Soldering methods and processes Introduction to circuit board soldering methods

Welding is one of the important links in the manufacture of electronic products, if there is no corresponding process quality assurance, any one well-designed electronic products are difficult to meet the design requirements. In the process of scientific research and development, design trial production, technological innovation in the production of one or two circuit boards, it is impossible and unnecessary to use automatic equipment, often need to be hand-loaded welding. In mass production, from the screening test of components, to the circuit board assembly welding, are completed by automated machinery, such as automatic testing machines, component cleaning machines, tin lining machines, shaping machines, insertion machines, wave soldering machines, leg cutting machines, printed circuit board cleaning machines, etc.. These computer-controlled production equipment, in the modernization of large-scale production of electronic products play an important role in helping to ensure the consistency of process conditions and welding operations, improve product quality.

Welding classification and soldering conditions

Welding classification

Welding technology in the electronics industry is very wide range of applications in the electronics manufacturing process, almost all kinds of welding methods are used, but the most common, the most representative is the tin soldering process. Universal, the most representative of the tin soldering method. Tin soldering is a kind of welding, it is the solder and the melting point than the solder low solder *** with the heating to the tin soldering temperature, in the case of the solder does not melt, solder melting and infiltration of the weld surface, relying on the diffusion of the two atoms to form a connection of the weldment. Its main features are the following three points:

1? Solder melting point is lower than the weldment;

(2)? Solder and solder *** with the solder heated to tin soldering temperature, the solder melts and the solder does not melt;

(3)? The formation of welding relies on the molten state of the solder to infiltrate the welding surface, by capillary action to make the solder into the gap of the weldment, the formation of an alloy layer, so as to realize the bonding of the weldment.

In addition to containing a large number of chromium, aluminum and other elements of some alloy materials should not be soldered with tin welding, most other metal materials can be soldered with tin welding. Tin soldering method is simple, only need to use simple tools (such as soldering iron) can be completed welding, soldering repair, component removal and replacement, re-welding and other processes. In addition, tin soldering also has the advantages of low cost, easy to realize the advantages of automation, in electronic engineering technology, it is the earliest, most widely used, accounting for the largest proportion of the welding method.

Basic skills of manual soldering iron welding

Using the soldering iron for manual soldering, it is not difficult to master, but there are certain technical essentials. People who have long been engaged in the production of electronic products is to improve the quality of soldering from four aspects: materials, tools, methods, operators.

The most important of these is, of course, human skills. After a considerable period of welding practice and experience, understanding, can not grasp the technical aspects of welding; even if the welding work is engaged in a longer period of time, skilled workers, but also can not guarantee that the quality of each welded joints are completely consistent. Only a full understanding of the principles of welding coupled with attentive practice, it is possible to learn the basic skills of welding in a relatively short period of time. Some of the specific methods and points of attention described below, are the summary of practical experience, is a beginner to quickly master the welding skills of the shortcut.

Beginners should be practiced diligently, and constantly improve the operation of the skills, can not save the quality of welding problems to the whole machine circuit debugging time to solve.

Correct posture of welding operation

Mastering the correct posture of the operation can ensure the physical and mental health of the operator and reduce labor injuries. In order to reduce the flux heating volatile chemical substances on the person's harm, reduce the inhalation of harmful gases, in general, the soldering iron to the nose distance should be no less than 20cm, usually to 30cm is appropriate.

Virtual welding causes and its harm

Virtual welding is mainly caused by the oxides and dirt on the surface of the metal to be welded, it makes the solder joints become a connection state with contact resistance, resulting in the circuit does not work properly, there is a connection between the unstable phenomenon of sometimes good and sometimes bad, the noise increases without regularity, to the debugging of circuits, the use of the circuit and maintenance of a major hidden trouble. In addition, there is also a part of the virtual solder joints in the circuit began to work for a long period of time, to maintain contact is still good, so it is not easy to find. But in the temperature, humidity and vibration and other environmental conditions, the contact surface is gradually oxidized, the contact slowly become incomplete. The contact resistance of the virtual solder joints will cause local heating, local temperature rise and promote incomplete contact with the solder joints further deterioration of the situation, and ultimately even make the solder joints fall off, the circuit can not work properly. This process can sometimes be up to one or two years, the principle can be explained by the "primary battery" concept: when the solder joints moisture so that water vapor penetrates the gap, water molecules dissolve metal oxides and dirt to form an electrolyte, false solder joints on both sides of the copper and lead-tin solder equivalent to the two electrodes of the primary battery, lead-tin solder to lose electrons to be oxidized, the copper to get the electrons are reduced. In such a primary battery structure, metal loss corrosion occurs in the virtual solder joints, the local temperature rise exacerbates the chemical reaction, and mechanical vibration allows the gap to expand until the vicious circle of the virtual solder joints to eventually form a circuit breaker.

According to statistics, nearly half of all electronic product failures are caused by poor soldering. However, from an electronic device with thousands of solder joints, to find out the cause of the failure of the solder joints to the virtual soldering is really not an easy thing. Therefore, false soldering is a major risk to circuit reliability and must be strictly avoided. Manual soldering operations, especially to pay attention to.

Generally speaking, the main causes of soldering is: poor quality of solder; flux reduction of poor or insufficient dosage; the surface of the welded place is not pre-cleaned, tin is not secure; soldering iron head temperature is too high or too low, the surface of the oxidized layer; soldering time is not a good grasp of the too long or too short; welding in the welding of the solder has not yet solidified, the welded components are loose.

Power check

At the end of the appearance of the check that the connection is correct, before the power check, which is the key to test the performance of the circuit. If you do not go through the strict appearance check, power check is not only more difficult, but also may damage the equipment and instruments, resulting in safety accidents. For example, the power supply connection line welding, then power on the equipment will be found to add power, of course, can not check.

The power-on inspection can find many minor defects, such as bridging of electrical circuits that cannot be observed visually, but it is not easy to detect the hidden danger of internal soldering. So the fundamental problem is still to improve the skill level of the welding operation, can not leave the welding problem to the inspection process to complete.

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