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SMD soldering techniques of electronic components

In Electronic Infomation Category: S | on April 13,2011

With the times and SN74LS20N datasheet and technological advances, and SN74LS20N price and now more and SN74LS20N suppliers and more use of the chip circuit board components. Chip components for its small size and easy to maintain more and more loved by everyone. But for many people, on the chip components was "fear", especially for some beginners, because they think they do not have the ability to solder components, the traditional line that it is not as easy to solder components to grasp, in fact, These concerns are totally unnecessary. Readers can use the right tools and have some knowledge of manual welding chip, chip components will soon become the welding experts.

First, the benefits of using chip components

First we to understand the benefits of chip components. Compared with the lead components, chip components has many advantages. The first: small, light weight, easy to save and post. 0805 chip resistor as commonly used in packaging or 0603 than we use many smaller line resistance. Dozens of line resistance can fill a bag with the words, but enough to replace the chip resistors installed thousands or even tens of thousands. Of course, this is not to consider the case can withstand the maximum current. Second: the chip components easier than welding and removal of line components. Chip components do not have holes, with a small tin. Line the most troublesome component is the most stressful for demolition, friends have done this experience, in two or more layers of PCB board, even if it is only two pins, removed and it is easy is not always easy damage electronic circuit boards, multi-pin to mention. The demolition of chip components much easier, not just two pins easily removed, even if one or two hundred more than the component pin can also be removed several times without damaging the circuit board. Third: the chip components and a very important benefit, that is to increase the stability and reliability of the circuit, it is to increase the production of the production rate of success.

This is because the small size chip components, and does not require vias, thus reducing the stray electric fields and stray magnetic fields, which in the high-frequency analog circuits and high-speed digital circuits is particularly important. Review said, I can bear "responsibility" to say that as long as you adapt to and accept once the chip components, except as a last resort, you may never want to use the line element of the.

Second, the welding chip components need a common tool

Chip components in the understanding of the benefits, let us understand some commonly used welding patch components required for some of the basic tools (see Figure 1).

hand soldering SMD components in Figure 1 are commonly used tools

1. Electric iron

Hand soldering components, this is definitely an essential. Here to recommend the kind of tip more pointed, because dense patches in the welding pin when the chip can be accurately convenience of a one or a few pins for welding.

2. Solder

Good solder wire welding of the patch is also very important, if conditions permit, when the chip components in the welding, the use of fine solder wire as far as possible, so easy to control to the tin, so do not waste tin solder and suck trouble.

3. Forceps The main role is to

forceps and place convenient to pick up the chip components, such as when soldering chip resistors, you can clamp the clamp resistor into the circuit board welding. Forceps tip and flat front end requirements for components in the folder. In addition, for some chips need to prevent static electricity, need to use anti-static tweezers.

4. Solder wick

Soldering SMD components, it is prone to too many conditions on the tin.

Particularly in the welding-intensive multi-pin SMD chip, the chip can easily lead to even more than the adjacent pins are solder feet short. At this point, the traditional suction tin is no good, and this time on the need to use braided solder wick.

Solder wick to sell welding equipment in place to buy, if not you can get the copper wire to replace, will be described later.

5. Rosin

Rosin is the most commonly used welding flux, because it can precipitate the oxides in the solder to protect the solder from oxidation, increasing the flow of solder. Components in the welding line, if the first component scraping rust off, put rosin on the use of iron hot, and then on the tin. Chip components in the welding, the resin in addition to the role, can also help with the welding wire can be used as a solder wick.

6. Paste

Hard on the tin in welding iron and other items, you can use solder paste, it can remove the metal surface oxide, which is corrosive.

Chip components in the welding, sometimes you can use it to "eat" solder, to solder glossy and firm.

7. Hot air gun

Hot air gun is the use of its hot air gun to blow out the core components of welding and removal of the tool. The use of the technology requirements are relatively high.

Remove or install from small components to large areas of integrated circuits can be used hot air gun. On different occasions, the temperature and wind on the amount of hot air gun and other special requirements, the temperature is too low will cause components Weld, the temperature is too high will damage the components and circuit boards. Excessive wind will be blown away small components. For ordinary patch welding, you can not to the hot air gun, described in detail in this do not do.

8. Magnifier

Some special small dense patch pin chip pin soldering need to check whether, after completion of welding normal, with or without short circuit, this time employing the eye is very laborious, so you can use a magnifying glass to convenient and reliable View the welding conditions for each pin.

9. Alcohol

In the use of rosin as a flux, it is easy to leave the extra rosin on the circuit board. For beautiful, then you can be on the board with alcohol cotton balls have left the place clean rosin 10. Other common tools required to patch welding in addition to the above-mentioned, there are some, such as sponges, plate washer water stiff brush, glue and so on. In this do to say, conditional friends can use to understand and hands-on practice.

(From left to right, first row is: hot air gun, tweezers, solder wire. The second row are: electric iron, flux, solder wick)

III chip components of the manual welding steps

Welding tools in understanding the patch after the welding step is now explained in detail.

1. Clean and fixed PCB (printed circuit board)

Welding prior to soldering the PCB should be checked to ensure that a clean (see Figure 2). Above the surface of its oily fingerprints, and oxides and the like to be removed, so as not to impact on the tin. PCB hand soldering, if conditions allow, can be welded and fixed station and the like so as to facilitate welding, in general, like the fixed hand, it is worth noting that to avoid finger contact with the pad on the PCB effect on the tin.

Figure 2 a clean PCB

2. Fixed chip components

Fixed chip components is very important. According to the pin number of chip components, and a fixed method can be divided into two - one leg and multi-pin fixation fixation. For the small number of pins (typically 2-5) of the chip components such as resistors, capacitors, diodes, transistors, etc., generally one foot fixation. That is a first pad on the board of its tin (see Figure 3).

Figure 3 for a small pin on the device should be one foot tin

Holding forceps and then left hand into the installed position and light components withstood the circuit board, the right hand has been tinned iron close to the pin pad weld molten solder (see Figure 4). To weld a pad will not move after the components are, at this time to release the forceps. As for the pin and multi-faceted distribution of multi-chip, chip, chip, fixed leg is difficult to better, then they need more foot fixed, usually on the legs can be fixed using the method (see Figure 5). That is fixed a pin and then solder the pins opposite the pin welding fixed, the chip is fixed so as to achieve good purpose. Note that the pin and intensive multi-chip-chip, precision alignment pin pad is particularly important, should be carefully checked, because the weld is good or bad decision by this premise.

Figure 4 on the fixed pin welding small components

more pins in Figure 5 feet or more legs of the components of fixed welding

Is worth emphasizing that, chip pins must be judged correctly.

, For example, sometimes we carefully fixed to the chip or welding is complete, check that pin when the corresponding error - not the first pin to pin as the first leg to weld it! A rude awakening! Therefore, the detailed preparatory work must not be careless.

3. Welded the rest of the pin After

fixed component to cope with the rest of the pin welding. For small components pin can be left hand solder, soldering iron right hand, followed by spot welding can be. For the pin and intensive multi-chip, in addition to spot welding, the welding can take drag that foot in the tin on the side of the pin and then use iron to melt the solder the remaining pins on the side of the erased (see Figure 6) , the molten solder can flow, it is sometimes the right board can also be tilted, which knocked off the excess solder. It is noteworthy that, regardless of spot welding, or drag, are likely to cause short-circuit adjacent pins are tin (see Figure 7). This is not to worry, because you can get, need to be concerned that all the pins are connected together with a good pad, no Weld.

Figure 6 on the pin more drag soldering SMD chips

Figure 7 do not worry about the pins caused by welding short

4. Remove excess solder

Mentioned in step 3 pin caused by welding short circuit, and now is how to dispose of the excess solder. In general, you can get sucked previously mentioned tin solder with siphoning off the excess. Solder wick is very simple to use, adding to the amount of flux, solder wick (such as rosin) and close to the pad, with a clean solder iron tip on the suction belt, to be solder wick is heated to be absorption pad the solder has melted, slowly from one end to the other side of the pad light pressure drag, solder Jibei inhalation zone. Should be noted that after the absorption of tin, with the suction tip should be on the tin solder wick pad also evacuated at this time if the suction pad on the tin with a stick, do not pull solder wick, but then Flux to bring Canada to the absorption or re-tin tip after heating with a solder wick to pull the pads and smooth out around the components to prevent scorch. If not sold on the market dedicated solder wick, can be used in the thin copper wire and solder wick from the system (see Figure 8). Made as follows: After the Strip the wire, exposing the inside of the thin copper wire, this time with a soldering iron melt some of rosin in the wire on it. Remove excess solder after effects shown in Figure 9. In addition, if satisfied with the results of welding, you can re-use solder wick clean solder, soldering components again.

Figure 8 with a home-made chip solder wick to absorb the excess solder pin

Figure 9 remove the excess solder on the chip pins after the renderings

5. Cleaning welding place

Welding and remove excess solder, the chip even if the welding is basically good. However, the use of rosin solder and solder wick to help suck the sake of tin, pin board around the chip some rosin residue (see Figure 9), although the work and does not affect the normal use of the chip, but not pretty. Inspection and may cause inconvenience. Because it is necessary to clean up the remnants. Clean-up methods can be used washer water, where, using the alcohol wash, cleaning tool with a cotton swab, you can clamp the tissue of the sandwiched class (see Figure 10). It should be noted when the cleaning wipe is alcohol in moderation, the higher the concentration of the best to quickly dissolve the residue of rosin and the like. Next, erase the strength to control good, not too big to avoid abrasion damage to the chip, solder layer and the pin and so on. Figure 11 the effect of washing is completed. At this point soldering iron or hot air gun can be used to scrub the location of the appropriate alcohol heated to allow rapid evaporation of residual alcohol. At this point, the chip welding is over.

Figure 10 removed with alcohol when welding residual rosin

Figure 11, cleaning with alcohol the effects of welding location map

IV Summary

Sum up, the whole soldering SMD components are fixed - Welding - clean up such a process. One component of the welding quality is the premise of fixed, must be patient, to ensure that each pin and its corresponding pad aligned precisely. Multi-pin chip in the welding, solder short on the pin is not to worry, you can use solder wick to suck welding or soldering iron used to solder only the factors after molten solder to remove the excess. Of course, is to master these skills through practice. Limited to space reasons, only the text of a multi-pin chip welding demonstration, for many other types of multi-pin SMD chip, the pin-intensive, mechanical strength, quantity, etc. are not the same in the case of the corresponding The welding method is basically the same, but slightly different details of the deal. Therefore, in order to become a master of welding chip components, we need more practice to increase proficiency. If conditions permit, if the old board like the old chips can be used more skilled.

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