that is additionally soldered. In this case the wire is still crimped and not soldered, but only the riveted joint is soldered.

author: ciccio
author_rank: Frequent Contributor
timestamp: October 16, 2014, 08:08:55 pm
content: Quote from: oldway on October 16, 2014, 08:35:59 amI do not have more recent documents on hand, but I quote from UL60065 (Audio Video and Similar electronic apparatus - Safety requirements). It is equivalent to IEC60065I'll quote only some parts of two paragraphs.15.3.2 For apparatus with non-detachable MAINS supply cords, the connection of the individual conductors to the internal wiring of the apparatus shall be accomplished by any means that will provide areliable electrical and mechanical connection, except that the supply conductors and the protective earthing conductor of a non-detachable MAINS cord or cable shall not be soldered directly to the conductors of a PRINTED BOARD.Soldered, crimped and similar connections may be used for the connection of external conductors. For soldered or crimped connections, barriers shall be provided so that CLEARANCES and CREEPAGE DISTANCES cannot be reduced to less than the values specified in clause 13 and annex J respectively, should the conductor break away at a soldered joint or slip out of a crimped connection. Alternatively, the conductors shall be positioned or fixed in such a way that reliance is not placed upon the connection alone to maintain the conductors in position.15.3.4 For the purpose of applying the requirements for MAINS supply cords:– it is assumed that two independent fixings will not become loose at the same time;–conductors connected by soldering are not considered to be adequately fixed unless they are held in place near to the termination, independently of the solder.However, "hooking-in" before the soldering is, in general, considered to be a suitable means for maintaining the conductors of a MAINS supply cord in position,provided that the hole through which the conductor is passed is not unduly large;– conductors connected to TERMINALS or terminations by other means are not considered to be adequately fixed unless an additional fixing is provided near to the TERMINAL or termination; this additional fixing may clamp both the insulation and the conductor.In the old days, I've done terrible things, like soldering PE conductor from IEC socket to a lug that was mounted to the metal frame using the pop rivet that held the same IEC socket, and that was considered acceptable (in fact there were no regulations to obey) and now, after 35 years, the the resistance to ground is still acceptable (I check when I do some maintenance to old timers), but now we must follow standards.Best regards

author: Tandy
author_rank: Frequent Contributor
timestamp: October 16, 2014, 09:11:50 pm
content: Solder is structurally weakFrom an old reference book..Tensile strength of rolled copper: 12 tons/sq. inTensile strength of cast solder 64Sn/37Pb: 4 tons/sq. inIt shows that solder can not be relied on for structural purposes. It is essential that the earth connection is the last to fail, imagine for example you trip over a cable and that breaks the retaining clip on the cable pulling it from the chassis and you then go and pick up this electrical device that that you just yanked on the floor touching exposed metal that is now live because the earth has come out. Typically the earth wire is always longer than the Live and Neutral wires so that it is the last to be subject to stress and the most securely fastened conductor.You could argue that there is no exposed metal on the wood and plastic junk box that Dave tore down but that is not the point good practice should be followed at all times.