What is the manual immersion welding process specification (tin furnace)?

1 Purpose of welding procedure specification:

Effectively control the welding process, make it technologically advanced, economical, reasonable, safe and applicable, and ensure the quality.

2. Production equipment and raw materials? ：

Solder oven, clamp, scraper, circuit board with components inserted, flux, tin bar, diagonal pliers. ?

3. prepare?

Open the soldering furnace, set the temperature to 240-265 degrees (high in winter and low in summer), and when the temperature is stable (add appropriate tin bars if necessary). ?

4, operation method:

(1), clamp the circuit board with the right hand, visually check whether the components meet the requirements, and correct them with the left hand.

(2) Clamp the inserted circuit board with a clamp, spray a little flux on the copper surface, and scrape off the oxide layer on the tin surface of the tin furnace with a scraper.

(3) Immerse the copper surface of the circuit board sprayed with flux at an oblique angle of 15. When the circuit board is in contact with the tin liquid, slowly push the circuit board forward to make the circuit board vertical to the liquid surface. The circuit board is immersed in 0.5mm, and the tin immersion time is 2-5 seconds (depending on the pin thickness of components, the thicker the pin, the longer and the shorter the time). ?

(4) After tin dipping, lift it slowly and gently at an oblique angle of15, keep it steady, and do not shake it, so as to prevent virtual welding and fullness. ?

(5) When it is basically cured after 5 seconds, observe whether the circuit board is inclined and deformed, and put it into the next process after passing the test. ?

(6) After using the operating equipment, turn off the power.

5. What are the key points of manual welding?

The following points are derived from the welding mechanism and proved to be universally applicable by practical experience. ?

(1), master the heating time.

When welding, we can use different heating rates, such as the shape of the welding head is not good, and when welding large weldments with a small soldering iron, we need to extend the time to meet the requirements of solder temperature.

In most cases, extending the heating time is harmful to the assembly of electronic products, because:

A, the bonding layer of solder joint exceeds the appropriate thickness due to long-term heating, which leads to the deterioration of solder joint performance. ?

B, printed boards, plastics and other materials will be deformed and deteriorated if heated too much. ?

C. after heating, the performance of components changes or even fails. ?

D, solder joint surface due to flux volatilization, loss of protection and oxidation. ?

Conclusion: The shorter the time, the better, on the premise of ensuring solder wetting the weldment. ?

(2), keep the appropriate temperature:

If we use high-temperature soldering iron to weld solder joints in order to shorten the heating time, it will bring another problem: the flux in solder wire does not have enough time.

Welding surface overflow and premature volatilization failure; The fast melting speed of solder affects the function of flux; Because the temperature is too high, although the heating time is short, it also causes overheating. ?

Conclusion: In order to keep the welding head in a reasonable temperature range, the general experience is that the welding head temperature is 50℃ higher than the melting temperature of solder.

The ideal state is to shorten the heating time at a lower temperature. Although this is contradictory, we can get a satisfactory solution through operation in practice. ?

(3) It is harmful to apply force to the solder joint with the welding head.

The welding head mainly transfers heat to the solder joint by increasing the contact area, and it is futile to apply force to the solder joint with a soldering iron.

In many cases, it will cause damage to the welded parts. For example, the welding points of potentiometers, switches and connectors are often fixed on plastic components, and the result of force is easy to cause the original failure. ?

6, soldering operation essentials?

(1), weldment surface treatment?

The weldments encountered in manual soldering iron welding are all kinds of electronic parts and wires. Unless the electronic components within the "warranty period" are used in mass production, the surface of the weldment often needs to be cleaned to remove rust, oil stain, dust and other impurities that affect the welding quality. Manual operation often uses mechanical scraping and alcohol and acetone scrubbing. ?

(2) Pre-welding?

Pre-welding refers to wetting the lead or conductive welding part of the component to be welded with solder in advance, which is also commonly known as tin plating, tin plating and tin lining.

It is accurate to call it pre-welding, because its technological mechanism is the whole process of welding-solder wets the surface of the weldment, and forms a bonding layer through metal diffusion, so that the surface of the weldment is "plated" with a layer of solder. ?

Pre-welding is not an essential operation for welding, but it is almost essential for manual soldering iron welding, especially for maintenance, debugging and development. ?

(3) Don't use excessive flux?

Appropriate flux is essential, but don't think that the more the better.

Too much rosin not only causes a heavy workload of cleaning around the solder joint after welding, but also prolongs the heating time (rosin needs to be melted and volatilized to take away heat), which reduces the working efficiency; However, when the heating time is insufficient, it is easy to mix with solder to form the defect of "slag inclusion"; For the welding of switching elements, too much flux tends to flow to the contacts, resulting in poor contact. ?

The appropriate welding dose should be that rosin water can only wet the solder joint to be formed, and it cannot flow through the printed board to the component surface or socket hole (such as IC socket).

For the welding wire with rosin core, there is basically no need to apply flux. ?

(4) Keep the welding head clean?

Because the welding head is in a high temperature state for a long time during welding, it is in contact with substances decomposed by heat, such as flux, and its surface is easily oxidized to form a layer of black impurities, almost forming a heat insulation layer, which makes the welding head lose its heating effect.

So always wipe off the impurities on the soldering iron frame. It is also a common method to wipe the welding head with a wet cloth or sponge at any time. ?

(5), heating by solder bridge?

In non-assembly line operation, there are many shapes of solder joints welded at one time, so it is impossible for us to change the welding head often.

In order to improve the heating efficiency of the welding head, it is necessary to form a solder bridge for heat transfer.

The so-called solder bridge is to reserve a small amount of solder on the soldering iron as a bridge for heat transfer between the welding head and the weldment when heating. ?

Obviously, because the thermal conductivity of molten metal is much higher than that of air, the weldment is quickly heated to the welding temperature. It should be noted that the tin reserve as a solder bridge should not be too much. ?

(6) Is the amount of solder appropriate?

Too much solder not only consumes more expensive tin unnecessarily, but also increases the welding time and reduces the working speed accordingly.

More seriously, in high-density circuits, excessive tin can easily cause imperceptible short circuits. ?

But too little solder can't form a firm bond, which reduces the strength of solder joints, especially when welding wires on the board. Insufficient solder often causes wires to fall off. ?

(7), weldments should be strong?

Do not move or vibrate the weldment before the solder solidifies, especially when clamping the weldment with tweezers, be sure to wait until the solder solidifies before taking out the tweezers.

This is because the solidification process of solder is a crystallization process. According to the crystallization theory, the external force (the movement of the weldment) in the crystallization process will change the crystallization conditions and produce coarse crystals, which is called "cold welding".

Appearance phenomenon is dull surface and bean dregs; The internal structure of solder joint is loose, and air gap and crack are easy to appear, which leads to the decrease of solder joint strength and poor conductivity.

Therefore, before the solder solidifies, the weldment must remain still, and various suitable methods can be used to fix the weldment or reliable clamping measures can be adopted in actual operation. ?

(8) What should I pay attention to when the soldering iron is evacuated?

The soldering iron should be handled in time, and the angle and direction of evacuation have a certain relationship with the formation of solder joints. ?

When the soldering iron is removed, a slight rotation can keep the proper solder in the solder joint, which needs to be realized in actual operation.

Extended data:

1, technical points of soldering?

As an operation technique, manual soldering can only be mastered through practical training, but following the basic principles, learning from the accumulated experience of predecessors and using the correct methods can get twice the result with half the effort.

2. What are the basic conditions for soldering?

(1), weldability of weldments?

Not all materials can be connected by welding. Only some metals with good weldability (strictly speaking, they should be weldable) can be connected by soldering.

Generally, copper and its alloys, such as gold, silver, zinc and nickel, have good weldability, while aluminum, stainless steel and cast iron have poor weldability, so special flux and method are generally needed for welding. ?

(2) Is the solder qualified?

Lead-tin solder whose composition is not up to standard or whose impurities exceed the standard will affect the quality of solder, especially some impurities, such as zinc, aluminum and cadmium. Even the content of 0.00 1% will obviously affect the wettability and fluidity of solder and reduce the welding quality.

Obviously, no matter how clever a chef is, it is impossible to process delicious food with inferior raw materials. ?

(3) Is the flux suitable?

Different fluxes should be used to weld different materials. Even for the same material, when different welding processes are used, such as manual soldering iron welding and immersion welding, different fluxes are often used, and different fluxes are also needed for post-welding cleaning and no-cleaning.

For manual welding, rosin and active rosin can meet the assembly requirements of most electronic products.

It should also be pointed out that the amount of flux must also be paid attention to, too much or too little is not conducive to tin welding. ?

(4) Is the solder joint design reasonable?

Reasonable geometry of solder joints is very important to ensure the quality of solder joints.

reference data

Baidu encyclopedia-immersion welding