Wave soldering is an electronic manufacturing process that is widely used in the assembly of printed circuit boards (PCBS). It achieves welding between component pins and PCB pads by passing the PCB through a stable, liquid solder crest with a certain height at a certain speed. Wave soldering technology has become the first choice for mass production of electronic products because of its high efficiency and high degree of automation. However, in order to ensure the quality of the welding, the temperature control during the wave soldering process is crucial.

This article will explore in depth how to correctly set the temperature of wave soldering, including understanding the working principle of wave soldering, the effect of temperature on welding quality, and the factors to consider when setting the temperature. This not only helps to improve the quality of welding, but also extends the life of the equipment and reduces energy consumption, thus bringing economic benefits to the manufacturer.

Working principle of wave soldering

Before going into detail about how to set the wave soldering temperature, we need to understand the basic working principle of wave soldering. Wave soldering system is usually composed of preheating zone, spray flux zone, wave crest zone and cooling zone. Each area has its own specific function:

Preheating zone

Preheating is a very important step in wave soldering process. Its purpose is to make the PCB and the components on it reach an appropriate temperature in order to facilitate the subsequent welding process. Preheating reduces thermal shock, prevents component damage, and helps remove moisture or solvents, avoiding the formation of bursts or bubbles.

Spray flux area

At this stage, the flux is evenly sprayed onto the PCB. The role of the flux is to remove oxides and other contaminants from the surface of the metal, promote a good bond between the solder and the metal, while protecting the unwelded part from high temperatures.

Crest zone

This is the core part of wave soldering. After being preheated and coated with flux, the PCB passes through a crest formed by the molten solder. When the PCB contacts the wave crest, the solder will flow into the gap between the component pin and the pad under the action of gravity and surface tension, forming a firm welding point.

Cooling zone

After welding is completed, the PCB enters the cooling zone, where the solder joint is quickly cured by natural cooling or forced cooling (such as fan blowing) to ensure the stability and strength of the welded structure.

Effect of temperature on welding quality

In the process of wave soldering, improper temperature setting may lead to various welding defects, which will affect product quality. Here are some common problems and their causes:

Cold welding

If the temperature is too low, the solder cannot flow sufficiently to fill all the places that need to be welded, which will lead to poor welding, known as “cold welding”. Cold welding is not only unreliable, but also may cause poor electrical contact, and the final product may have potential trouble.

Virtual welding/fake welding

When the temperature is not high enough, the solder can not completely wet the metal surface, so that the solder joint looks normal but in fact does not have a good electrical connection, which is virtual welding or false welding. In this case, the solder joint is easy to break, which may lead to circuit failure after long-term use.

Thermal injury

If the temperature is too high, it may burn sensitive components, especially those small integrated circuits (ics) that are sensitive to temperature. In addition, high temperature may also cause physical damage such as PCB deformation and delamination.

Solder ball

Too high a temperature or too long a time can also lead to excessive flow of solder, forming unnecessary solder balls. These solder balls may short-circuit adjacent pads, causing circuit failure.

Flux residue

Improper temperature Settings can also affect the activity of the flux, resulting in excessive flux residue. This makes cleaning difficult and may corrode the board.

Factors to be considered in setting wave soldering temperature

In order to find the most suitable temperature setting for wave soldering, a number of factors must be considered, and the following are some key points:

Component type

Different types of components have different temperature resistance characteristics. For example, passive components such as ceramic capacitors and resistors can generally withstand higher temperatures, while active devices such as transistors, diodes and especially microprocessors are more sensitive. Therefore, when designing the welding process, priority should be given to the maximum temperature limit that the most vulnerable components can withstand.

Solder alloy composition

Common solder alloys have different melting point ranges. For example, a conventional Sn63Pb37 (63:37 tin to lead ratio) solder has a melting point of about 183°C, while a lead-free solder such as SAC305 (tin silver copper) has a melting point of about 217°C. Choosing the right solder alloy is crucial to determining the correct welding temperature.

PCB material

PCB substrates also have their own thermal stability requirements. FR-4 is one of the most common PCB substrates, and its glass conversion temperature (Tg) is usually around 130-140°C. This means that during the heating process, the PCB should not exceed this temperature too much to avoid warping or other structural changes.

Welding time

Welding time refers to the residence time of the PCB in the wave crest. Longer time means higher accumulated heat, which will also adversely affect components and PCBS. Therefore, in addition to adjusting the temperature, it is also necessary to optimize the welding time to ensure the quality of the solder joint while protecting other components.

Environmental condition

Environmental factors such as humidity and ventilation in the workshop will also indirectly affect the welding effect. For example, working in a high humidity environment, the steam generated by water evaporation may affect the quality of the welding interface; Good ventilation can help eliminate harmful gases and improve the working environment.

Best practices in practice

According to the above theoretical knowledge, we can take the following measures in practice to accurately set the wave soldering temperature:

1. Develop detailed process documents

Each batch of product should have a clear wave soldering process document, including the recommended preheating temperature, peak temperature, welding time and cooling rate parameters. These data should be based on the specific product design, components used, solder type, and PCB material characteristics.

2. Use temperature monitoring devices

The installation of online temperature monitoring system can track the temperature change during the wave soldering process in real time to ensure that the actual operation conforms to the predetermined process specifications. Modern wave welders are often equipped with advanced sensors and control systems that automatically adjust the temperature to maintain stability.

3. Test welding and testing

Before the formal production, it is recommended to conduct a small batch test welding and a comprehensive inspection of the sample. The quality of solder joints can be evaluated by visual inspection, X-ray inspection, shear force testing, etc. Adjust the temperature setting according to the test welding results until the desired welding effect is obtained.

4. Regular maintenance and calibration

Wave soldering equipment needs regular maintenance, including cleaning the nozzle, replacing the filter, checking the heating element and so on. In addition, the temperature sensor also needs to be calibrated regularly to ensure measurement accuracy. This is the only way to ensure consistent and high quality results from each weld.

5. Train operators

Train operators to be familiar with the operation and safety procedures of wave soldering equipment. They should know how to set the temperature correctly, identify anomalies, and take corrective action accordingly. Skilled operation skills can not only improve production efficiency, but also reduce quality problems caused by misoperation.

conclusion

To sum up, the correct setting of wave soldering temperature is the key to guarantee welding quality and improve production efficiency. Through the understanding of the working principle of wave soldering, the understanding of the influence of temperature on welding quality, and taking into account the interaction of many factors in the actual operation, we can work out a scientific and reasonable wave soldering temperature management program. I hope the information provided in this article can help you better master this technology and contribute to the development of the electronic product manufacturing industry.