I have some questions about soldering I'm hoping to be helped out with. I have been soldering for a couple of years now, but I'm just not happy with the way it comes out some times. I'm comfortable with through-hole soldering, no problems there. I have been practicing surface mount, and will continue to do so, and it seems I will be able to pick that up with more practice.

The situation I seem to be having the most trouble with is soldering two wires together. Specifically, I am trying to solder wires onto transistor leads. My method is as follows: tin the strands of the wires, line up the wires with the transistor leads by use of the "helping hands" tool, and bring the iron with one hand and solder with the other up to the connection. Then, apply solder to the joint and wait a second for it to cool.

This seems to be the most common method, however I can't make a connection I'm happy with. It's either bunchy, or the wire moves, or the solder doesn't stick well, etc. Can anyone relate to this and have advice/suggetions? By the time I'm done soldering the three joints, I fear I have heated up the chip far too much. This brings me to another question: can I reduce the lifetime of the chip by giving it too much heat? In other words, can it still work after soldering, but fail a month or two later?

When soldering wires together in a situation like this, one method that works and gives a result that looks good is as follows: apply a glob of solder to the tip of the iron, hold the wire on the transistor lead in place, and then "paint" the solder onto the joint. However, I don't think this method is trustworthy because the solder which makes the connection has no flux. Is it best to not use this method, even if the wires are perfectly lined up and the solder looks smooth on the joint?

Thanks for reading and for any responses. I would really appreciate your help.

 

The step you're missing is tinning the wire. Generally it works best to use stranded copper wire for this type of connection. Before lining it up with the transistor lead, apply the iron to the wire and slowly add solder so that it evenly coats the exposed copper. It should cover it neatly, and leave you with a solid, silver-colored wire end. Once that's done, you line it up with the transistor lead and apply heat and solder and it should work much better.

As for soldering chips, I highly recommend using IC sockets, instead of soldering directly to the chip's pins. This eliminates the possibility of overheating the chip (assuming you don't plug it into the socket before soldering).

NEVER "paint" solder onto the wire. This creates a cold joint, which not only doesn't give a good mechanical connection, but the electrical connection will not be satisfactory either.

Hope this helps!
Regards,
Matt

 

If the wires are first twisted together, then the solder will naturally wick between both wires and solidly bond them.

Here's a rule to think about: a good solder joint begins with a good mechanical joint.

 

If the wires are first twisted together, then the solder will naturally wick between both wires and solidly bond them.

Here's a rule to think about: a good solder joint begins with a good mechanical joint.

It may be a bit difficult to twist a wire and a transistor lead together....

If you're soldering stranded wire to stranded wire, sure, twist them together. Otherwise, it's a bit tougher to do that way.

 

Matt, that's good advice, but I believe I did mention I'm tinning the wire. I've also tried tinning the leads of the transistor, the results are the same. Many times I have done the "paint" method by first tinning the wire and the lead, and then joining those two with solder that is on the tip of the iron. This way there is still flux, but like you said it's a dodgy method and it's best not to do it.

Ernie, I think that's a very good point to think about. For this application, it won't really work unless I don't tin the tips of the wires, which I haven't tried.

 

I use 2 clothes pins and a piece of thick paper. Attach each solderable piece to the paper with one clothes pin for each piece. Line them up and solder the result.

 

Your on the right track with tinning. Tin the wire and tin the transistor lead. There's an old saying... The bigger the blob the better the job. It's meant as humor, it's not true at all. The solder has to "stick" to both parts this requires heat and flux. Flux is the magic sauce! I have it in pens, tubes and bottle with brush. Get it and use it. Rosin core flux solder is recommended but use the above mentioned flux too. I've been in situation where the only flux I had was in the solder and the solder wasn't sticking to a terminal (or whatever) so I ran 3 to 6 inches of rosin core flux in to the joint to let the flux do it's cleaning. Clean off that mess then solder the joint cleanly. Iron temperature is a factor. Too much and your over heating stuff, too little an you can't heat a larger thermal mass like 16 gauge wire. For what you're doing there, I usually tin the wire and leave the solder just a little bit thick on the wire. Tin the transistor lead cleanly. Then clean the soldering iron on a damp sponge, apply just a tiny, tiny bit of solder to the iron to make a bead to help transfer heat. Bring the wire and lead together apply the iron to the wire, this will reduce the heat build-up on the component. When the solder on the wire melts it will melt the solder on the lead too. As soon as they blend together remove the iron. If the solder on the wire won't melt you don't have enough solder on the iron to transfer the heat. A touch of flux on the wire helps transfer the heat too. A bare clean iron tip is never good, it's real hard to transfer heat to the parts. As for overheating the parts, the data sheets often have limits but I've never damaged a part from soldering it as far as I know. I remember a guy showing me how the gain on a transistor increases with temperature by holding a butane lighter to it for over a minute. That transistor must have been over 1000° C, it kept on truckin'.

 

I tried so many solder wire brands that I know it's sometimes the solder composition or the contained flux that makes it difficult.

Row headers are much easier actually with lead solder.

Some chinese solder wire brands are difficult to use even with years of experience. The flux is next to nothing, and it takes very long for the solder joint to harden. I have to try 6 or 7 times sometimes.

In such a case, I add a bit more expensive solder with good flux.

Soldering wires to PCBs or other wires of different making, you must tin them both with the same solder wire. Makes it more easy.

Never put solder on a tip then paint or stick it to a joint.

Always first heat the joint, then add solder wire to it. You add the solder wire to the joint, not the iron. Sometimes a bit between the two...

Point tips are almost useless, as you can make a point tip holding a rectangular tip at an angle.

Flux is not always needed but you should have it available. For SMD it is required for the finer pitch ICs. Otherwise you can try minutes and have nearly no chance to get out the tin between the pins. Add flux generously, and you can easily pull it off with the tip.

0.8mm or 0.5mm needs a desoldering pump first. Use a high-quality all metal made pump for the best result. Better than desoldering wick. As you can reload these very fast. Some bits will remain but then apply more flux, and pull them off with the tip.

Over time, you would develope techniques which takes the least effort, and takes as little time as possible.

Always pull wires a little, twist component leads a little, and look with a magnifying glass. Bad joints are really nasty trouble source.

If you use cheap chinese lead solder, you'll have bad joints sometimes even if the wire is almost embedded in solder.

Beginners should stick to branded western stuff. I mean I have to add a bit more expensive solder wire sometimes to get the joint done.

The TFT display was done with cheap chinese solder, not much difficult here, but can be very nasty at times.

 

Do you have an "extra hands" holder?

These are vital to hold the wire steady, or hold the part steady, then you hold the other part in your hand and apply solder to join them (after tinning of course).

I have a couple and they are amazingly useful, especially since you can change the angle they hold things, to help gravity flow the solder or to give you the most comfortable access angle.

 

Well said takao. I hadn't thought about solder and flux quality as I'm using stuff I bought many years ago. I have had that experience with soldering copper pipe for plumbing though. Through that flux right in the trash after two attempts. I knew i sucked right off but a new guy would wonder for weeks what was wrong. If your starting out buy quality solder and flux to get a feel for how it should be... experiment from there.

 

Well said takao. I hadn't thought about solder and flux quality as I'm using stuff I bought many years ago. I have had that experience with soldering copper pipe for plumbing though. Through that flux right in the trash after two attempts. I knew i sucked right off but a new guy would wonder for weeks what was wrong. If your starting out buy quality solder and flux to get a feel for how it should be... experiment from there.

The bad chinese solder on the other hand works better for row headers. A hobby store maybe sells just one type, most recognized brands have 30, 40 or 50 different types. Halogen free flux is a must when you don't have a means to filter your air.

The rosin is not really bad in hobby quantity, but halogen containing flux is never good to inhale.

You really only need to filter the air when you solder each day as part of your job (these jobs are largely gone now).

 

You get what you pay for eventually.

 

If your starting out buy quality solder and flux to get a feel for how it should be... experiment from there.

Well, Spam is a bit of a problem here I see. Is there a way to flag it?

 

One way to do such a soldering is at first to produce marginally crappy solder joints to secure the component in place, then resolder each properly.

Once you have one pin secured, it stays in place, and if you use solid wire, does not move much. If you do it right, it is all hold together by tension. Then heat up again, and add solder.

 

Thanks for all the responses. I switched my iron over to a chisel tip, and did a couple of practice runs this morning. I attached a photo, take a look if you want. I would think this is considered to have good connection, but let me know your thoughts. Maybe the green wire is a little questionable given that solder doesn't flow around it as much as the other two. Thanks.

 

Soldering metal, requires three adequate elements... Cleanliness, Flux, and heat - in that order.
Stranded wire ? do a "Western Union " splice, paste flux, and enough heat to make the connect in 1/2 second dwell time.

Stranded wire around a transistor lead ? Twist the wire around a common sewing pin to create a "tunnel " slip that over the lead, holding the loose end and twist the wire to tighten the tunnel... apply solder flux, solder and heat 1/2 sec dwell.

Alligator clips make marvelous temporary heatsinks clipped on component leads. Between them, and short dwell time, you have no worry of scorching components.

 

Well, Spam is a bit of a problem here I see. Is there a way to flag it?

Usually it's best not to quote the spam post, and instead hit the red triangle button at the top of the post. That's a "report" button, for use in this exact situation.

 

Here's a rule to think about: a good solder joint begins with a good mechanical joint.

I use tinned solid wire and make small hooks on the wire and transistor leads then hook them together, squeeze the joint with long nosed pliers then solder.

Timescope

 

I use tinned solid wire and make small hooks on the wire and transistor leads then hook them together, squeeze the joint with long nosed pliers then solder.

Timescope

I've done that as well. Works like a treat

 

The rules of soldering are:
1/ Make the joint solid mechanically.
2/ Then make a good soldered joint.

The tip of putting loops in the transistor leg and the wire is a good one.