8
\$\begingroup\$

When working with through the hole components, I have read that you should clip leads before soldering so the shock from clipping doesn't break the joint. On the other hand I've seen a ton of instructions for (more or less professional) DIY kits, where the picture depicted all components of a type being installed, then soldered, then clipped. The latter method is much faster and easier of course.

\$\endgroup\$
  • 5
    \$\begingroup\$ If you want NASA level reliability, cut and crimp the leads (bend them horizontal on the solder side) and then solder, but for most purposes clipping after soldering is fine. But don't try to clip multiple leads at the same time- that can put excessive force on the joints. \$\endgroup\$ – Spehro Pefhany Oct 23 '15 at 13:45
9
\$\begingroup\$

I was told to cut the leads to length before soldering. There was an IPC standard around on which basis we were taught that. I don't remember which standard it was exactly.

A reference I found is this document by IPC.

[...] The next part of the through-hole solder joint is the component lead. [...] Either way the leads are formed – usually with a 90 degree bend – and trimmed to the correct length. After the lead is trimmed, it may be clinched or bent over to hold the component in place during the rest of the assembly process. [...] The last part of the connection is the solder joint. [...]

So to prevent parts from falling off, you bent the already trimmed leads over (in a direction where it doesn't cause problems). And after that you solder them.

It is probably taught that way just as @GummiV mentioned in the comment, that the force and shock of the trimming might cause the joint or the PCB to be damaged.

I actually managed to break of a fragile ring with the track once because I was trimming after soldering, so I think the advice of the IPC is quite sound.

There are also frames around which help you in the assembly of through hole boards. You can put the board in, put all your components in from the top, then put down a lid and turn the whole thing around to solder on the bottom side.

Looks something like this:

enter image description here

\$\endgroup\$
  • \$\begingroup\$ What do you call the clipper machine holder in the picture above? I need one for some short run assembly. And where would I find one? \$\endgroup\$ – Dan Dec 17 '17 at 17:33
  • \$\begingroup\$ @Dan: I just used a sheet of foam (hand-held) to hold the components against the board when I flipped it for soldering - nothing fancy. \$\endgroup\$ – Peter Bennett Dec 17 '17 at 19:17
  • \$\begingroup\$ @Dan I think they go by the names of "mounting frame" or "soldering frame". I'm situated in Germany, so I could be completely wrong. Shop link \$\endgroup\$ – Arsenal Dec 18 '17 at 7:14
7
\$\begingroup\$

If you are interested in doing very high quality soldering I recommend you search for military soldering specifications. You will find instructions for bending leads with stress reliefs and to the proper radius. The leads should be inserted into the board and bent slightly, just enough to keep them in place during soldering. After soldering, you cut them off with cutters that have blades where the side toward the component is perpendicular to the lead. In other words, the angle part of the blade faces away from the board. Ordinary toe-nail clippers are the cheapest adequate illustrative cutter for this, but tend to wear more quickly than purpose-built cutters. If you examine toe-nail clippers you will see they are flat on the side that faces your toe and angled on the side that faces the cutoff nail. This is why your toenails don't shatter, crack, etc. when you cut them off, instead the cutoff nail gets enough energy to fly across the room into your coffee cup. If you use a cutter with blades like this, the shock will be transmitted to the cut-off lead and not to the board/lead/component.

\$\endgroup\$
  • 1
    \$\begingroup\$ These specialised clippers are absolutely the way to go. Not only do they prevent such shock issues, they also make cleaner cuts close to the joint. (Plus, they can be used for clipping finger nails...) \$\endgroup\$ – leftaroundabout Oct 23 '15 at 15:22
  • \$\begingroup\$ The mil specs require that the lead be clipped before soldering. In part, this is a reliability issue as (1) there is no unprotected copper that way, and (2) there is no localized severe stress to the finished solder joint. \$\endgroup\$ – Brock Adams Oct 24 '15 at 7:06
2
\$\begingroup\$

I've always been told to clip the leads after soldering to reduce the shock that gets transmitted to the part - this reduces the chance that the part will be damaged.

As well, how do you intend to manually cut and bend the component legs before inserting so perfectly that they fit and can be soldered? I can bend them fine, but getting the length right is just too fiddly. Bend, insert, solder, clip.

If you have a machine doing the work, then the question is moot. The machine will bend, cut and insert however it was built.

\$\endgroup\$
  • 1
    \$\begingroup\$ Indeed, I don't think it's possible to do a good job of clipping to length before soldering. You might trim excessively long leads for convenience, but you'll still have to trim after. \$\endgroup\$ – pjc50 Oct 23 '15 at 11:20
  • \$\begingroup\$ Thanks, I've always been doing it the "fiddly" way of trying to match the right length, clipping them, then try keeping them from falling out again etc.. This helps me a lot! \$\endgroup\$ – jilski Oct 23 '15 at 11:22
  • 3
    \$\begingroup\$ I believe there might be some confusion. The question doesn't specify that leads should be cut and bent before inserting, only before soldering. So the process goes: bend and insert -> cut to length -> solder. The idea is that if soldered before cutting the cutter exerts a force on the solder joint which might cause cracks to develop and joint going bad with time/vibration. \$\endgroup\$ – GummiV Oct 23 '15 at 11:50
  • 4
    \$\begingroup\$ @jilski You shouldn't be so quick in accepting answers, especially when it's prefaced with "I've always been told...". Although JRE's advice might be sound and correct, I would personally wait a few days to see if somebody might chime in with a reference to standards or best practice documentation, or maybe even industry experience with exactly this matter. \$\endgroup\$ – GummiV Oct 23 '15 at 11:53
  • 4
    \$\begingroup\$ Now I feel sorry for all those easily shocked components! Is it better to cut off their limbs before or after boiling them in molten metal? Who knows! \$\endgroup\$ – user65586 Oct 23 '15 at 13:33
2
\$\begingroup\$

One common process for industrial assembly of through-hole boards is:

  • Insert all the parts
  • Crop them all with a cropping machine (e.g. 'Cropmatic', though that might be a UK thing)
  • Wave solder them.

You couldn't wave-solder the board sensibly with all the leads still on anyway.

For a bit of hand assembly, if you're damaging things cropping the leads you just need to go and get a better set of side-cutters.

\$\endgroup\$
  • 4
    \$\begingroup\$ In my many years of the industry I have to say that through hole stuffing will entail forming and clip leads to a nominal length. Then insert components followed by wave solder. Only then is the lead cropping machine used to clip all the soldered leads to a uniform length. Think of the cropper as a lawn mower for the bottom side of the board. It will not work well if the leads are loose in their holes. \$\endgroup\$ – Michael Karas Oct 23 '15 at 13:31
  • \$\begingroup\$ I suspect the conclusion from all this is 'it doesn't matter much' \$\endgroup\$ – user1844 Oct 23 '15 at 16:30
1
\$\begingroup\$

40 years in the industry.. so, 1) clinch, clip and solder, or 2) clinch, solder, clip, and then RESOLDER. do not leave exposed base metal. corrosion can and will creep up through the metal until it causes the connection to fail.

\$\endgroup\$
1
\$\begingroup\$

J-STD-001 and IPC 7711/7721, both instruct you to cut to length and solder to prevent shock to the solder joint.

\$\endgroup\$
1
\$\begingroup\$

As a master instructor for IPC and previously the Navy it is always best to trim the leads before soldering. If trimmed after soldering per IPC J-STD-001 specs they must be either reflowed or inspected at 10 power magnification. Any time a solder connection is reflowed you stand a chance of reducing the reliability of the solder connection by increasing the thickness of the intermetalic layer which reduces strength.

\$\endgroup\$
  • \$\begingroup\$ It can be done before or after soldering, so long as its done with shear cutters (never diagonals) to avoid shock stress on the joint and the device. \$\endgroup\$ – hacktastical Jul 16 at 2:28
0
\$\begingroup\$

Another option is to solder components, clip them, and then reflow the solder. This has the advantage of easy initial soldering, easy clipping, a clean looking finish, and a solid bond. That being said for the strongest bond I would follow the other answers and clip first.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.