SMD designation on the board. See what "SMD" is in other dictionaries. SMD diodes and SMD LEDs

SMD - Surface Mounted Devices - surface mount components - this is what this English abbreviation stands for. They provide a higher installation density compared to traditional parts. In addition, the installation of these elements and the manufacture of a printed circuit board turn out to be more technologically advanced and cheaper in mass production, so these elements are becoming increasingly widespread and are gradually replacing classic parts with wire leads.

Many articles on the Internet and in print publications are devoted to the installation of such parts. Now I want to complement it.
I hope my opus will be useful for beginners and for those who have not yet dealt with such components.

The publication of the article is timed to coincide with 4 such elements, and the PCM2702 processor itself has super-small legs. Supplied complete PCB has solder mask , which makes soldering easier, but does not eliminate the requirements for accuracy, absence of overheating and static.

Tools and materials

IN amateur conditions It is most convenient to solder such parts using a special soldering gun or in other words - a hot-air soldering station. The choice of them on sale now is quite large and the prices, thanks to our Chinese friends, are also very affordable and affordable for most radio amateurs. Here's an example of this: made in China with an unpronounceable name. I have been using this station for three years now. So far the flight is normal.

And of course, you will need a soldering iron with a thin tip. It is better if this tip is made using the “Microwave” technology developed by the German company Ersa. It differs from a regular tip in that it has a small depression in which a drop of solder accumulates. This tip makes fewer sticks when soldering closely spaced pins and tracks. I highly recommend finding it and using it. But if there is no such miracle tip, then a soldering iron with a regular thin tip will do.

Factory soldering SMD parts produced by the group method using solder paste. Apply to the prepared printed circuit board on the contact pads. thin layer special solder paste. This is usually done using silk-screen printing. Solder paste is a fine powder of solder mixed with flux. Its consistency is similar to toothpaste.

After applying solder paste, the robot lays out the right places necessary elements. The solder paste is sticky enough to hold the parts. Then the board is loaded into the oven and heated to a temperature slightly above the melting point of the solder. The flux evaporates, the solder melts and the parts are soldered into place. All that remains is to wait for the board to cool down.

You can try this technology at home. This type of solder paste can be purchased from cell phone repair companies. In stores selling radio components, they also usually have it in stock now, along with regular solder. I used a thin needle as a paste dispenser. Of course, this is not as neat as, for example, Asus does when it manufactures its motherboards, but here it is. It will be better if you take this solder paste into a syringe and gently squeeze it through a needle onto the contact pads. You can see in the photo that I went a bit overboard by plopping down too much pasta, especially on the left.

Let's see what comes of this. We place the parts on the contact pads lubricated with paste. In this case, these are resistors and capacitors. This is where thin tweezers come in handy. It is more convenient, in my opinion, to use tweezers with curved legs.

Instead of tweezers, some people use a toothpick, the tip of which is slightly coated with gumboil to make it sticky. There is complete freedom here - whatever is more convenient for you.

After the parts have taken their position, heating with hot air can begin. The melting point of solder (Sn 63%, Pb 35%, Ag 2%) is 178C*. I set the hot air temperature to 250C* and from a distance of ten centimeters I begin to warm up the board, gradually lowering the tip of the hair dryer lower and lower. Be careful with the air pressure - if it is very strong, it will simply blow the parts off the board. As it warms up, the flux will begin to evaporate and the dark gray solder will begin to lighten in color and eventually melt, spread, and become shiny. Approximately as seen in the next picture.

After the solder has melted, slowly move the tip of the hair dryer away from the board, allowing it to gradually cool. This is what happened to me. The large drops of solder at the ends of the elements show where I put too much paste, and where I was greedy.

Solder paste, generally speaking, can be quite scarce and expensive. If it is not available, then you can try to do without it. Let's look at how to do this using the example of soldering a microcircuit. To begin with, all contact pads must be tinned thoroughly and in a thick layer.

In the photo, I hope you can see that the solder on the contact pads lies in such a low mound. The main thing is that it is distributed evenly and its quantity at all sites is the same. After this, we moisten all the contact pads with flux and let it dry for a while so that it becomes thicker and stickier and the parts stick to it. Carefully place the chip in its intended place. We carefully combine the pins of the microcircuit with the contact pads.

Next to the chip I placed several passive components - ceramic and electrolytic capacitors. To prevent the parts from being blown away by the air pressure, we start heating from above. There is no need to rush here. If it’s quite difficult to blow off a large one, then small resistors and capacitors can easily fly all over the place.

This is what happened as a result. The photo shows that the capacitors are soldered as expected, but some of the legs of the microcircuit (24, 25 and 22 for example) are hanging in the air. The problem may be either uneven application of solder to the contact pads or insufficient quantity or quality of flux. You can correct the situation with a regular soldering iron with a thin tip, carefully soldering the suspicious legs. To notice such soldering defects you need a magnifying glass.

A hot air soldering station is good, you say, but what about those who don’t have one and only have a soldering iron? With the proper degree of care, SMD elements can be soldered with a regular soldering iron. To illustrate this possibility, we will solder resistors and a couple of microcircuits without the help of a hair dryer with just a soldering iron. Let's start with the resistor. We install a resistor on the pre-tinned and flux-moistened contact pads. To prevent it from moving out of place during soldering and from sticking to the soldering iron tip, it must be pressed against the board with a needle at the time of soldering.

Then it is enough to touch the tip of the soldering iron to the end of the part and the contact pad and the part will be soldered on one side. On the other side we solder in the same way. There should be a minimum amount of solder on the soldering iron tip, otherwise it may get sticky.

This is what I got with soldering the resistor.

The quality is not very good, but the contact is reliable. The quality suffers due to the fact that it is difficult to fix the resistor with a needle with one hand, hold the soldering iron with the second hand, and take photographs with the third hand.

Transistors and stabilizer chips are soldered in the same way. I first solder the heat sink of a powerful transistor to the board. I don’t regret the solder here. A drop of solder should flow under the base of the transistor and provide not only reliable electrical contact, but also reliable thermal contact between the base of the transistor and the board, which plays the role of a heatsink.

During soldering, you can slightly move the transistor with the needle to make sure that all the solder under the base has melted and the transistor seems to be floating on a drop of solder. In addition, excess solder from under the base will be squeezed out, improving thermal contact. This is what a soldered integrated stabilizer chip on a board looks like.

Now we need to move on to a more complex task - soldering the microcircuit. First of all, we produce again precise positioning it on the contact pads. Then we lightly “grab” one of the outer terminals.

After this, you need to again check that the legs of the microcircuit and the contact pads match correctly. After this, we grab the remaining extreme conclusions in the same way.

Now the microcircuit will not go anywhere from the board. Carefully, solder all the other pins one by one, trying not to place a jumper between the legs of the microcircuit.

Surface mount technology originated in the 1960s and 20 years later became widely used in electronics manufacturing.

Now this technology is the undisputed leader. It is difficult to find a modern device that is not made using this technology.

First, let's understand the terminology.

Surface mounting is abbreviated as SMT(from English S urface M ount T echnology- Surface mounting technology (in Russian, - TMP)).

It is so well established that the abbreviation SMD sometimes also means surface-mount technology itself, although in fact the term SMD has a different meaning.

SMD- This S urface M ount D evice, that is, a surface-mounted component or device. Thus, SMD should be understood specifically as components and radio components, and not as a technology as a whole. Sometimes SMD elements are called chip components, for example, a capacitor chip or a resistor chip.

The whole point of SMT technology is to mount electronic components onto the surface of a printed circuit board. Compared to the technology of mounting components through holes (the so-called THT - T hrouth H ole T echnology), - this technology has many advantages. Here are just the main ones:

There is no need to drill holes for component leads;

It is possible to install components on both sides of the printed circuit board;

High installation density, and, as a result, savings in materials and reduction in the dimensions of finished products;

SMD components are cheaper than conventional ones, have smaller dimensions and weight;

Possibility of deeper production automation compared to THT technology;

If for production SMT technology is very beneficial due to its automation, then for small-scale production, as well as for radio amateurs, electronics engineers, service engineers and radio mechanics, it creates a lot of problems.

SMD components: resistors, capacitors, microcircuits are very small in size.

Let's get acquainted with SMD electronic components. For beginning electronics engineers, this is very important, since at first it is sometimes difficult to understand all their abundance.

Let's start with resistors. Typically, SMD resistors look like this.

Usually on their small-sized case there is a number-letter marking in which the nominal resistance of the resistor is encoded. The exception is microscopic resistors on the body of which there is simply no room for its application.

But, this is only if the chip resistor does not belong to any special, high-power series. It is also worth understanding that the most reliable information on an element should be found in the datasheet for it (or for the series to which it belongs).

And this is what SMD capacitors look like.

Multilayer ceramic capacitors ( MLCC - M ulti L ayer C eramic C apacitors). Their body has a characteristic light brown color, and markings are usually not indicated.

Naturally, there are also electrolytic capacitors for surface mounting. Regular aluminum capacitors They are small in size and have two short terminals at the plastic base.

Since the dimensions allow, the capacitance and operating voltage are indicated on the housing of aluminum SMD capacitors. On the side of the negative terminal on the upper side of the case there is a semicircle painted in black.

In addition, there are tantalum electrolytic capacitors, as well as polymer ones.

Tantalum chip capacitors are mainly made in yellow and orange color. I have already talked about their structure in more detail on the pages of the site. But polymer capacitors have a black body. Sometimes they are easy to confuse with SMD diodes.

It should be noted that earlier, when SMT installation was still in its infancy, capacitors in a cylindrical case were in use and were marked in the form of colored stripes. Now they are becoming less and less common.

Zener diodes and diodes are increasingly produced in plastic cases black color. The casing on the cathode side is marked with a stripe.

Schottky diode BYS10-45-E3/TR in DO-214AC package

Sometimes zener diodes or diodes are manufactured in a three-terminal SOT-23 package, which is actively used for transistors. This creates confusion when determining component ownership. Keep this in mind.

In addition to zener diodes, which have a plastic case, leadless zener diodes in cylindrical glass cases MELF and MiniMELF are quite widespread.

Zener diode 18V (DL4746A) in MELF glass case

And this is what an SMD indicator LED looks like.

The most a big problem such LEDs is that it is very difficult to desolder them from the printed circuit board with a regular soldering iron. I suspect that radio amateurs hate them fiercely for this.

Even when using a hot air soldering station, it is unlikely that you will be able to desolder an SMD LED without consequences. With little heat transparent plastic The LED melts and simply “slides” off the base.

Therefore, beginners, and even experienced ones, have a lot of questions about how to desolder an SMD LED without damaging it.

Just like other elements, microcircuits are adapted for surface mounting. Almost all popular microcircuits that were originally produced in DIP packages for through-hole mounting also have versions for SMT mounting.

To remove heat from chips in SMD cases, which heat up during operation, the printed circuit board itself and copper pads on its surface are often used. Copper pads on the board, heavily tinned with solder, are also used as a kind of radiators.

The photo shows a clear example where the SA9259 driver in the HSOP-28 package is cooled by a copper pad on the surface of the board.

Naturally, not only ordinary electronic components, but also entire functional units are sharpened for surface mounting. Take a look at the photo.

Microphone for Nokia C5-00 mobile phone

This is a digital microphone for mobile phones Nokia C5-00. Its body does not have leads, and instead of them contact pads (“nickels” or “pads”) are used.

In addition to the microphone itself, a specialized microcircuit for amplification and signal processing is also mounted in the case.

The same thing happens with microcircuits. Manufacturers are trying to get rid of even the shortest leads. Photo #1 shows the MAX5048ATT+ linear stabilizer chip in a TDFN package. Next under No. 2 is the MAX98400A chip. This is a Class D stereo amplifier from Maxim Integrated. The microcircuit is made in a 36-pin TQFN package. The central pad is used to dissipate heat to the surface of the printed circuit board.

As you can see, the microcircuits do not have pins, but only contact pads.

Number 3 is the MAX5486EUG+ chip. Stereo volume control with push-button control. Housing - TSSOP24.

IN Lately Manufacturers of electronic components are trying to get rid of pins and make them in the form of side contact pads. In many cases, the contact area is transferred under bottom part housing, where it also serves as a heat sink.

Since SMD elements have small sizes and installed on the surface of the printed circuit board, then any deformation or bending of it can damage the element or disrupt contact.

For example, multilayer ceramic capacitors (MLCC) can crack due to pressure on them during installation or due to excessive dosage of solder.

Excess solder leads to mechanical stress on the contacts. The slightest bend or impact provokes the appearance of cracks in the multilayer structure of the capacitor.

Here is one example of how excess solder on the contacts leads to cracks in the structure of the capacitor.

Photo taken from TDK's report "Common Cracking Modes in Surface Mount Multilayer Ceramic Capacitors". So, a lot of solder is not always good.

And now a little mystery to spice up our long-winded story. Look at the photo.

Determine which of the elements are shown in the photo. What do you think is hidden under the first number? Capacitor? Maybe inductance? No, it's probably some kind of special resistor...

And here is the answer:

№1 - ceramic capacitor standard size 1206;

No. 2 - NTC thermistor (thermistor) B57621-C 103-J62 at 10 kOhm (size 1206);

No. 3 - electromagnetic interference suppression choke BLM41PG600SN1L(size 1806).

Unfortunately, due to their size, the vast majority of SMD components are simply not marked. Just like in the above example, it is very easy to confuse the elements, since they are all very similar to each other.

Sometimes, this circumstance complicates the repair of electronics, especially in cases where it is impossible to find a technical documentation and a diagram.

You've probably already noticed that SMD parts are packaged in perforated tape. It, in turn, is twisted into a reel-reel. Why is this necessary?

The fact is that this tape is used for a reason. It is very convenient for feeding components into automatic mode on assembly and assembly machines (installers).

In industry, installation and soldering of SMD components is carried out using special equipment. Without going into details, the process looks like this.

Using stencils, solder paste is applied to the contact pads under the elements. For large-scale production screen printing machines (printers) are used, and for small-scale production, material dosing systems are used (dosing solder paste and glue, pouring compound, etc.). Automatic dispensers are needed for the production of products that require operating conditions.

Then the automated installation of SMD components on the board surface occurs using automatic component installation machines (installers). In some cases, parts are fixed on the surface with a drop of glue. The installation machine is equipped with a system for picking up components (from the same tape), a technical vision system for recognizing them, as well as a system for installing and positioning components on the surface of the board.

Next, the workpiece is sent to the oven, where the solder paste is melted. Depending on the technical process, reflow can be carried out by convection or infrared radiation. For example, convection reflow ovens can be used for this purpose.

Cleaning the printed circuit board from flux residues and other substances (oil, grease, dust, aggressive substances), drying. For this process, special washing systems are used.

Naturally, the production cycle uses many more different machines and devices. For example, these could be X-ray inspection systems, climate test chambers, optical inspection machines and much more. It all depends on the scale of production and the requirements for the final product.

It is worth noting that, despite the apparent simplicity of SMT technology, in reality everything is different. An example is defects that occur at all stages of production. You may have already observed some of them, for example, solder balls on the board.

They are formed due to stencil misalignment or excess solder paste.

It is also not uncommon for voids to form inside the solder joint. They may be filled with flux residues. Oddly enough, the presence of a small number of voids in the connection has a positive effect on the reliability of the contact, since the voids prevent the propagation of cracks.

Some of the defects even received established names. Here are some of them:

"Tombstone" - this is when the component “stands up” perpendicular to the board and is soldered with one lead to only one contact. Stronger surface tension from one of the ends of the component forces it to rise above the contact pad.

"Dog ears" - uneven distribution paste in the print, provided there is a sufficient amount of it. Causes solder jumpers.

"Cold soldering" - poor quality solder connection due to low soldering temperature. Appearance The solder joint has a grayish tint and a porous, lumpy surface.

Effect " Pop Corn" ("Popcorn effect") when soldering microcircuits in BGA package. A defect that occurs due to the evaporation of moisture absorbed by the microcircuit housing. When soldering, moisture evaporates, a swelling cavity is formed inside the case, which, when collapsed, forms cracks in the microcircuit case. Intense vaporization during heating also squeezes out solder from the pads, which results in uneven distribution of solder among the contact balls and the formation of bridges. This defect is detected using x-rays. Formed due to improper storage of moisture-sensitive components.

Quite important consumables in SMT technology is solder paste. Solder paste consists of a mixture of very small balls of solder and flux, which makes the soldering process easier.

Flux improves wettability by reducing surface tension. Therefore, when heated, melted solder balls easily cover the contact surface and terminals of the element, forming a solder joint. Flux also helps remove oxides from the surface and also protects it from environmental influences.

Depending on the composition of the flux in the solder paste, it can also act as an adhesive that fixes the SMD component on the board.

If you have observed the process of soldering SMD components, you may have noticed the effect of the element’s self-positioning effect. It looks very cool. Due to surface tension forces, the component seems to align itself relative to the contact surface on the board, floating in liquid solder.

This is how it would seem simple idea installation of electronic components on the surface of the printed circuit board allowed to reduce the overall dimensions electronic devices, automate production, reduce component costs (SMD components are 25-50% cheaper than conventional ones) and, therefore, make consumer electronics cheaper and more compact.

SMD components (chip components)- these are the components electronic circuit, applied to a printed circuit board (motherboard of a computer, laptop, tablet, smartphone, hard drive, etc.) using surface mounting technology - SMT technology (surface mount technology). That is, all electronic elements that are “fixed” to the board in this way are called SMD components (surface mounted device).

This type of installation is characterized by the fact that, unlike the older technology of through installation (when under electronic component: transistor, resistor, capacitor, a hole is drilled in the PCB), SMD components are located much more compactly on printed circuit board. The components themselves are much smaller.

If you pay attention to a modern laptop motherboard, you can see that it is SMD components that make up the bulk of the parts on the board - there are many of them and they are located very closely (small multi-colored squares and rectangles in gray and black colors), and on both sides of the PCB. In the following picture, the SMD components are marked in red.

The motherboard of a tablet or smartphone is made exclusively using SMT (surface mount) technology and SMD elements, since there is no space or need for through-hole mounting.

In desktop computer motherboards, both mounting technologies are used more often than others. In the figure below, through-hole installation elements are marked in green. The contacts of the components (electrolytic capacitors in this case) are inserted into special holes in the motherboard and soldered on the reverse side.

Advantages of SMD components and surface mounting

• Smaller SMD components compared to through-hole components;
• Much more high density placement on the board;
• Higher density of tracks (connections) on the PCB;
• Components can be located on both sides of the board;
• Small errors during SMT installation (soldering) are automatically corrected by the surface tension of molten tin (lead);
• Better resistance to mechanical damage due to vibration;
• Lower resistance and inductance;
• There is no need to drill holes and, as a consequence, a lower initial production cost (economic effect);
• More suitable for automated assembly. Some automatic lines are capable of placing more than 136,000 components per hour;
• Many SMD components cost less than their through-hole counterparts;
• Suitable for devices with a very low profile (height). The printed circuit board can be used in a package that is only a few millimeters thick

Flaws

• Higher requirements for production base and equipment;
• Low maintainability and higher demands on repair specialists;
• Not suitable for mounting connectors and connectors, especially when used in cases with frequent disconnections and connections;
• Not suitable for use in high power and high load applications

Using materials: Surface-mount technology,

In our turbulent age of electronics, the main advantages of an electronic product are small size, reliability, ease of installation and dismantling (disassembling equipment), low energy consumption and convenient usability ( from English- Ease of use). All these advantages are by no means possible without surface mount technology - SMT technology ( S urface M ount T echnology), and of course, without SMD components.

What are SMD components

SMD components are used in absolutely all modern electronics. SMD ( S urface M mounted D evice), which translated from English means “surface-mounted device.” In our case, the surface is a printed circuit board, without through holes for radioelements:

In this case, SMD components are not inserted into the holes of the boards. They are soldered onto contact tracks, which are located directly on the surface of the printed circuit board. The photo below shows tin-colored contact pads on a mobile phone board that previously had SMD components.

Pros of SMD components

The biggest advantage of SMD components is their small size. The photo below shows simple resistors and:

Thanks to the small dimensions of SMD components, developers have the opportunity to place large quantity components per unit area than simple output radioelements. Consequently, the installation density increases and, as a result, the dimensions of electronic devices decrease. Since the weight of an SMD component is many times lighter than the weight of the same simple output radio element, the weight of the radio equipment will also be many times lighter.

SMD components are much easier to desolder. For this we need a hairdryer. You can read how to desolder and solder SMD components in the article on how to solder SMDs correctly. It's much more difficult to seal them. In factories, special robots place them on a printed circuit board. No one solders them manually in production, except for radio amateurs and radio equipment repairmen.

Multilayer boards

Since equipment with SMD components has a very dense installation, there should be more tracks on the board. Not all tracks fit on one surface, so printed circuit boards are made multilayer. If the equipment is complex and has a lot of SMD components, then the board will have more layers. It's like a multi-layer cake made from short layers. Printed tracks, connecting the SMD components are located right inside the board and cannot be seen in any way. An example of multilayer boards is mobile phone boards, computer or laptop boards (motherboard, video card, RAM etc).

In the photo below blue board– Iphone 3g, green board – computer motherboard.

All radio equipment repairmen know that if it overheats multilayer board, then it swells into a bubble. In this case, the interlayer connections break and the board becomes unusable. Therefore, the main trump card when replacing SMD components is the correct temperature.

Some boards use both sides of the printed circuit board, and the mounting density, as you understand, doubles. This is another advantage of SMT technology. Oh yes, it’s also worth taking into account the fact that the material required for the production of SMD components is much less, and their cost during mass production of millions of pieces literally costs pennies.

Main types of SMD components

Let's look at the main SMD elements used in our modern devices. Resistors, capacitors, low-value inductors, and other components look like ordinary small rectangles, or rather, parallelepipeds))

On boards without a circuit, it is impossible to know whether it is a resistor, a capacitor, or even a coil. The Chinese mark as they please. On large SMD elements they still put a code or numbers to determine their identity and denomination. In the photo below these elements are marked in a red rectangle. Without a diagram, it is impossible to say what type of radio elements they belong to, as well as their rating.

The standard sizes of SMD components may be different. Here is a description of the standard sizes for resistors and capacitors. Here, for example, is a rectangular SMD capacitor yellow color. They are also called tantalum or simply tantalum:

And this is what SMDs look like:

There are also these types of SMD transistors:

Which have a high denomination, in SMD version they look like this:

And of course, how can we live without microcircuits in our age of microelectronics! There are many SMD types of chip packages, but I divide them mainly into two groups:

1) Microcircuits in which the pins are parallel to the printed circuit board and are located on both sides or along the perimeter.

2) Microcircuits in which the pins are located under the microcircuit itself. This is a special class of microcircuits called BGA (from English Ball grid array- an array of balls). The terminals of such microcircuits are simple solder balls of the same size.

The photo below shows a BGA chip and its reverse side, consisting of ball pins.

BGA chips are convenient for manufacturers because they save a lot of space on the printed circuit board, because there are no such balls under any BGA chip there could be thousands. This makes life much easier for manufacturers, but does not make life any easier for repairmen.

Summary

What should you use in your designs? If your hands don’t shake and you want to make a small radio bug, then the choice is obvious. But still in amateur radio designs Dimensions don’t really play a big role, and soldering massive radioelements is much easier and more convenient. Some radio amateurs use both. Every day more and more new microcircuits and SMD components are being developed. Smaller, thinner, more reliable. The future definitely belongs to microelectronics.