Step 4: Soldering components onto a circuit board

Picture of Soldering components onto a circuit board
soldering still 2.jpg
Up until pretty recently I spent most of my life soldering speaker wire and crossover components for speakers. This meant mostly wires twisted around wires or big resistor leads twisted around inductors and capacitors. At that level soldering doesn't really get any more complicated than what I did in the previous step. Lots of the projects on Instructables, however, use smaller electrical components and circuit boards, so I figured I would give that a try too.

Soldering on a circuit board takes a little more care and attention, but it's still very doable. I pushed a few of the leads from some spare LEDs and resistors that I had from my LEDs for beginners post through some open holes in a circuit board that was lying around. I soldered the leads onto the bottom of the circuit board where the electrodes push through. This is called through hole component soldering.

To solder the LEDs and the small resistors to the circuit board I switched to the adjustable temperature soldering iron. The tip was smaller so it would be easier to get the solder right where I wanted it, and using the soldering gun on a circuit board is probably way more heat than necessary and it could end up damaging the components. I set the temperature of the iron to 675 degrees Fahrenheit and waited for the tip to heat up. I then loaded the circuit board into the alligator clips and got myself ready to solder - iron in one hand, coil of solder in the other.

When soldering leads into circuit boards you want to heat the metal contact on the board and the lead itself. Applying too much heat can damage the circuit board or even your components. The surfaces being joined in this application were much smaller than the twisted wire, so things heated up a lot faster.

I touched the tip of the iron to the crack between the lead and the metal pad on the circuit board. After waiting a couple of seconds, I dipped the tip of the solder into the joint and placed a very small amount of solder at the connection - no more than the head of a pin or so.

Once the solder pooled a bit and soaked into the joint I removed the solder wire and then the iron. I remove the solder a second or two before I remove the iron so that the tip of the solder doesn't get stuck to the joint. The solder begins to harden as soon as you remove the iron.

Using the proper amount of solder is more important while soldering small components on a circuit board than when soldering wires. If you apply too much solder and it pools up outside of the metal pad, it can cause a short. Too little solder and your component won't make a good connection with the circuit board and might not work the way you want it to. When you've got the right amount of solder it looks like a small ant hill that forms right at the base of the lead and the circuit board.

Here is a video of the process.

mchazlitt1 month ago

FLUX...the secret of flow

DonL53 months ago

As a soldering instructor, the one thing I see often is people not knowing about the importance of FLUX. If your solder is balling up, not flowing where you want it, not gripping the wire, pad, or component, its because you did not use flux. The rule is that "solder follows flux". When flux is applied, and heated with the soldering iron before applying the solder, it does several things. It creates a thermal coupling to transfer heat quickly to the area you will be soldering, it removes and impurities and oxides that are on the metal surface, and it prepares the metal to bond with the solder. If you apply solder without flux, it can be easily removed by chipping it off or by vibration. If you apply flux first, your solder joint permanently bonds with the metal. It cannot be chipped off and even heating it again and wicking the solder off will leave the surface coated with solder because the solder is permanently bonded with the with the metal. For electronics, the recommended flux to use is RMA, which is a mildly active acid flux. It becomes active only when heated and the acid etches the metal allowing the solder to bond to the etching. Be sure to quickly clean the flux residue off and clean the solder joint.

sjones9811 months ago

Hi I've just finished a little soldering project but unfortunately its not working, I've just read your comment about not reheating solder, which I think I did a few times, how crucial is this and could this be the reason my circuit won't work? do you think I should start again? Thank you


I see that this is a bit late but the problem seems to be the soldering done on the board. There are a few areas where leads seem to overlap, which, of course, causes short circuits. I'm not the greatest at soldering myself, and I've done worse quite a few times; sometimes involving unpleasant explosions.

ageorgia4 years ago
Hi, this "through hole component" soldering is exactly what I've been trying to do. The DC jack on my laptop is broken, and I've been attempting to fix it. But for the life of me, I can't get the solder to behave the way yours does in the video, where you get the "ant-hill" shape.

When I do it, the solder either balls up on the end of the solder wire, or bunches up into a little blob around the lead, which is only a good enough joint to last for a week or so before I start losing the connection again. (I had the exact same problem while I was soldering the pickups in my guitar as well, although that was soldering a wire to a plate so it was quite different.)

So can somebody please tell me....WHAT am I doing wrong??
schans ageorgia8 months ago

I would check that you have a soldering iron that will heat up high enough first. It sounds like the components you are attempting to solder never get to the proper heat to allow the solder to flow. Heat is crucial. To much and the solder is not controlled and to little it will not stick to the components. Make sure you are applying heat to the component you are trying to solder and not the solder itself.

Ive had this problem myself and have found it to be that the contacts you are trying to connect are dirty and you probably need to flux them.

Hope this helps
belletinker2 years ago
Now I can make my own repairs once I get proper tools. Thank you, will save lts.
Bompata3 years ago
How can I tell if there is hole in the circuit board where the pad is? Do I have to try to push a wire through while the solder is melted?
The hole should be visible. If, by chance, you're salvaging or attempting to repair something, then the hole may be "plugged" with the old solder, and perhaps even the lead from the old component. In this case, desolder the joint first (using a desoldering braid - which is my personal modus operandi - or a desoldering pump (which come in various forms, such as quasi-mechanical spring-loaded variants that resemble a large hypodermic syringe, or as a simple squeeze bulb).

Another tip, which is especially crucial when working on salvaged board/components, is to never 'reheat' solder in an attempt to reuse it. Once the solder cools and dries the first time, its "done". Don't reheat it in an attempt to 'reshape' it, or add more to it, just remove it and start again. Old solder loses many of its core attributes if reheated (and often goes from a shiny finish, on first application, to a more matte finish once reheated - stick with shiny).,
CyborgGold4 years ago
I did a how to solder a pcb search on google which brought me here. I am tryig to solder a few points on an xbox 360 controller, but the soldering points are not bare, there is nothing but a hole where I need to connect some wire. Would you mind letting me know what I can do to get the wire to stick? Thanks!
ATTABOYSLIM5 years ago
 I am very glad to see this post and appreciate the fact that you took us, the "Rookies" into consideration while explaining. Here is where I'd like to see a better example; I'm getting better at reading Motherboards (computers), for example but have no clue how to follow the path. I mean, at times, it looks like one squiggly line and every single spot is connected to it and that is baffling to me. I guess I look at it in a way that says, "This and these go to the thing over there and combined, they make that thing on the other side work." 

The reason it works with everything connected to the same flow path is beyond my knowledge. So, when you talked about soldering onto a motherboard using the 'Thru Hole" (i guess you called it) method, my eyes started glazing over. Obviously that wouldn't be a problem  and the advice perfect if my theory of "All connected to one" were accurate but I somehow doubt that to be the case.  So, maybe you could show an application that repaired a broken circuit that could be re-soldered.

I realize that sounds moronic. If I can't understand the circuit pattern than how will I know if one  is broken? It  did to me, for a moment also but the truth is that I have had far more need to re-connect instead of creating one. It's actually more like, repairs -  10  &  New circuits - 0. Just thought I'd ask.
if everything is attached to one lead, its probably the return. All of the circuits can be connected to the return without any problems(so long as its big enough to handle the current)
Thank you for this tutorial, I am trying to figure out the right and wrong ways to solder, and your detailed instructions are very concise.  lots of soldering tutorials have instructions like 
" heat up the piece and stick the silver wire to it and your done.  easy huh...."
It's nice ot get some quality insruction. thank you again for your time making this tutorial for us newbies!!

sevir6 years ago
In my opinion; using an alligator clip to hold a pcb is a risky endeavor because of the circuit paths, if you scratch that then your pcb isn't quite so nice any more
zemuro sevir5 years ago
 i agree. but you can insert the "jaws" of the clip into pieces of isolation tube. simple mod, but it helps!
Bradlez926 years ago
what are "leads?"
sevir Bradlez926 years ago
"Leads" are the wires that protrude from the component
endolith8 years ago
"Up until pretty recently I spent most of my life soldering speaker wire and crossover components for speakers." We solder stuff around speakers all day at work, and our soldering irons kept dying. Turns out the Wellers use a piece of magnet as a thermostat. When it goes above its Curie point it temporarily loses its magnetism and stops pulling on a switch, which breaks the electrical connection. Guess what happens to that sensor when you solder next to a big speaker magnet? The magnet dies and the soldering iron burns itself up. So we got a different brand and I like them better for other reasons, too.
rachel8 years ago
I have also heard the "hill" referred to as a Hershey's kiss. You want the solder blob to look like a mini-Hershey's Kiss with a wire sticking out the top. I like this mnemonic b/c kisses are wrapped in silver foil, similar to the look of a solder joint. Also, your joint should be shiny, not dull - dullness indicates that the solder did not attach well. You can often fix this simply by re-heating the area until the solder flows again.
All my life I've searched for a woman who solders circuit boards... Rachel will you marry me?
Dunno... can you cook?
i see an instructable on "how to be an online stalker" in someone's future.... :)