What Is Manual Welding?

Manual soldering is the foundation of tin-lead soldering technology. Although modern companies have generally used the production process of automatic insertion and automatic welding, product trial production, production of small batch products, production of products with special requirements and high reliability (such as the manufacture of rockets in satellite technology, satellite manufacturing, etc.), etc. It also uses manual welding. Even if miniaturized and mass-produced products such as printed circuit board structures use automatic soldering, there are still a certain number of solder joints that need to be soldered by hand, so there is currently no soldering method that can completely replace manual soldering. Therefore, in the process of training high-quality electronic technicians and electronic operators, the manual welding process is an essential training content. ^[1]

Manual soldering is a basic operation skill in the assembly of electronic products. It is suitable for product trial production, small batch production of electronic products, debugging and maintenance of electronic products, and some occasions that are not suitable for automatic soldering. It is a welding process that uses a soldering iron to heat the metal piece to be soldered and the tin-lead solder. The molten solder wets the heated metal surface to form an alloy. After the solder solidifies, it connects the metal pieces to be welded, so it is also called Soldering. ^[2]

1. Select a suitable solder, and use a low melting point solder wire for electronic components.

2. Flux, use 25% rosin in 75% alcohol (weight ratio) as flux.

3. The electric soldering iron should be tinned before use. The specific method is: heat the electric soldering iron, just after the solder can be melted, apply flux, and then apply the solder to the soldering iron evenly, so that the soldering iron can be eaten evenly. A layer of tin.

4, soldering method, the pads and component pins are cleaned with fine sandpaper, and coated with flux. Use a soldering iron tip to pick up an appropriate amount of solder and touch the solder joint. After the solder on the solder joint has melted and immersed the component lead, the soldering iron tip is gently lifted up along the component pin to leave the solder joint.

5. The welding time should not be too long, otherwise it is easy to burn the components. If necessary, the pins can be clamped with tweezers to help heat dissipation.

6, the solder joints should be in the shape of a sine wave, the surface should be bright and smooth, no tin thorn, moderate tin volume.

7. After soldering is completed, the residual flux on the circuit board should be cleaned with alcohol to prevent the carbonized flux from affecting the normal operation of the circuit.

8. The integrated circuit should be soldered last. The soldering iron should be reliably grounded, or the residual heat should be used after power off. Or use an integrated circuit socket, solder the socket and plug in the integrated circuit.

9. The electric soldering iron should be placed on the frame of the soldering iron.

Contact welding is performed when a heated tip or ring directly contacts the solder joint. A tip or ring is mounted on the welding tool. The welding tip is used to heat a single welding point, and the welding ring is used to heat multiple welding points at the same time. There are various design structures for single-nozzle welding tools and welding tips.

There are also various design structures for soldering tips in the form of soldering iron rings. Discrete rings with two or four sides are mainly used for component removal. Rings are designed primarily for multi-pin components such as integrated circuits; however, they can also be used to remove rectangular and cylindrical components. A soldering iron ring is very useful for removing glued components. After the solder is melted, the soldering iron ring can twist the component to break the glue connection.

Four-sided components, such as plastic pin chip carriers, pose a problem because it is difficult for the soldering iron ring to touch all the pins at the same time. If the soldering iron ring does not touch all the pins, no heat conduction occurs, which means that some solder joints do not melt. Especially on J-pin components, all pins may not be on the same reference plane, which makes it impossible for the soldering iron ring to touch all the pins at the same time. This situation can be catastrophic, as the pads still soldered to the pins will be pulled from the PCB when the operator removes the component.

Weld tips and rings require frequent preventive maintenance. They need to be cleaned and sometimes tinned. It may require frequent replacement, especially when using a small soldering iron tip.

Contact welding systems can be categorized from low to high prices, often limiting or controlling temperature. The choice depends on the application. For example, surface mount applications typically require less heat than through-hole applications.

1. Constant temperature system, providing continuous and constant output, continuously transmitting heat. For surface mount applications, these systems should operate in the temperature range of 335 ~ 365 ° C.

2. The temperature limiting system has the temperature limiting ability to help keep the temperature of the system in an optimal range. These systems transfer heat discontinuously, which prevents overheating, but heating recovery may be slow. This may cause the operator to set a higher temperature than desired and speed up the welding. The operating temperature range for surface mount applications is 285 ~ 315 ° C.

3. Control the temperature system and provide high output capability. These systems, like temperature limiting systems, transfer heat discontinuously. Response timing and temperature control are superior to temperature limiting systems. The operating temperature range for surface mount applications is 285 ~ 315 ° C. These systems also provide better deviation capability, typically 10 ° C.

Features related to contact welding systems include: In most cases, contact welding is the easiest and lowest cost method of repair welding and component removal and replacement. The glued component can be easily removed with a solder ring. contact

Hot air welding is accomplished by using a nozzle to direct heated air or an inert gas, such as nitrogen, to the solder joints and pins. Hot air equipment options range from simple handheld units to heating a single location to complex automatic unit designs to heat multiple locations. The handheld system removes and replaces rectangular, cylindrical and other small components. Automatic systems take off and replace complex components, such as dense feet and area alignment components.

The hot air system avoids the local thermal stresses that can occur with contact welding systems, which makes it the first choice in applications where uniform heating is critical. The hot air temperature range is generally 300 ~ 400 . The time required to melt the solder depends on the amount of hot air. Larger components may require more than 60 seconds of heating before they can be removed or replaced. Nozzle design is important; the nozzle must direct hot air toward the solder joint, sometimes avoiding the component body. Nozzles can be complex and expensive. Adequate preventive maintenance is necessary; nozzles must be cleaned and stored regularly to prevent damage.

Related characteristics of hot air systems include: The low efficiency of hot air as a heat transfer medium, reducing thermal shock due to slow heating rates. This is an advantage for certain components, such as ceramic capacitors. Using hot air as a heat transfer medium eliminates the need for direct iron tip contact. Temperature and heating rates are controllable, repeatable and predictable. Issues related to hot air systems include: Hot air welding equipment prices range from medium to high. Automated systems are quite complex and require high-tech operations.

Flux can be dropped in vials, and sealed or refillable flux pens can be used. Often, operators use too much flux. I would prefer to use flux pens because they limit the amount of flux used. I would also prefer to use solder with a flux core, which contains flux and solder alloys. When using solder with a flux core and liquid flux, ensure that the fluxes are compatible with each other.

Surface mount soldering usually requires smaller diameter tin wires, typically in the range of 0.50 ~ 0.75mm. Through-hole welding usually requires a larger diameter tin wire, ranging from 1.20 to 1.50 mm.

Solder paste can also be dripped with a syringe, although many manual soldering methods heat the solder paste too quickly, causing splashing and solder balls. Flux glue, rather than solder paste, is very useful for replacing area-aligned components.