Processing and steps before soldering iron soldering

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Soldering iron welding pre-treatment and welding steps (welding method of electric soldering iron)

(1) Pre-weld processing steps

Before soldering, the soldering parts of the component pins or circuit boards should be processed. Generally, there are three steps of “scraping”, “plating” and “measuring”:

"Scraping": It is to clean the welding parts before welding. The commonly used tools are small knives and fine sandpaper. The pins of the integrated circuit and the printed circuit board are cleaned to remove the dirt on the integrated circuit. Also need to apply flux to the components to be removed.

"Plating": It is tin plating on the scraped parts. The specific method is to apply the rosin rosin alcohol solution on the welded parts of the scraped parts, and then press the hot iron tip with tin on it and rotate the element. The device is evenly plated with a very thin layer of tin.

"Measurement": It is to use a multimeter to check whether all tin-plated components are of reliable quality. If there are components with unreliable or damaged quality, replace them with the same specifications.

(2) Welding steps

After the pre-weld treatment, the formal welding can be carried out.

Different soldering objects, the required soldering iron working temperature is also different. When judging the temperature of the soldering iron, the soldering iron can touch the rosin. If there is a "beep" sound, the temperature is suitable; if there is no sound, only If the rosin is melted barely, the temperature is too low; if the tip of the iron touches the rosin, it will smoke a lot, indicating that the temperature is too high.

In general, there are three main steps in the soldering process:

(1) First melt a small amount of solder and rosin on the soldering iron tip, and align the soldering iron and solder wire at the solder joint.

(2) When the flux on the soldering iron tip has not evaporated, the soldering iron tip and the solder wire are simultaneously contacted with the solder joint to start melting the solder.

(3) When the solder infiltrates the entire solder joint, remove the soldering iron tip and solder wire at the same time.

The soldering process is generally 2~3s. When soldering integrated circuits, the amount of solder and flux should be strictly controlled. In order to avoid damage to the integrated circuit due to poor soldering iron insulation or internal heaters inducing voltage on the housing, the application is often used. 2. The power plug of the electric iron is hot welded.

Electric soldering iron welding and prevention method thereof

When welding, it should be ensured that each solder joint is welded firmly and in good contact. The tin point should be bright, smooth and burr-free, and the amount of tin is moderate. The tin and the soldered material are fused firmly, and there should be no solder joint. The so-called virtual solder is the solder joint. Only a small amount of tin is welded, resulting in poor contact, when the time is broken. To avoid the false welding, the following points should be noted:

(1) Ensure that the metal surface is clean

If there is rust, dirt or oxide on the surface of the weldment and solder joints, it should be scraped with a knife or sandpaper before soldering until the bright metal is exposed to tin the surface of the weldment or solder joint.

(2) Master the temperature

In order to make the temperature appropriate, you should select the appropriate electric soldering iron according to the size of the component, and pay attention to the heating time. If you use a small soldering iron to solder large components or solder the ground wire on the metal substrate, it is easy to form a virtual solder.

When the soldering iron head is pressed with solder to the soldering station, if the soldering iron is removed, the solder is not left or left very little, indicating that the heating time is too short, the temperature is not enough, or the solder is too dirty; Before the soldering iron, the solder flows down, indicating that the heating time is too long and the temperature is too high.

(3) Appropriate amount of tin

According to the size of the required solder joints, the amount of tin drawn by the soldering iron is determined, so that the solder is enough to wrap the soldered material to form a solder joint with appropriate size and smoothness. If the tin is not enough, it can be replenished, but it needs to be after the tin is melted, the soldering iron is removed.

(4) Select the appropriate flux

The role of the flux is to improve the fluidity of the solder, prevent oxidation of the soldered surface, and play a role in soldering and protection. When soldering electronic components, solder paste should be avoided as much as possible. A better flux is a rosin alcohol solution. When soldering, Drop a little on the welded part.

Reflow soldering process

The reflow oven must be able to provide sufficient heat (temperature) for the entire assembly and all pin locations. Many profiled/via devices are higher and have a larger heat capacity than other SMCs assembled on the assembly. For THR applications, Forced convection systems are generally considered to be superior to IR. Separate top and bottom heating controls also help to reduce ΔT on PCB components. For computer motherboards with high stacking 25-pin DSUB connectors (1.5 in), the component body temperature is too high to Accept. The solution to this problem is to increase the bottom temperature and lower the top temperature. The time above the liquidus should be long enough to allow the flux to evaporate from the PTH, which may be longer than the standard temperature profile. The cross-section analysis may be very It is important to confirm the correctness of the reflow profile. In addition, the peak temperature and thermal gradient on the component must be carefully measured and strictly controlled. Therefore, care must be taken when setting the reflow soldering temperature profile:

Control the generation of voids/bubbles;

Monitor the temperature distribution on the board, the temperature difference between the components;

Consider the thermal compatibility of the component body;

Heating rate, time above liquid phase, peak temperature of reflow and cooling rate is.

Appropriate stable heating rate is required, because in the process, the solder paste is heated and the viscosity is lowered, and the flux is volatilized to increase the viscosity of the solder paste. The proper stable heating rate keeps the solder paste viscosity stable. It is very important to leave solder paste on the top of the pin.

Welding precautions

In addition to the soldering essentials, the soldering of printed circuit boards should also pay attention to the following points:

(1) The soldering iron is selected from the internal heat type (20 ~ 35W) or the temperature adjustment type (the temperature of the soldering iron does not exceed 300 ° C), and the tip of the soldering iron is small conical.

(2) When heating, try to make the soldering iron tip contact the copper foil and component leads on the printed board. For larger pads (more than 5mm in diameter), move the soldering iron at the moment of soldering, that is, the soldering iron rotates around the pad.

(3) For the soldering of metallized holes, not only the solder should be wetted by the solder, but also the holes should be wetted and filled. Therefore, the heating time of the metallized holes should be longer than that of the single panel.

(4) Do not use soldering iron to rub the soldering pad when soldering. It is necessary to rely on surface cleaning and pre-welding to enhance solder wetting performance. Components with poor heat resistance should use tools to assist heat dissipation, such as tweezers.

When soldering the transistor, be careful not to solder the soldering time of each tube for more than 10 seconds, and use a needle-nosed pliers or tweezers to pin the pins to prevent heat from damaging the transistor. When soldering the CMOS circuit, if the leads are short-circuited beforehand, soldering Do not remove the short-circuit line before use. For the use of high-voltage soldering iron, it is best to unplug the plug during welding and use residual heat to weld. When soldering the integrated circuit, under the premise of ensuring the infiltration, try to shorten the welding time. More than 2 seconds.

Welding method

The five-step welding method is a common basic welding method suitable for welding workpieces with large heat capacity, as shown in Figure 14.

(1) Preparing for welding

Prepare the solder wire and soldering iron and prepare for soldering.

(2) Heating weldment

Touch the soldering iron to the solder joint. Be careful to keep the soldering iron heating parts (such as the leads and pads on the printed board) heated, and then pay attention to the flat part (larger part) of the soldering iron head to contact the solder with larger heat capacity. The side or edge portion of the tip is in contact with the weldment with a smaller heat capacity to keep the weldment evenly heated.

(3) Melting solder

After the weldment is heated to a temperature at which the solder can be melted, the wire is placed at the solder joint and the solder begins to melt and wet the solder joint.

(4) Remove the solder

After melting a certain amount of solder, remove the solder wire.

(5) Remove the soldering iron

Remove the soldering iron after the solder has completely wetted the solder joint. Note that the direction of the soldering iron should be approximately 45°.

For workpieces with low heat capacity, it can be simplified to a two-step operation: prepare the solder, put the soldering iron and solder wire, remove the solder wire and remove the soldering iron.

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