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Soldering for beginners

Soldering for beginners
Soldering for beginners
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I've finished electrotechnics and microelectronics courses at university. I can assemble simple electronic devices and invent my own ones. My brother also helped me giving advices. If you don't want to deal with analogue signals, you can use one of the lots of different microchips and remain on top in digital electronics.

Let's work. Today everything will be about soldering. I know that many beginners who want to play with microcontrollers are afraid of soldering. At first you can use layout boards where you only stick the details into the panel like constructor.

Breadboard counter example

So you can assemble a very “curly” device.

Breadboard complex example

But sometimes we want to create finished device. In this case it is not necessary to create a circuit board. If there are not a lot of parts we can use a layout board.

Breadboard solderless

We have to solder in any case. But the question is how? Especially you have never soldered before. I will tell you about how to solder without any problem.

Until now I did it this way: I took soldering iron (I used a spatula type nose), solder and rosin. For soldering I took a little of solder on the soldering iron and put it into rosin. While it boils I tried to solder parts quickly (parts must be already inserted). After a few moments of heating the solder must move to the right place.

But this method didn't work. Parts heated, but solder didn't move from the soldering iron. The problem was in the catalyst, i.e. rosin. Putting the soldering iron into rosin wasn't enough to start the soldering process. While you're dragging the soldering iron to solder joints, all rosin burns. That's why I did not understand why flux is added into some types of solder. Because it burns while you picking it up.

I experimented and found several ways to improve the process:

  • Tin solder joints before soldering. But for delicate parts like microchips it isn't actual, because their contacts are already tined.
  • Put a little of rosin on solder joint. Then you touch the rosin with soldering iron and solder easily moves to the joint and the reaction starts on the right place. But after this circuit board is stained with burned rosin. Rosin is an insulator, but it does not allow seeing soldering defects. That's why we have to wash circuit board, but it is too difficult. In this way I soldered Maximite.
  • Use liquid flux. You might put a drop of liquid flux on (it is stronger than rosin) and then will be an active soldering process. But some problems may arise. Not all liquid fluxes are insulators and you also have to wash circuit board with acetone. And those that are insulators still remain on the board, spread over it and can interfere during board testing. In any way we have to wash the circuit board.

So, we have almost reached the goal.

The tool we need for soldering simple components is a normal soldering iron with awl shape nose:

Soldering iron

and solder with flux inside

Solder with flux

READY!

Everything is in technique. We have to do it in this way:

  • Detail is inserted into the board and should be fixed there.
  • Take the soldering iron into one hand and the solder into the other (comfortably if it is in special dispenser like in the picture).
  • You should not take the solder with the soldering iron.
  • Touch the joint with the end of soldering iron and heat it. It takes 3-4 seconds usually.
  • Then you touch heating joint with the solder without taking away the soldering iron. In fact, at this point all three parts are in contact: the soldering element and its hole on the board, soldering iron and solder. After a sec. you can take away soldering iron with solder and blow.

The most important part is to supply solder and flux directly to the joint. Solder with flux inside provides as much flux as we need. So we will not need to wash the circuit board.

Soldering

Of course you will need a minimum practice to solder by this method and no more. I am sure that every beginner could create the Maximite in about an hour.

I remind basic features of a good soldering:

  • Too much solder doesn't mean the quality of contact. A drop of solder at joint should cover it from all sides. It shouldn't have potholes, but also shouldn't be overly large bulb.
  • Soldering joint should be more gloss than matte.
  • If circuit board is double sided and its holes are non-metalized, then you should solder them out from both sides using this technology.

Everything is told below applies to soldering elements, which are inserted into mounting holes. The process of soldering planar elements is more difficult, but real. Planar elements take less space, but require more precise positioning of the joint areas.

Planar elements (of course not the smallest ones) are easier for soldering. But we have to tin the circuit board for each new device, because it is difficult to use prototyping board with planar elements.

Now I tell you about soldering of planar elements like microchips, transistors, resistors, capacitors etc. At home there are objective limits on the size of the elements, which we can solder with ordinary soldering iron. Below I list what I soldered using awl type soldering iron.

For soldering of planar elements we cannot use solder “on fly”, because it could solder together nearest feet of microchip. In this case you should use liquid flux for tinning soldering areas.

Phase 1

Put a little of liquid flux on each soldering area. Take solder with soldering iron and easily touch each soldering area with it. Only a little of solder will move on each place.

Phase 2

Take the element with tweezers. First of all it is more comfortable and tweezers take the heat from microchip and it is very important in case of planar elements. Put the element on its soldering area holding it with tweezers. You should hold the microchip's foot you want to solder. Heat sink is very important for microchips, so it would be better to use two pair of tweezers. With one pair of tweezers you hold the element and the other pair you fix on the microchip's foot (you could buy tweezers with holder). With your other hand put a drop of liquid flux on soldering joint (it is possible a little of flux gets on chip). Take the soldering iron and touch the soldering joint for a second. Repeat this procedure for each foot of the microchip. You can add a drop of liquid flux if needed.

SMD Soldering

Buying liquid flux you have to buy liquid circuit board cleaner. It is better to wash the board with circuit board cleaner after using liquid flux.

I am not a professional neither an advanced plumber. Everything you see above I made using ordinary soldering iron. Professionals have their own methods and special equipment.

For successful soldering of a planar element you will need much more soldering experience. Soldering of planar elements is real at home. Only microchips are difficult to solder them. But microchips can be bought already sealed into the pads or in the form of finished assemblies.

Here are pictures of everything I ever soldered after I gained some experience.

This is the simplest type of housing. You can put them into the pads, which are also very easy for soldering. You can solder them using my first instructions.

PDIP

SPDIP

These are more complicated. You should use second instructions with liquid flux and with accurate heat sink.

SOIC

QSOP

Simplest planar elements such as resistors below, could be quite simply soldered:

SMT Resistor

These ones are totally out of my possibilities.

PQFP

TSOP

SSOP

Some cheap, but very useful things that are worth to buy in addition to soldering iron, solder, tweezers and clippers:

Suction. Have you put more solder than you wanted or soldered wrong place? In this case you can use suction and remove it very easily. With one hand you heat with soldering iron the solder joint and with your other hand you use the suction. When the solder become liquid you simply push the button. All unused liquid solder will be removed.

Solder pump

Glasses. When you work with microchip legs and wires it can happen that the heated feet pops out and the solder flies to anywhere, it is possible to your eyes. This is not a joke.

Soldering safety glasses

 Good luck in the soldering! The smell of rosin - it's cool!



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