How to solder very small parts. SMD installation: basics of soldering, soldering of printed circuit boards and technology. SMD installation at home. Hand soldering of miniature SMD elements

If you are too lazy to read the article, start immediately watching the video, which shows the process of making a soldering iron, its assembly and testing. Although, some technical details are covered only in the article. Video length 8 minutes, Full HD resolution. There are subtitles.

Prologue

I recently presented to the viewer a similar design of a soldering iron, but with half the power. It was a subminiature soldering iron, allowing for the smallest work, such as, for example, repairing cables.

Unfortunately, this design turned out to be too complex to be repeated, since it required the manufacture of all sorts of intricate parts, as well as special equipment for manufacturing heating element. Therefore, I decided to significantly simplify the homemade product, but at the same time increase the efficiency of the product.

It is appropriate to report here that several days of experiments with heating elements based on MLT resistors have proven the complete inconsistency of this design, although it is quite widely represented by home-made people on the Internet.

Only one resistor out of five made it possible to bring the tip temperature to 400°C, and then only during one on/off cycle. The next time it was turned on, it refused. Other resistors did not allow temperatures above 250°C and failed during one or two short cycles.

A study of failed resistors showed that the break of the film resistive element occurs along the outer perimeter of one or another contact cup. You can check this yourself if you connect a resistor to the power supply and use a voltmeter to determine the location of the highest voltage drop.

But don’t be discouraged, making a soldering iron based on an MLT resistor is also quite labor-intensive work, since modification of the resistor itself requires even primitive turning. And the design presented below can be repeated almost on the knee.

Soldering iron from a tin can

This is a sketch of a small-sized soldering iron for soldering SMD r/a components. This soldering iron was assembled using it.

Detailing

The soldering iron handle was made from a jump rope handle. Unfortunately, the pen was missing through hole, and it had to be drilled. The video shows how this can be done.

The sketch included self-tapping screws as fastening elements for fastening the case and cable, but I didn’t have such small screws at home. So I used hollow rivets that I cut threads into.

I glued the threaded bushings and a spring from a ballpoint pen obtained in this way epoxy glue into the holes drilled in the handle. If you use self-tapping screws, it is advisable to also drill holes for them so that the handle does not crack.

The frame of the soldering iron is a small tube bent from tin from tin can. A section was used as a template for bending the tube copper wire diameter 2.5mm. The same wire served as a blank for making a soldering iron tip. When using wire of a different diameter, you will have to make an amendment to the frame development drawing.

The body of the soldering iron is also made of 0.3mm thick tin from a tin can.

In order to ensure that when drilling holes with a diameter of 3 and 4 millimeters correct form holes and do not remove burrs, it is better to use drills with zapfenbor sharpening. The holes of the sizes indicated above are necessary to reduce the temperature of the body at the point of its connection with the soldering iron handle. The different diameters of these holes were chosen so that the bending line of the planks did not pass through the holes.

And this is a drawing of the developments: the body, the frame and the contactor. The drawing can be glued to the sheet metal and used as a template for cutting the outline and marking holes. Below the preview is a drawing in A4 format. Drawing scale 1:1, resolution 300 pixels per inch.

Technical data and calculation of the soldering iron heating element

A few words before the numbers.

A small-sized soldering iron should be low-voltage simply because the smaller the heating element, the more difficult it is to ensure electrical safety. This is due to the finite dielectric strength of air insulation.

In addition, the short length of the nichrome wire from which the low-voltage heater is made allows the use of single-layer winding. A heater of this design has better heat transfer and is easier to manufacture. This is primarily due to the fact that each successive layer of the heater requires the use of a heat-resistant gasket, which has a lower thermal conductivity than metal.

It is assumed that the temperature of the soldering iron will be regulated by changing the supply voltage, for example, using an amateur laboratory block nutrition.

Let's calculate the resistance of the spiral for a soldering iron with rated voltage 12 Volt.

Initial data:

Supply voltage – 0…12 Volts,

Power – 15 Watt,

The heater resistance will be equal to:

R = U²/P, Where:

R – resistance in Ohms,

U – supply voltage in Volts,

P – heater power in Watts.

R = 12²/15 = 9.6(Ohm)

I obtained a nichrome wire of a suitable diameter by disassembling a ten-watt resistor C5-5-10Watt at 160 Ohms. Inside there was a wire with a diameter of 0.17 mm.

By the way, metal case I used the same resistor in manufacturing

I did not anneal the nichrome wire, since the calculated wire length made it possible to wind the turns with some clearance (pitch). If you come across a thicker wire and the distance between the turns is too small, the wire will have to be annealed until scale forms.

You can determine the length of the wire using an ohmmeter. I got about 140mm.

The number of turns of the heater spiral is determined as follows:

ω = L/(π*(D+d)), Where:

ω – number of turns,

L – wire length,

π – Pi number (3.14),

D – diameter of the frame together with the insulating mica gasket,

d – wire diameter.

ω = 140/(3.14*(3.6+0.17)) ≈ 12(turns)

A soldering iron of the described design can provide a temperature at the tip of the tip of over 500°C. The time to reach a temperature of 350°C is about one minute.

Soldering iron assembly

The heating element spiral is wound on a tin frame. Between the frame and the spiral there is a mica (or glass fiber) gasket. To prevent the mica plate from falling apart when winding the spiral, it was glued to a piece of fiberglass. WITH outside the spiral is also insulated with several layers of fiberglass.

The terminals of the spiral are covered with a fiberglass tube, borrowed from an electric stove discarded by neighbors.

To ensure uniform clamping of the heater by the tin shell, a small tin contact is inserted into the gap in the shell. It prevents the glass fabric from being squeezed into the shell gap.

And this homemade soldering iron for soldering assembled SMD parts. The small distance between the front edge of the handle and the end of the tip ensures the necessary accuracy of tip positioning when installing small radio components.

Related topics

So, I decided to show how I solder SMD components (“Surface Montage Details” means surface mounting of parts). In general, for some reason, there is an opinion that soldering SMD components is difficult and inconvenient. I will try to convince you otherwise. Moreover, I will prove that soldering SMD components is much simpler than conventional TH components (“Through Hole” - through-hole components :)).

To be completely honest, TH and SMD components have their own purposes and areas of use, and attempts on my part to convince you that SMD is better are a little incorrect. Well, okay - anyway, I think you will find it interesting to read.

Do you know which one main mistake those who are trying to solder SMD components for the first time?
Looking at the small legs of the microcircuit, the thought immediately arises about what kind of thin tip you need to take in order to solder these small legs and not put “snot” between them. In the store we find a thin conical tip, attach it to a soldering iron, pick up a small drop of solder and try to solder each leg separately with a needle-tip. It turns out long, tiring and not neat. This approach seems logical, but is fundamentally wrong! And here’s why – soldering SMD components is helped by such “terrible forces” as surface tension, wetting forces, capillary effect, and not using them means making your life much more difficult.

How should everything go in theory? When the soldering iron tip is applied to the legs, the wetting force begins to act - the tin, under the influence of this force, begins to “flow around” the leg from all sides. The tin is “drawn” under the leg by capillary effect, and at the same time the contact pad under the leg and on the board begins to “wet”. Solder evenly “fills” the pad along with the leg. After the soldering iron tip has been removed from the legs and the solder is still in liquid state, the force of surface tension forms a drop from the solder, preventing it from spreading and merging with the neighboring legs. Like these ones complex processes occur during soldering. But all these processes happen by themselves, and all you need to do is bring the soldering iron tip to the leg (or several at once). Is it really simple?!

In practice, there are certain problems with soldering very small SMD components (resistors, capacitors...) they can “stick” to the tip during soldering. In order to avoid such a problem, you need to solder each side separately.

In order to achieve good soldering, you need certain materials and tools.
Main material, providing comfortable soldering, is a liquid flux. It degreases and removes oxides from the surface of the metal being soldered, which increases the wetting force. In addition, it is easier for solder to form a drop in the flux, which prevents the creation of “snot bridges.” I recommend using liquid flux - rosin or petroleum jelly flux do not give such an effect. Liquid flux is not uncommon in stores - buying it will not be a problem. It looks like clear liquid with a nasty smell reminiscent of acetone (the one I buy is called “F5 – flux for soldering fine electronics”). You can, of course, try soldering with alcohol-rosin, but firstly, the effect will be worse, and secondly, after removing the frozen rosin with alcohol, there remains white coating, which is very difficult to remove.
The second most important thing is the soldering iron.. It’s very good if there is temperature control - you don’t have to worry about overheating the components. Optimal temperature for soldering SMD components is in the range of 250-300 °C. If you don’t have a soldering iron with temperature control, then it’s better to use a low-voltage soldering iron (12v or 36v power 20-30w) it has a lower tip temperature. Most worst result gives a regular soldering iron for 220v. The problem is that the tip temperature is too high, which causes the flux to quickly evaporate and deteriorate the wettability of the soldering surface. The high temperature does not allow the leg to be heated for a long time, because of this, soldering turns into nervous poking with a sting at the board. As a partial way out of the situation, you can advise turning on the soldering iron through a power regulator (make it yourself - the circuit is quite simple, or buy a ready-made one - in a lamp store they are sold as dimmers for lamps and chandeliers).
Soldering iron tip must have an even working cut (this can be either a classic “hatchet”, such as a “screwdriver” or a 45-degree cut).

The cone tip is not suitable for soldering SMD components - do not solder with it, you will suffer. The “microwave” sting gives very good results. Who doesn't know - this is a sting that has work plane hole. With the help of this hole and the capillary effect created in it, solder can not only be applied, but also the excess can be effectively removed (after I tried microwave soldering, the remaining tips were lying around in the box idle).
Solder. No special solder is needed - use the one you usually use. Solder in a thin wire is very convenient - easy to dose. I have a wire with a diameter of 0.5mm. Do not use lead-free solder (they are trying to force electronics manufacturers to switch to it because lead is harmful). Due to the absence of lead in the solder, the force of surface tension is significantly reduced; soldering with a regular soldering iron will become problematic.
Still need tweezers. No special features here - Any will do convenient for you.

Soldering technology is very simple!
We place the SMD component on the contact pads, moisten it generously with liquid flux, apply the soldering iron tip to the component, the solder from the tip flows to the component contacts and the board pads, remove the soldering iron. Ready! If the component is very small or large (the tip does not grip both sides at the same time), solder each side separately, holding the component with tweezers.
If we solder a microcircuit, then the technology is like this. We position the microcircuit so that the legs land on their contact pads, generously moisten the soldering areas with flux, solder one outer leg, finally align the legs with the pads (the soldered leg allows, within certain limits, to “rotate” the microcircuit body), solder another leg diagonally , after this the microcircuit is securely fastened and you can safely solder the remaining legs. We solder slowly, running the tip along all the legs of the microcircuit. If jumpers have formed, you need to clean the tip from excess solder, generously lubricate the jumpers with liquid flux and go over the legs again. The excess solder will be picked up by the sting and the “snot” will be eliminated.

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Soldering SMD parts without a hair dryer

Everyone understands how you can use regular soldering iron EPSN, power 40 watts, and a multimeter, independently repair various electronic equipment, with output parts. But such parts are now found, mainly only in power supplies various equipment, and similar power boards where significant currents flow and there is high voltage, and all control boards are now based on SMD elements.

So what can we do if we do not know how to dismantle and solder back SMD radio components, because then at least 70% of possible repairs equipment, we won’t be able to do it on our own... Someone who is not very familiar with the topic of installation and disassembly will probably say that this requires a soldering station and a soldering hair dryer, various nozzles and tips for them, no-clean flux, type RMA-223 , and the like, what in the workshop home handyman usually doesn't happen.

I have at home a soldering station and a hair dryer, nozzles and tips, fluxes, and solder with flux various diameters. But what if you suddenly need to have your equipment repaired, on the road to order, or while visiting friends? And disassemble and bring the defective board home, or to a workshop where the appropriate soldering equipment, inconvenient, for one reason or another? It turns out there is a way out, and it’s quite simple. What do we need for this?

What is needed for soldering?

1. Soldering iron EPSN 25 watt, with a tip sharpened into a needle, for mounting a new microcircuit.

2. Soldering iron EPSN 40-65 watts with a tip sharpened to a sharp cone, for dismantling a microcircuit, using Rose or Wood alloy. A soldering iron with a power of 40-65 watts must be turned on via a Dimmer, a device for regulating the power of the soldering iron. You can have one like the one in the photo below, very convenient.

3. Rose or Wood alloy. We bite off a piece of solder from the droplet with side cutters, and place it directly on the contacts of the microcircuit on both sides, if we have it, for example, in a Soic-8 package.

4. Dismantling braid. It is required to remove solder residues from the contacts on the board, as well as on the chip itself, after dismantling.

5. SKF flux (alcohol rosin flux, crushed into powder, dissolved in 97% alcohol, rosin), or RMA-223, or similar fluxes, preferably based on rosin.

6. Flux Off flux residue remover, or 646 solvent, and a small brush with medium-hard bristles, which is usually used in school, for painting in art lessons.

7. Tubular solder with flux, 0.5 mm in diameter (preferably, but not necessarily this diameter).

8. Tweezers, preferably curved, L-shaped.

Wiring of planar parts

So, how does the process itself work? We bite off small pieces of Rose or Wood solder (alloy). We apply our flux liberally to all contacts of the microcircuit. We put a drop of solder on Rose, on both sides of the microcircuit, where the contacts are located. We turn on the soldering iron and set it using a dimmer, the power is approximately 30-35 watts, I don’t recommend it anymore, there is a risk of overheating the microcircuit during dismantling. We pass the tip of a heated soldering iron along all the legs of the microcircuit, on both sides.

Dismantling using Rose alloy.

In this case, the contacts of the microcircuit will close, but this is not scary, after we dismantle the microcircuit, we can easily remove excess solder from the contacts on the board and from the contacts on the microcircuit using the dismantling braid.

So, we took hold of our microcircuit with tweezers, along the edges, where the legs are missing. Typically, the length of the microcircuit, where we hold it with tweezers, allows us to simultaneously move the soldering iron tip between the tips of the tweezers, alternately on both sides of the microcircuit, where the contacts are located, and slightly pull it up with tweezers. Due to the fact that when melting a Rose or Wood alloy, which have very low temperature melting, (about 100 degrees), relative to lead-free solder, and even ordinary POS-61, and moving with the solder on the contacts, it thereby reduces general temperature solder melting.

Dismantling microcircuits using braid.

And thus the microcircuit is dismantled without dangerous overheating. On the board we have the remains of solder, Rose alloy and lead-free, in the form of sticky contacts. To bring the board back to normal, we take the dismantling braid; if the flux is liquid, you can even dip its tip into it, and place it on the solder “snot” that has formed on the board. Then we heat it from above, pressing it with the tip of a soldering iron, and run the braid along the contacts.

Soldering braided radio components.

Thus, all the solder from the contacts is absorbed into the braiding, transferred to it, and the contacts on the board are completely cleared of solder. Then the same procedure must be done with all the contacts of the microcircuit, if we are going to solder the microcircuit into another board, or into the same one, for example, after flashing using a programmer, if it is a Flash memory chip containing BIOS firmware motherboard, or monitor, or any other equipment. This procedure must be performed to clean the microcircuit contacts from excess solder.

After this, we apply the flux again, place the microcircuit on the board, position it so that the contacts on the board strictly correspond to the contacts of the microcircuit, and there is still some space left on the contacts on the board, along the edges of the legs. For what purpose are we leaving this place? So that you can lightly touch the contacts with a soldering iron tip and solder them to the board. Then we take a 25-watt EPSN soldering iron, or a similar low-power one, and touch the two legs of the microcircuit located diagonally.

Soldering SMD radio components soldering iron.

As a result, the microcircuit turns out to be “stuck” and will not budge, since the melted solder on the contact pads will hold the microcircuit. Then we take solder with a diameter of 0.5 mm, with flux inside, bring it to each contact of the microcircuit, and simultaneously touch the tip of the soldering iron tip, the solder, and each contact of the microcircuit.

I do not recommend using solder of a larger diameter; there is a risk of adding “snot”. Thus, we have solder “deposited” on each contact. We repeat this procedure with all contacts, and the microcircuit is soldered into place. If you have experience, all these procedures can actually be completed in 15-20 minutes, or even in less time.

All we have to do is wash off the remaining flux from the board with solvent 646, or Flux Off cleaning agent, and the board is ready for tests after drying, and this happens very quickly, since the substances used for rinsing are very volatile. 646 solvent, in particular, is based on acetone. Inscriptions, silk-screen printing on the board, and solder mask, and do not wash off or dissolve.

The only thing is that it will be problematic to dismantle a chip in a Soic-16 or more multi-pin package in this way, due to difficulties with simultaneous warming up, large quantity legs Happy soldering everyone, and fewer overheated microcircuits! Especially for Radio circuits - AKV.

There was a desire and need to move to more compact circuits than those assembled on a regular breadboard. Before thoroughly purchasing textolite, elements and microcircuits for surface mounting, I decided to try to see if I could assemble such a small thing. In the vastness of Aliexpress, there was an excellent “simulator” for very reasonable money. If you have soldering experience, there is not much point in reading the review.

The set is a light effect of running lights, the speed is regulated by a variable resistor.
Everything arrived in a standard bubble envelope, in a zip bag

Appearance of the set

Consumables

Soldering iron

I ended up using this healthy tip... It turned out to be very convenient for correcting crooked elements, since its size is enough to heat both soldering points, and then I was too lazy to change it.

Holders

third hand, heat shrink is put on the crocodiles so as not to scratch the PCB, and the board holds up much better


PCB Holder

A couple more photos

Soldering temperature – important point in the work of the solder, on whom the quality of the metal connection depends. This indicator should be higher than the similar indicator of complete melting of tinol. In some cases, the indicator may be between the liquidus line and the solidus line.

Based on theory, the solder must be completely melted before it fills the gap and is distributed in the joint under the influence of capillary forces. In this regard, the liquidus temperature of tinol can be the lowest used for a procedure such as high-temperature soldering. In turn, all parts must be heated to this temperature or higher.

You cannot be sure that all internal and external parts of the parts are heated only to a given temperature. Heating rate, location, mass metal parts, as well as the coefficient of thermal expansion of the soldered metal - all these are factors that determine the heat distribution in the part.

Under conditions of rapid local heating of parts temperature distribution unevenly, the temperature of the outer surfaces is significantly higher than the inner ones. During slow heating and uniform heat distribution, the distribution of thermal energy in the solder joint occurs more evenly.

Diffusion and dissolution of tinol during soldering

During wetting of the metal being joined with molten solder, dissolution of the base metal by tinol or diffusion of tinol components into the base metal may occur. On top of that, diffusion has highest probability formation if the tinol and the base metal are similar in chemical composition.

The following factors may influence dissolution and diffusion:

• Material joining temperature;
• Soldering duration;
• The geometry of the metal being joined, since it determines the area of ​​the base material exposed to tinol;
• Chemical composition.

In rare cases, during soldering, due to local diffusion of tinol between the grains of the base material, material spreading occurs, depending on internal stresses. Excessive diffusion of tinol in the base metal is likely to affect the mechanical and physical properties metal

Thus, the thin parts of the base material are the most vulnerable area solder connection. In this place, due to erosion, through sinks can form. It is worth noting that the dissolution of the base metal with tinol changes its liquidus temperature, thereby leading to insufficient filling of the gap between the parts.

To reduce diffusion or dissolution, there are several alloys that are used as tinols. Solders acquire a liquid consistency when the temperature reaches below the effective liquidus temperature. Thanks to solder of this composition, high-temperature soldering is also carried out successfully in those circumstances when the temperature of the metal connection has not reached the liquidus line.

SMD component connection temperature

Bottom heating makes it possible to reduce heat dissipation from the component to the SMD board, thereby reducing desired temperature soldering tool. When using air methods for replacing components, bottom heating can reduce or completely eliminate warping of the SMD board, which may well occur due to one-sided heating by hot air.

In addition, printed circuit boards made on ceramics require gentle preheating before the soldering procedure due to the sensitivity of these materials to temperature changes.

Based on the method of supplying thermal energy, we can distinguish infrared and convection bottom heaters. The first devices often consist of several quartz lamps, which have a pronounced red glow. Regarding convection devices, they can work by using forced convection.

The SMD components under consideration are quite fragile, and under conditions of vibration instability (mechanical shocks) they can crack. Another disadvantage of SMD components is their intolerance to overheating during soldering, which often causes microcracks that are almost impossible to notice. The most unpleasant thing, perhaps, in this matter is that you find out about cracks in SMD components during operation. You can check for cracks in SMD parts using an ordinary multimeter.

Thus, you can connect SMD parts using soldering station, as well as a soldering iron. Specific part solders claim that it is easier to solder components using a soldering station with a stabilized temperature. However, if there is no soldering station, you can resolve the issue using a soldering iron, turning it on using the regulator. It is worth noting that without a regulator on a conventional soldering iron, the temperature of its tip (tip) reaches a temperature of 400 degrees. The C. indicator when working with SMD components should be 260-270 g. WITH.

The optimal heating temperature of the soldering iron tip, as well as the required power during manual soldering, are indicators that depend on design features soldering iron and the task it performs. When working with lead-free tubular solders, which have a melting point of about 217-227 degrees. C, the minimum heating value of the soldering iron tip is 300 g. WITH.

During soldering, it is necessary to avoid in every possible way excessive overheating of the soldering iron tip, as well as prolonged exposure of the tip to the metal. In most cases, when working with lead-free solders and traditional tinols, it is most suitable to heat the soldering iron tip to a temperature of 315-370 degrees. WITH.

In certain situations excellent results when soldering SMD components, they can be obtained during short-term heating (the duration of exposure of the soldering iron tip is up to 0.5 seconds), as well as when heating the soldering iron tip to a value from 340 to 420 degrees. WITH.

The procedure for soldering SMD components

The procedure for soldering SMD components:

1. First, remove one of the contact pads. To do this, apply a sufficient amount of tinol to further form the fillet.
2. Next comes the installation of the SMD component on the gearbox.
3. The next step is to hold the SMD component with tweezers, and at the same time bring the soldering iron tip, thereby ensuring simultaneous contact of the soldering iron tip with the output of the SMD component, as well as the tinned CP.
4. Perform short-term soldering for 0.5-1.5 seconds. Regarding the tip of the device, it should be retracted.
5. Next, high-temperature soldering of the second terminal is performed: by bringing the tip of the device, you ensure simultaneous contact of the tip with the terminal and the gearbox.
6. Next, from the side opposite to the soldering iron tip, the tinol should be applied at an angle of 45° to the gearbox, as well as to the terminal of the component.

Four secrets - the key to successful soldering

There are four secrets to high-quality soldering and subsequent long-term operation of the part. Let's take a closer look at them.

Fundamentals of a quality connection:

1. Correct use of solder and flux in soldering;
2. The cleanliness of the soldering iron tip, as well as the degree of its heating;
3. Clean soldered metal surfaces during the procedure;
4. Correct connection, sufficient heating working area details.

As it becomes clear, a lot depends on the heating temperature of the parts, as well as the degree of heating of the soldering iron. You should also know the melting point of some tin-lead solders.

Melting temperature of solders

Knowledge of the technological component of soldering allows the solder to connect parts on for a long time, That is excellent quality for a true professional. Thus, high-temperature soldering will show excellent performance.