This article is about soldering for show. While usually you solder electronic components to make the best possible connection and keep everything working, this is just to make a great visual result. If you want to take photos from your projects or would like to impress a customer with a nice looking prototype, you have to solder with more care to the detail.
In the next sections I will describe a few things which are worth to think about, using Boldport Project #4 as an example. If you have any questions or suggestions, feel free to add a comments to this article. Also feel free to ask about any other technique I use, about which you would like to see another article.
To get great results you need the right tools.
First, you really need a good soldering station. The brand does not matter, but the performance does. The solder iron should actually transfer the required heat to the solder joint and this in a very consistent and reliable way. For this reason, the temperature sensor should be as close to the tip as possible. I personally use products from the Weller WT Series.
For the shiny solder domes, you need a pliers with a flush cut (often called flush cut trimmer). You will see, there are pliers in a wide price range and they look very similar. The main difference is the maximum hardness and thickness of wire they can cut – and how durable they are. Cheap pliers get blunt after a few number of cuts and you can only cut very soft wires. Wires from LEDs often kill this cheap pliers instantly. More expensive plies can cut harder and thicker wires and stay sharp over a very long time.
Here I recommend the pliers from Erem (e.g. the 632N shown in the photo above). To begin with, they are expensive, but they are very durable and can cut very hard metals easily, without getting blunt. Also they use a special mechanism to get an equal force open the blades, you will notice this if you have to use this pliers over a long time.
To get shiny solder domes, sadly you need solder which contains lead. Like the Stannol S-Sn60Pb40 HS10 shown here. This is a very soft solder with halogen activated resin, which is non-adhesive. I use this kind of solder just for photographed devices. It creates very nice and shiny solder points and the remaining flux can be easily removed.
Any solder wire should work, but the ones containing lead will create very shiny solder domes. I recommend a solder wire with the formula Sn60Pb40 (60% tin, 40% lead). If you like to use lead free solder, I can recommend Sn95Ag4Cu1, solder wire containing silver and copper which gave me the best results. Just avoid Bismuth (Bi) in solder, it will never produce nice results.
To get clean results, you need a clean and tidy working place – especially if you plan to do macro photographs from the device. Wires and tools can scratch the solder mask of the PCB, dust and dirt from the working place will stick on any component and the PCB. Often this is not visible from naked eye, but later on the photos every scratch and dust particle will be a problem. While dust and dirt can be cleaned, the scratches will not disappear.
You should start by preparing all required components. Cut any components from tapes, make sure they are clean and have straight wires. Bend all wires to the correct sizes, using a round pliers. You need a very small round pliers which creates a nice round corner at the bending point. This also prevents the wire from breaking. Check if all component wires are correctly bent and fit into the PCB.
For this example project, no bending is required. Just cut the wires from all resistors to exactly the same length, so that all resistors are perfectly in the center (both ends have the same length for all resistors).
Arrange all components in a logical order. If you have different values of components which are hard to distinguish, put them on a paper and write the values beside the components.
The goal of this step is to let you focus on the soldering work and keep distractions as small as possible.
Make sure your solder iron has the right tip for the solder points you do. I suggest, better a little bit smaller than required. Also clean the tip so there is no burned stuff on it. While soldering, clean the tip regularly – always keep it as clean as possible. Use brass metal wool to clean the tip, no sponge. The sponge will cool the tip and remove solder from it. Brass metal wool will remove any dirt from the tip, without cooling it down. There is also always a rest of solder covering the tip.
I will explain all soldering using the Boldport Project #4. Most technique can be applied to any other project.
I start with the lowest components on the board. In this case this are the small LEDs. Here I use the PCBite holder to fasten the PCB and use some foam to press the components tightly to the board. I verify if they are tight to the board by pulling on the wires. There should be no leeway and the component should not move if I pull on the wire.
Usually you would bend the wires to the side to hold the component into place. The problem with this technique is, that it will be harder to cut the wire as close as possible to the board. This is required for the solder domes as explained later.
Now you can solder the components into place. Use only very little solder. As much as you need to keep the components in place. It does not matter if the solder pad is not fully covered in solder.
Next you cut the wires as close as possible to the board, also cutting any solder from the board. In the photo above you can see how flat the wire is cut off and you see the wire which still has some solder on it. Here you really have to care how you cut the wire. Make sure you only cut just over the solder pad and not touching the solder mask anywhere. Otherwise you will get nasty scratches.
Now you resolder each cut solder point. Turn the temperature of your solder iron at least 20ºC above the right temperature for the used solder. Now add more solder to the solder point and keep the tip on the point until you see the solder is freely flowing. Add more solder until you get a nice dome. Then quickly remove the tip of the solder iron from the solder dome.
If you do it right, you will get perfectly shiny solder domes. If you get spikes, you are probably do something wrong:
- Make sure you are over the recommended solder temperature. This is important to keep the solder a little bit longer in fluid state to form the dome.
- Remove the tip of the solder iron very quickly. The heating has to be go from maximum to zero in almost no time.
- Make sure there is enough flux. Add more flux to the spot to fix the problem, e.g. using a flux pen. Alternatively you can just cut the current dome off the board and start new.
Repeat the same procedure for all LEDs.
For the surface mount components, in this case the switch, put some solder on one pad.
Now place the switch on the pad, carefully center all pins on all pads and reheat the solder on the pad. This can look ugly, just ignore it, it just has to fasten the component into place. Check again: Are all pins of the component exactly in the middle of the pad.
Add solder to each pin, start with the opposite one. Make sure the solder flows regularly around the pin and sticks on the pad. Quickly remove the tip of the solder iron and check if the solder forms some kind of dome. If not, add more flux, reheat, until it does.
Repeat the same for the battery holder.
To solder the resistors into place, put two of them into their holes and put something with a regular surface under it, so both are perfectly on the same height.
- If you solder components in a PCB, use the same some logical orientation for all components. For example the tolerance ring of all resistors should point in the same direction. The label of all other components should point into the same direction.
- Make sure you perfectly center resistors and capacitors on the board. If they are in a line, make sure they build a perfect line.
Next solder the two resistors into place, cut, resolder until you have a nice solder dome. Repeat for all resistors. Make sure you keep whatever you placed under the resistors in place, until the resistors are soldered into place at the correct height – otherwise they will slid out of the hole.
Build some ring using wire and carefully arrange the other ends of the resistors, so they touch but not cross.
Put solder on the iron tip, move it closer, until physics will suck the solder between the two wires. Avoid touching them.
Now each resistor is secured at a second point, we can take care of the top side solder pad. Add a tiny bit solder and let the solder equally flow around the wire and cover the pad.
This can change the shape of the solder dome on the bottom side. Make sure to check each dome and fix the shape if necessary.
Remove all cut-off wires and other tools from your desk. Clean your desk thorough from dust, wires, solder and flux blobs.
Now use isopropyl alcohol and foam swabs to remove any flux from the PCB and components. Make sure to check also the wires and component surfaces.
If you plan to do macro photography of the board, never use cotton swabs. They leave small cotton threads everywhere which are almost invisible for the naked eye. For this reason I switched to the more expensive, but more efficient foam swabs.
Never use kitchen roll to clean any surfaces. This will create tiny scratches which will be visible on any macro photo. Always use either cotton based products, or you can use products suitable to clean photography lenses.
If you have to bend wires, always use some template to bend them. This will create a very regular and symmetric look. Just use e.g. a large pen or something else cylindrical to get the right shape. Round pliers are another great way to get smaller arcs in a defined way.
You should get a very clean looking object.
I hope this article was useful. If you have any questions or suggestions, feel free to add a comments to this article. Also feel free to ask about any other technique I use, about which you would like to see another article.