How to Solder a SMD Resistor with a Soldering Iron

How to desolder a microcircuit

The need to dismantle radio elements arises in several cases:

• Dismantling the faulty element;
• Incorrect installation of the radio component;
• Soldering from the donor board due to the lack of a new microcircuit.

In all these cases, except for the first, the main conditions are maintaining the integrity and working condition of the soldered part and the integrity of the printed circuit board.

Dismantled microcircuits

To carry out this work, it is necessary to observe accuracy and simple rules that were developed back when most of the range of radio components was in short supply. The urgent question was how to remove an expensive microcircuit from the board without damaging it.

Chip types

The wide variety of microcircuit packages has led to the fact that soldering techniques began to differ. Previously, the most widespread were microcircuits with pin pins for mounting into holes on a printed circuit board. Subsequently, with an increase in the degree of integration and the widespread use of automated soldering lines, surface mount elements with flat or ball leads began to be used.

ICs (integrated circuits) with solder pins are typically DIP and SIP packages with two and one row of pins, respectively.

Surface mounting ( SMD ) allows installation of ICs with pins of the following types:

• Flat leads brought outside the housing - SOIC, SOP, QFP (square housing);
• Flat legs, bent inward, under the body - SOJ, PLCC, QFJ;
• Ball terminals - BGA.

Each variety has several subspecies. The total number of housing types is in the dozens.

Safe work with semiconductor radio components

Before you unsolder a part from the board with a soldering iron, you need to know the following. Semiconductor elements are extremely sensitive to overheating. Also, tracks on a printed circuit board at high temperatures or when the soldering time is exceeded can peel off from the substrate or break, which is even worse.

Temperature conditions

Soldering station - operating principle and types

The temperature of the soldering iron tip should be 200-250⁰С. At higher temperatures, peeling of the printed tracks and overheating of the microcircuit may occur. The same goals are set for the soldering time of one leg - no more than 3 seconds.

Note! Some sites advise for dismantling to focus not on the temperature, but on the power of the soldering iron. It is not right. Their temperatures are the same, it’s just that a less powerful one may not be able to cope with melting the solder at the pin due to intense heat removal, and a too powerful one can easily overheat the pins and the board. The best option is a 40 W soldering iron.

Many microcircuits are sensitive to static electricity. It is necessary to work with an electrostatic wrist strap on and a grounded tool.

Electrostatic bracelet

Board design

DIY soldering station

Printed circuit boards differ in the number of printed layers and the method of installing radio components:

• Single layer;
• Double layer;
• Multilayer;
• For DIP elements;
• For SMD components.

One board can contain both DIP and SMD elements on one or both sides. Multilayer printed circuit boards, in addition to outer layers, have internal ones, which usually serve for general shielding or wiring of power circuits. Thus, the motherboards of modern computers or mobile phones have up to seven layers.

Multilayer PCB

Dismantling techniques

The method of soldering microcircuits depends mainly on the type of pins, although there are universal methods.

Dismantling the microcircuit with a soldering iron

How to test a zener diode with a multimeter

This is the most time-consuming and unreliable method. It is used only when the number of microcircuit legs is minimal. Before soldering microcircuits with a soldering iron, the tip of the tip is carefully tinned and cleaned of solder residues so that it remains only in the form of a thin film. The molten solder that surrounds the IC leg is transferred to the tip under the action of tension. By repeating the procedure several times, the leads are completely released.

Important! Before each touch of the board, the tip is cleared of solder. The touch time should not be more than three seconds. If the leg is not completely freed, you can only work on it after some time has cooled down. At this time, you can make the following conclusions.

Removing the chip using a razor blade

When working with planar elements, an ordinary razor blade will come to the rescue. For convenience, the razor blade is broken in half lengthwise. Leaning the blade close to the border of the terminal and the board, heat the scion until it melts. By inserting a blade between the leg and the board, they are separated. The blade is made of stainless steel, so solder does not stick to it.

Using dismantling braid

The special dismantling braid works thanks to the capillary effect, drawing in the molten material. You can use braided shielded cable with the same effect. The braid must be clean, without traces of oxidation. In order to improve the spreading of the melt, the braid is moistened with liquid flux.

Dismantling microcircuits using a desoldering pump

The desalination pump is a special piston that, when moving, draws in the melt, releasing the outlet. This method is suitable for working with DIP and SIP components.

Desoldering pump

Using medical needles

This method has proven to work best when dismantling ICs, especially for single-sided printed material. Double sided PCB can also be used to remove needles from syringes. When choosing a needle, you need to ensure that its inner diameter allows the leg of the microcircuit to fit freely, and its outer diameter allows it to fit into the hole on the printed circuit board. The tip of the needle is ground with a file until a smooth surface is obtained.

The needle is placed on the tip of the leg and the terminal is heated with a soldering iron. After the solder has melted, the needle is inserted into the hole of the board and smoothly rotated around the axis until the tin solidifies. After this, the needle is removed from the stem, which is now completely free. The needle material (stainless steel) is not tinned, so rotation around the stem is only necessary to make it easier to remove it from the hole.

Use of alloy rose

Using a rose alloy, you can desolder all the terminals of the IC at the same time, due to the fact that the low-melting alloy spreads between the terminals and evenly and simultaneously transfers heat to all of them from the heated soldering iron tip. After complete heating, the part is carefully removed from the board using tweezers.

This method has one disadvantage - after dismantling, it will not be possible to collect the remaining rose alloy, since it will be clogged with excess tin and lead, which will change its composition and melting point.

How to desolder a microcircuit from a board with a hairdryer

When working with SOJ, PLCC, QFJ and BGA packages, a soldering station or hair dryer with temperature control is required. Using the station, the entire section of the board is heated until the microcircuit is released, and using a hair dryer with a nozzle, a stream of hot air is directed to the terminals of the IC until they are released.

Radioelements must be desoldered at a temperature of 250⁰C. To prevent overheating, adjacent elements should be covered with aluminum foil.

How to remove capacitors from a motherboard

To desolder capacitors or other two-terminal elements, there is no need to use a special soldering tool. During the dismantling process, one of the terminals of the capacitor is heated, while simultaneously tilting the element so that the leg comes out of the hole. Next, repeat the same with the second leg, tilting the part in the opposite direction. To avoid tearing, do not press hard on the capacitor. By warming up both terminals in turn, they are gradually released.

Source: https://amperof.ru/sovety-elektrika/kak-vypayat-mikrosxemu.html

Soldering technologies for SMD components and their implementation at home

Over the past few years, surface mount radio technology has become very popular and is used in the production of most modern electronic devices.

The abbreviation SMD stands for surface mounted device, which in turn can be translated as “surface mounted device”.

Actually, the very name of this technology fully reveals its essence - radio components are mounted directly on the surface of the board, but unlike wall-mounted components, SMD components do not require special holes for mounting.

The absence of special holes for installing radio components made it possible to make printed circuit boards more compact. The use of surface mount technology can significantly save space on the board, which in turn allows you to increase the density of radio components and make more complex devices.

In addition, most SMD components are miniature in size, due to the fact that they do not require large pins like lead components. But many people mistakenly believe that all SMD components, without exception, are very small. Among them, quite often there are large radio components that differ from their “lead” counterparts only in the type of conclusions (which is logical).

But let's move on to the essence of the article, namely the question of how soldering of SMD components is carried out and whether it can be done at home.

SMD and regular electric soldering iron

Quite often, in small-scale production or the production of device prototypes, specialists use conventional electric soldering irons. How to solder SMD components using a contact soldering iron?

1. First, flux is applied to the place where the component is to be installed.

2. Next, the component itself is installed, which needs to be soldered.

3. Apply a little solder to the soldering iron tip. The main thing is not to overdo it and not to apply too much.

4. A drop of solder is applied to the contacts of the component. Thanks to the flux, the solder spreads well and securely bonds the component to the contact on the board.

If there is too much solder, the soldering area will be sloppy. Excess solder can be easily lulled with a special tape, or simply with the tip of a soldering iron.

To solder SMD components with a regular soldering iron, it is better to replace the standard tip with a thin one. If this is not the case, you can use the standard one, but before starting serious work you will need a little training.

The advantages of this method are its simplicity. If you have a regular soldering iron, then nothing else is needed besides it. The disadvantages are also obvious - the operating speed will be quite low (especially if you do not have SMD soldering skills).

Soldering using a hot air soldering station (hair dryer)

This method is also often used in small-scale production and repair. At the same time, the quality of soldering will be much higher than when using a conventional soldering iron. Soldering with a hot air soldering station or hair dryer occurs as follows:

1. Special solder paste is applied to the board.

2. An SMD component is installed that needs to be soldered.

3. The component and soldering area are heated with a hairdryer. At the same time, the flux evaporates from the solder paste, and the smallest grains of solder melt and spread, soldering the component to the board contacts.

The advantages of this method are a neat place for soldering the component to the board and the simplicity of the entire process. The main thing is not to apply too much paste. In this case, it is not always necessary to apply an additional portion of flux, since it is already contained in the paste.

There is only one disadvantage of this method - a hot-air soldering station can be quite expensive. Also, the air flow does not act pointwise, but on a specific area. If you do not install a nozzle for working with miniature SMD components, there is a high probability of heating and melting the solder on already soldered components.

Soldering with an infrared soldering station

Implementing this type of soldering at home can be difficult since the entire process is carried out using an infrared soldering station. As the name implies, the flux is heated using infrared radiation. In this case, it is important to control the heating temperature, and you cannot do without heating the board itself. This is necessary to prevent it from deforming when heated with an infrared soldering iron.

There are many types of infrared soldering stations, among which you can find both amateur and professional ones, designed for work in small-scale production and in service centers. The only drawback of such soldering stations is their high cost, compared to even good hot-air stations.

How does the soldering process take place using such equipment?

1. First, solder paste is applied to the board.

2. Next, install the components that need to be soldered.

3. The component, together with the soldering site, is heated by infrared radiation, as a result of which the component is reliably soldered to the soldering site.

There are complex, programmable soldering stations that are capable of independently soldering elements onto the board. You just need to apply paste and components to the soldering areas, and the soldering station will do the rest. At the same time, you can monitor the process from the monitor screen, tracking the progress of work and temperature indicators.

The advantages of this method are obvious - with a good soldering station, the board production process can be made semi-automatic. At the same time, the quality of the work performed will always be at its best. But there are also some disadvantages - a soldering station is quite expensive, and using semi-automatic stations requires certain skills and knowledge.

Some craftsmen assemble their own soldering stations. Their cost is much lower than factory ones, but the assembly and programming process itself is quite complex.

Soldering in an induction furnace

This process is used in industrial production of printed circuit boards. It allows you to produce tens or even hundreds of printed circuit boards per hour, while the entire process can be fully automated. How does the induction soldering process and preparation for it occur?

1. A special stencil is applied to the board.

2. Through a stencil, a layer of solder paste is applied to the board.

3. Next, components are installed on the board.

4. The board is sent to an induction furnace, where the entire soldering process takes place.

The advantages of induction soldering are high production speed and the ability to fully automate the process. Disadvantages - such mini-production is difficult to implement at home. And for the most part it is not profitable either.

So what's the bottom line?

Despite the complexity of some soldering methods, all of them can be implemented at home:

• Soldering with a regular electric soldering iron is the most affordable way to install SMD components. With a little practice you will be able to solder even complex components with a large number of pins.
• Soldering with a hot air soldering station provides optimal soldering quality and will not cause any particular difficulties even for beginners, but such a station is much more expensive than a regular soldering iron. But if you are a true radio amateur and often work with SMD components, such costs will be justified.
• The infrared soldering station provides excellent soldering quality. If a branded station is beyond your means, you can try to assemble your own, on your own. There are many hobbyist projects that even have lists of all the required components, and you can also download open source firmware. But remember that assembling your own soldering station requires certain skills and knowledge.
• Induction soldering is the most difficult, as it requires knowledge, skills and rare components. Nevertheless, all this can be implemented at home, but think about whether it’s worth it and whether you need to produce device boards on an industrial scale.

You might be interested in this:

Source: http://meandr.org/archives/26111

How to solder SMD elements manually

Every day, radio amateurs are increasingly using SMD parts and components in their work. Despite their size, they are easier to work with: you don’t need to drill holes in the board, bite off long pins, etc. It is imperative to master the soldering of SMD parts, as it will definitely come in handy.

This master class is not intended for beginners in soldering, but rather for amateurs who are good at soldering but have a little difficulty soldering multi-legged microcircuits or controllers.

Will need

This is a minimal set, without expensive soldering stations, hair dryers and desoldering pumps.

We solder SMD parts with our own hands

So, let's start with the most difficult thing - soldering the controller in the QFP100 case. With chip resistors and capacitors, I think everything is clear. The main rule here: there is no such thing as too much flux, or you won’t ruin the soldering with flux. Excessive application of flux prevents tin from spreading abundantly over the contacts and shorting them. There is also a second minor rule: even a little solder can be a lot. In general, you need to dose and apply it to the sting very carefully so as not to overdo it, otherwise it will flood everything at once.

Tinning the site

Experienced electronics technicians don't always perform this step, but I recommend doing it in the first couple of days.

You need to tin the board, namely the place where the controller will be soldered. Of course, the site is most likely tinned, especially if the board was made in production. But over time, an oxide film appears on the contacts, which can hinder you.

Heat the soldering iron to operating temperature. Lubricate the area generously with flux. We apply a little solder to the tip and tin the tracks.

We remove excess solder using the PSH wire. It absorbs solder perfectly due to the capillarity effect.

Installing and aligning the controller

Once the site is prepared, it's time to install the controller. There is a trick here; most solders install the microcircuit and use tweezers to align its contacts along the tracks. But this is very difficult to do, since even a slight twitch of the hand throws the controller a considerable distance.

It will be much easier to do this if you grease the corners diagonally with flux paste.

Now we install the controller and adjust it with tweezers.

As soon as the microcircuit is installed, we solder the contacts diagonally.

We check that all contacts are in the right place.

Soldering microcircuit contacts

Here you can already use both liquid and viscous flux. We apply it very liberally to the contacts.

We wet the tip with a drop of solder. We clean off excess with a sponge.

And, carefully move along the lubricated contacts.

There's no need to rush.

Removing excess flux and solder

After soldering all the contacts, it's time to remove excess solder. Probably several contacts stuck together.

We wet the contacts very generously with liquid flux. We completely clean the soldering iron tip from solder with a sponge and go over the sticky contacts. Excess solder should be drawn onto the tip.

To remove excess flux, use SBS - an alcohol-gasoline mixture mixed 1:1.

We wet it generously.

And we wipe it.

Watch the video

Be sure to watch the video, where you can clearly see the movement of the soldering iron and all the manipulations.

Source: https://labuda.blog/125715

Learning how to safely desolder radio components from boards

When some equipment breaks down, it is not at all necessary to immediately throw it in the trash. If you are interested in electronics and radio engineering, it would be wiser to solder the working elements of the microcircuit. Suddenly, in the future you will need a capacitor, transistor or resistor if you decide to make a homemade electronic product. In this article we will tell you how to desolder radio components from the board so as not to damage anything.

What do you need for this?

There are many devices for soldering parts. Of course, a radio amateur cannot do without a soldering iron, which will be the main assistant in this matter. However, in addition to the soldering iron, in order to desolder the element, you will need:

1. Tweezers. To remove heated radio components. Instead of tweezers, you can use an alligator clip (shown in the photo below). The advantage of the clamp is that it will securely grip the part and also become a good heat sink.
2. Hollow needles for dismantling. Buying them will not be a problem, the cost is low. Using needles, you can desolder a radio component quickly and accurately, which we will discuss below.
3. Dismantling braid. It serves as a so-called sponge that absorbs molten solder into itself, thereby cleaning the board.
4. Destination pump. The name speaks for itself. An indispensable item for frequent desoldering of radio components from boards at home.

You also need to prepare your workplace. It should be with good lighting. It is best if the lamp is located above the workplace so that the light falls vertically without creating shadows.

How to safely remove a transistor, microcircuit, diode from a board

When repairing household appliances, a home mechanic is often faced with the need to replace electronic components located on circuit boards or mounted using a hinged method.

In this case, you must work carefully, otherwise you can damage the semiconductor layer, burn out the tracks, or even destroy the case.

In order to solder a transistor, microcircuit or diode, you need to know and follow certain installation rules. Read them in this article.

Old models

A properly selected soldering iron can ensure normal heating of the contact tracks of boards and semiconductor leads.

The old EPSI model of the “Moment” type with a power of 65 watts has a universal design. It is not difficult to make it with your own hands.

Previously, resistive type models with a heating element made of thin nichrome wire were widely used.

Modern soldering irons

For specific soldering conditions, you can now purchase various types of models equipped with all sorts of functions.

For example, a soldering iron with tin suction has been specially designed for soldering microcircuits, transistors and diodes.

It quickly heats up a layer of solidified solder and easily removes it in a liquid state from the contact pad.

Radio component holders

When heating the transistor leg for tinning and soldering, you should always remove the heat from the body and semiconductor layer with some metal object.

For this purpose, tweezers or alligator clips are usually used. However, it is most convenient to work with a medical instrument with thin legs, which surgeons use during operations.

Fixing electronic boards

Radio components and boards are usually small in size and require reliable fixation in space. Soldering them while hanging is dangerous: a small wrong movement can damage the entire structure.

When working with them, one hand is already occupied: it contains a soldering iron. And the second one needs to perform some additional actions. In this case, factory or homemade vices, holders, and clamps come to the rescue. They must be used.

Soldering needles

At the moment the solder melts, they are inserted inside the board sleeve to separate the leg of the radio component from the contact track.

A home craftsman can buy a ready-made kit in a store, for example, via the Internet in China or your city.

Medical syringe needles are well suited for the same purposes. Their tips need to be sharpened to a right angle.

Molten Tin Removal Tool

There are several ways to remove liquid solder from the melt site:

• shaking onto the floor, table or other surface;
• sweeping with a brush or brush;
• suction;
• absorption into a special braid.

The first two methods are extreme; they are used in extreme cases. For normal high-quality work, the last two methods are suitable.

Liquid tin suction method

The tool adapted for it is called a tin pump. The appearance and design of one of the many models is shown in the picture.

Before work, the spring is cocked. When the solder is melted to a liquid state, the tip of the device is applied to it and by pressing a button, the force of the released spring is forced to move the piston to provide a vacuum, which draws the liquid metal into a special cavity.

Dismantling braid

It is made by weaving soft copper wire. Working with it is quite simple: a piece of braid is placed on the molten solder, and it quickly absorbs liquid tin.

Dismantling braid is sold in construction stores. An alternative can be a shielding core from an old coaxial cable for televisions, produced back in Soviet times. It is impregnated with a flux of alcohol and rosin.

Soldering conditions

When creating a workplace, you should pay special attention to its lighting. You cannot solder a radio component in semi-darkness. If your vision does not allow you to clearly see all the details, then you need to wear corrective glasses.

The electronic board must be clearly fixed in space, and the body must be in a stable position. It is best to work sitting or standing on both legs, holding the soldering iron confidently. After all, any wrong move will cause irreparable harm.

Technology for dismantling radio components

The tip of the soldering iron should be precisely placed on the layer of solder located in the socket of one leg of the transistor and quickly melt it.

Then a needle is inserted into this place from the reverse side and the tin is separated from the stem. If there is a dismantling braid or desoldering pump, then use them.

When the design of a radio component allows the use of a metal clamp to remove heat from the housing, then it must be used.

If the space for installing the soldering iron tip is very limited, then they work without using a heat remover.

In this case, special attention is paid to the length of time the radio component remains at elevated temperatures.

Features of dismantling microcircuits

The arrangement of the legs of the microcircuit strictly in a row allows you to melt the solder in all the sleeves of the contact pads of the board on one side of the case. This is a rather risky method, but in most cases with good skills it ends in success.

It is used when the tools described above for removing molten tin are not at hand, and the work needs to be done quickly.

Such operations are well provided by a transformer soldering iron with a tip made of copper wire, which can be bent to the shape of the legs of the microcircuit.

An awl or a thin screwdriver blade is placed under the microcircuit body. They act as a lever, move, and gradually pull out all the legs from their sockets at once at the moment the tin melts, but not before.

You should not try to completely remove the microcircuit in one go; it is enough to pull it out a little bit by bit on each side. At the same time, they monitor the temperature of the case and allow it to cool.

Using a similar method, I managed to remove the K554CA3 chip from the old board to work as a comparator in a homemade twilight switch.

In old boards, the legs of radio components were often bent on the reverse side and soldered. They are more difficult to dismantle. You will have to melt the tin on each leg, put a needle on the bend and use it to align the contact wire so that it comes out normally through the sleeve hole.

I suggest you watch the video by the owner of Radioblogful “How to desolder a microcircuit in three different ways”

To resolve any questions, use the ability to comment on the article. Now you can share it with your friends via social networks.

Source: https://HouseDiz.ru/kak-bezopasno-vypayat-tranzistor-mikrosxemu-diod-iz-platy/

Hand soldering of miniature SMD elements | Homemade catalog

Surface-mount components, as their name suggests, involve mounting onto the surface of the board rather than into holes like older components. SMDs (surface mount elements) are lighter, cheaper, smaller, and can be placed closer together. These factors, as well as others, have contributed to the widespread use of leadless components today.

There are many relatively inexpensive tools and simple methods for soldering and desoldering SMDs.

SMD Soldering Tools

1. Temperature-adjustable soldering iron. A 10 bucks tool with no temperature control is not really the best tool to learn how to solder SMT. You don't need an expensive soldering station, but you do need to be able to control the temperature.

A relatively inexpensive $50 adjustable soldering iron has a temperature control knob from 0 to 5.

It comes with the familiar ST3 wedge-shaped tip, which may be too wide for chip components, but it is still quite commonly used for soldering. Many people will feel more comfortable working with ST7 or ST8 tapered blades. Miniwave nozzle ST5 is convenient for soldering parts in QFP, QFN, PLCC, SOIC packages.

A small depression in its cut surface allows you to hold solder in an amount sufficient for distribution over the entire row of pins of the microcircuit.

1. Solder. For hand soldering of surface mount components, we need 60/40 tin-lead alloy in the form of a wire with a diameter of 0.015 inches (0.4 mm). There may be more lead in the alloy and thicker wire may be needed if you need to secure the connector to the board.

1. Soldering tape. This is one of the things that is simply indispensable for hand soldering. Also known as a solder scraper - helps remove solder. It is woven from thin copper wires into a long braid, and sometimes has flux inside.

1. Tweezers. Flat-tip grippers are essential for moving and holding miniature chip components. These ones with curved ends are very convenient. You can get these for about $5.

Some people use vacuum tweezers to pick up and replace small components.

1. Flux. It's not always used when manually soldering SMD boards, but some people can't do without it. Flux can be used even with ready-made solder wires, since the thinner the wire, the less solvent it contains. During soldering, the element legs heat up more than once, so it is important to add a little external flux.

1. Magnifying glass with flashlight. In any case, you will need a lot of light and a magnifying glass when soldering miniature elements. There are good head lenses like OptiVisors, which magnify 2.5 times, and have built-in lighting lamps.

To check your work you will need a magnifying glass with 10x magnification. These magnifiers are also available with a built-in flashlight.

Tape desoldering technique

To make the desoldering, place a copper pigtail on the legs of the element and run a hot soldering iron over it. The heat and flux will draw the tin onto it. Use the other end of the braid if nothing seems to be working (a small piece of it is cut off from the spool).

Depending on the circumstances, the pigtail needs to be raised higher, and the heat will be removed along it upward from the area where the soldering iron touches.

To clean the braid, you need to add more flux.

Soldering two-pin elements

Components such as resistors and capacitors often crack due to uneven heating. Solder their two opposite ends at the same time. Use tweezers to hold the part on the board. Apply a little solder to one side to create a neat fillet between the end of the element and the pad. Ideally, you should end up with a smooth bridge, and not a huge ball of tin at the end.

If not, use copper braid to remove excess solder.

Soldering SOIC and other multi-pin ICs

Use tweezers or a suction cup to hold the SOIC (Small Output Integrated Circuit) on the board. Solder one of the pins of the microcircuit, preferably it is the power pin. Then grab the other power terminal on the opposite side. Make sure all the other legs line up above their pads.

Connect the remaining legs - starting with the outermost, unsoldered contacts, apply a wave of solder, feeding tin wire to the soldering iron tip if necessary. Do this operation as quickly as possible without allowing the chip to overheat.

Removing sagging

When you are finished soldering, inspect the legs of the chip elements. Small bridges between them can be easily removed by quickly heating them with a soldering iron dipped in flux. Thick jumpers are removed in a familiar way - using soldering tape.

Source: https://volt-index.ru/electronika-dlya-nachinayushih/ruchnaya-payka-miniatyurnyih-elementov-smd.html

How to check a resistor with a multimeter without desoldering

Resistor ® is a passive element of electrical circuits that limits the voltage or current in a certain section of the circuit due to its resistance. Resistors are the most common parts in electrical and electronics. Many novice radio amateurs are wondering how to test a resistor with a multimeter. To determine the resistance value, digital and dial multimeters, or testers, are used.

Determination using a multimeter

Before measuring the resistor, it is necessary to visually determine its integrity: inspect it for burnt outer coating - paint or varnish, and also check the inscriptions on the body, if they are visible. You can determine the denomination using tables of rows or color codes , after which you can measure the resistance using a multimeter.

For testing, you can use a simple measuring device, for example, DT-830B. First of all, you need to set the measurement switch to the minimum resistance test mode - 200 Ohms, and then connect the probes to each other. The device indicator with the probes connected should show the minimum value R, which tends to zero, for example, 0.03 Ohm. After the so-called calibration, you can begin measurements.

Checking the resistance on the board

Elements with an ohmic resistance of up to 200 Ohms must be tested in this measurement range. If the instrument readings indicate infinity, it is necessary to increase the measured range with a switch from 200 Ohms to 2000 Ohms (2 kOhms) and higher, depending on the rating being tested. Before checking a resistor with a multimeter without desoldering it, you need to:

• turn off the power source;
• unsolder one pin R, since due to the mixed connection of elements in the circuit there may be differences between the nominal value of the element and the readings of its actual value in the overall circuit during measurement;
• make a measurement.

Only low-resistance resistances can be ringed on the board, ranging from one ohm to tens of ohms. Starting from 100 Ohms and above, it becomes difficult to measure them, since the circuit may use radioelements that have a lower resistance than the resistor itself.

In addition to fixed resistors, there are the following types of elements:

• variable (rheostat);
• tuning;
• thermistor or negative temperature coefficient thermistor;
• posistor with positive temperature coefficient;
• The varistor changes its values ​​depending on the voltage applied to it;
• the photoresistor changes its values ​​depending on the light flux directed at it.

Source: https://pochini.guru/sovety-mastera/kak-proverit-rezistor

How to desolder a microcircuit from a board with a soldering iron?

Hi all! The author of the blog popayaem.ru, Vladimir Vasiliev, is in touch with you. Today we will talk about various methods of dismantling microcircuits. It is with them that difficulties arise when soldering into parts of various equipment.

“Why is it needed, you can buy it anyway, it costs a penny!” the average person will exclaim, not understanding and not attaching importance to the wealth hidden in old electronic equipment. I once wrote an article about how I got hold of radio parts when I had nowhere to buy them or nothing to buy them with.

Usually, there are no problems when soldering various small things. This is not a tricky thing, I heated it from the mounting side and pulled the leads out of the mounting holes one by one. The situation is much more complicated with microcircuits; there is more than one output; while one output has warmed up, the other has already cooled down. Moreover, bending the legs one at a time is not the case; that’s the only way they will fall off.

There are several methods for dismantling microcircuits:

 Dismantling the microcircuit with a soldering iron

This is the most homeless and hemorrhagic trick when you have nothing but a soldering iron but need to desolder the microcircuit.

In order for this matter to go more or less smoothly, we clean the soldering iron from adhering solder. You can clean it with a special cellulose sponge or just with a damp cloth. Then, using a brush, coat all soldering joints with liquid flux; for this I use alcohol rosin.

Now we first stick the cleaned soldering iron tip into the rosin and then poke it into the soldering points of the microcircuit pins. As a result, slowly, bit by bit, the solder begins to transfer from the mounting pad to the soldering iron tip.

We, as it were, tin the soldering iron tip, but only take the solder from the terminals of the desired microcircuit.

So you need to do a large number of iterations, not forgetting to clean the soldering iron tip each time, until the microcircuit is released from the mounting captivity. It is very important here not to get carried away and not overheat the microcircuit. Also, mounting nickels and tracks can fly off due to overheating, but this is important in the sense that you don’t really need the microcircuit itself, but you do need the board itself.

Dismantling microcircuits using a desoldering pump

What do you think will happen if you combine an enema and soldering? You will get something shown in the figure. This is a tin pump and this construct was described in an old magazine, either “Modeler-Constructor” or “Radio Magazine”, I don’t remember.

Now they can look completely different, they can be like in the picture, they can be a modified syringe. But this does not change their essence: the soldering iron heats up the junction and the enema bulb or syringe draws out all the solder.

In principle, a very effective dismantling method.