Once you're ready, the next step is to start the actual welding.

The first step is the soldering of the pins of the components, which is the first step in the complete manual soldering process.

That is, the soldered objects such as the pins of the components, solder lugs, and pads are respectively pre-evaporated with a soldering iron to coat a layer of solder, so that no false soldering can be basically guaranteed.

In the soldering operation, we must develop a good habit of tin the components in advance: for those surface oxidation, stained pins and insulating paint of the wire, the surface must also be cleaned before tinning, manual soldering - the general use of scraping method treatment, scraping must pay attention to be comprehensive, uniform, especially when dealing with those small diameter wires, can not leave scars at the beginning of scraping.

Because it is impossible to carry out such a complicated manual operation during mass production, the welding quality depends entirely on the weldability of the components to ensure it, and the weldability test of the components must be done before production.

After the soldering of the pins of the components, the complete soldering will begin.

First of all, the circuit board is tilted towards the operator, the working surface of the soldering iron tip is leaned against the pins and pads of the soldered part, and the welding wire is sent to the soldering iron head at the intersection of the three to melt, and the molten solder will flow to and fill the gap between them immediately, so that the heat is quickly conducted, and the solder will be heated up soon.

Since the solder wire has a flux core, the melted rosin flux will flow to the surface of each metal in the soldering area, playing various roles as flux.

Subsequently, when the temperature rises to a certain level, diffusion occurs, and the solder infiltrates the surface of the solder, and solder joints begin to form.

Then, move the soldering iron, the solder joint is completed, the soldering iron is evacuated, the soldering iron is cooled and solidified, etc., but due to the limited solder dose in the solder wire, if the solderability of the solder object is not very good, often the solder has already been evaporated before the solder joint is fully formed, so that the solder surface is oxidized and discolored, and the solder can not be continued to be soldered.

In order to get fresh flux, it is necessary to send another section of solder wire to the "person" to let the flux in the solder wire flow out and replenish, and this makes the total amount of solder droplets too large and the excess solder must be shaken off from under the solder joint with a soldering iron.

Sometimes, when you encounter a solder joint that is difficult to solder, you have to send the "human" wire again and again, and then shake off the excess solder until the actual solder joint is formed.

In order to improve the utilization rate of solder wire and shorten the soldering time as much as possible, the soldering wire that starts to be delivered to people can be divided into two parts.

First of all, a part is directly sent to the soldering iron tip to fill the gap, increase the contact surface of the soldering iron's heat transfer, start the whole soldering process, and when the weldment is warmed up, it will lose no time in turning to the opposite side of the soldering iron, and directly send another part of the solder wire to the component pins and pads.

In this way, the solder wire acts as a guide to the formation of solder joints. This eliminates the need to move back and forth on both sides of the soldering iron, and allows the metal on the opposite side to be coated with flux as soon as possible to avoid oxidation caused by heating up.

The operation essentials are still to always operate with the flux liquid film, so that the solder is always in a shining state before solidifying.

Because the solder droplets become matte, it means that the surface layer has been oxidized, it is no longer metal, and it will not melt at the soldering temperature.

The basic requirement of the two welding methods is the same, that is, to obtain a true solder joint with a perfect alloy layer in the shortest possible time. In practice, the second technique is often mixed with the first technique.

After welding, it is impossible to end it like this, and the quality of the welding must be inspected.

There are many ways to inspect the quality of welding, and the more advanced method is to use an instrument. Huaxing Electronics Factory and Xunyang Electronics Factory definitely do not have this condition at present, so they have to use the method of observing the appearance and re-soldering with a soldering iron to inspect.

First of all, the appearance observation method, the most important thing about the welding quality of a solder joint is to see whether it is virtual welding, followed by the appearance. However, an experienced person can judge the quality of the internal soldering of the solder joint by its appearance.

The surface of a good solder joint should be smooth and bright, and there should be no pulling, wrinkling, bubbles, slag inclusions, pitting, etc.; The transition from the solder to the metal to be welded should be a smooth and smooth wet-like concave surface.

For example, on a chip component, in addition to the profile of excellent solder joints, the rest are various bad solder joints, and the problems of these solder joints are described below.

The appearance of the solder joints looks smooth and full, but when you look closely, you can find that the contact angle between the solder and the pad and pin is greater than 90 degrees, then it indicates that the solder has not infiltrated them, and such a solder joint must be a virtual solder.

If the appearance of the solder joint is not smooth, and there is the phenomenon of wire drawing and tailing, then it indicates that the flux is not used enough in the welding process, at least in the later stage of welding is the end in the absence of flux, and such a solder joint is difficult to ensure that it is not a virtual solder.

Other defects such as continuous welding, lack of welding, etc. are quite obvious defects and will not be repeated.

It is best to use a 3-5 times magnifying glass when checking the quality of the solder joint by the observation method, under the magnifying glass, you can clearly observe the details of the contact between the solder on the surface of the solder joint and the soldered object, and here is the key to judging the quality of the solder joint.

If you want to resolder with a soldering iron, we will introduce the rosin rewelding test method.

The most reliable way to test the authenticity of a solder joint is to re-solder, re-melt the solder joint with a soldering iron full of rosin flux and lack of solder, and remove the soldering iron from the side or below.

Rewelding with rosin is the most reliable inspection method, and at the same time, it can also accumulate experience and improve the accuracy of inspection of solder joints by observation method.

The above two are to check the virtual welding, in addition to the virtual welding, there are some welding defects should also be avoided, the insulation layer of the lead wire is stripped too long, so that the wire has the danger of colliding with other solder joints, the temperature is too high and the time is too long, the substrate material is carbonized, bubbling, the pad has been stripped from the board base, the components are lost fixed, and the circuit connected with the pad will be torn off.

After the quality inspection of the welding, the welding is almost done. Why do you say it's done, because many times, excess rosin will affect the aesthetics.

So, the next thing is to deal with it! You can use plate washing water, or high-purity industrial alcohol to wash off the remaining rosin, Huaxing Electronics Factory and Xunyang Electronics Factory are washed with 99.7% industrial alcohol when welding, you can wash these rosins without a trace, and finally, the complete welding is done!

The above welding is currently Huaxing Electronics Factory and Xunyang Electronics Factory can do, in Fu Xin's mind, there is also a kind of welding, which is a relatively high-end welding, dip welding.

In the mass production of electronic products, a large number of soldering work of most components on the circuit board must be completed by one-time integral soldering. The overall soldering of the circuit board includes dip soldering, wave soldering and various reflow soldering for SMD, where dip soldering is a semi-manual and semi-mechanical method, and the main equipment for dip soldering is dip soldering furnace and foaming rosin burner.

The tin furnace is equipped with an automatic temperature control device, most of which are equipped with a timing relay for the cycle cycle of 24 hours to 7 days, which can automatically open and stop the furnace according to the set program, with a power of 120 to 2500 watts, a working temperature of 100 to 300 degrees, and a maximum temperature of more than 400 degrees.

The hand-dipping foaming rosin burner is used to foam the flux into a foam inrush so that the flux can be evenly applied to the solder surface of the circuit board and maintain this state without dripping before dipping. The dip oven should be equipped with good ventilation equipment above the furnace in order to completely remove the smoke generated during welding.

The furnace temperature of dip soldering should be carefully adjusted, and it should be set according to different solders and different workpieces. Dip soldering is performed with a large stainless steel clip about 250 mm long, with the right shape and elasticity to clamp the two long sides of the circuit board.

Before entering the furnace for immersion welding, you should check whether the inserted parts are skewed, jumping out and other phenomena, and if so, they should be sorted out slightly; Then use cardboard to scrape off a layer of tin oxide film on the surface of the molten tin, and then dip the circuit board dipped in flux.

In dip soldering, the technique of dipping forward is adopted, and at the same time, the direction of continuous soldering on the circuit board is perpendicular to the direction of movement.

The front end is slightly tilted down when immersed and slightly upturned during welding, making it a slightly arc-shaped action with the best effect. Because the circuit board will bend upwards at the moment of heating, taking such an action can make the soldering time of each part of the solder joint the same, which is conducive to reducing virtual soldering and continuous soldering.

The depth of the solder liquid level on the circuit board is measured so that the solder will not run to the component surface.

The residence time of the circuit board in the tin liquid is about two seconds, and the specific time should be varied according to the different workpieces, furnace temperature and solder flux performance, so as to accurately grasp the components with the least soldering defects and no heat damage.

The composition of the solder in the immersion furnace will change with continuous use: the composition of tin will decrease, the proportion of lead will increase, that is, the so-called "segregation phenomenon", and the concentration of harmful impurities such as copper and zinc will also rise.

The welded workpiece should be separated by cardboard and placed in layers, so as to avoid splashing tin beads on the bottom plate during welding, and debris falling into the parts when colliding with each other, forming excess objects that are not easy to clean.

When operating, you must wear protective equipment such as masks, pay attention to the safety and fire prevention of flammable materials such as fluxes and thinners, and clean up the flux scabs by the tin furnace in time.

……

Maybe Xiao Hei felt that Fu Xin still had doubts, so he simply said: "It is estimated that it is soldered, and the design of the SMD components is not fixed, this is the most difficult, for a while, I can't do it alone." ”

Fu Xin had no choice but to smile bitterly, it seems that he is still too anxious, science and technology have not yet developed to this extent, there is no basis, it is really difficult to do it out of thin air, just like he did in his previous life to engage in scientific research, he did it for a few years, and in the end it turned out to be nothing. (To be continued.) )