Importance of wave soldering flux spraying process

Analysis of the Influence of Wave Soldering Process Spray Uniformity

In the electronics manufacturing industry, wave soldering is a critical process step, and the uniformity of flux spraying directly determines the soldering quality of electronic products, holding significant importance. To systematically investigate the key factors affecting spray uniformity, this study designed and conducted a series of experiments, aiming to provide a theoretical basis and practical guidance for the optimization of the wave soldering process.

In the specialized tests focusing on the influence of flow rate and air pressure on spray uniformity, the industry-recognized fax paper test method was employed to evaluate spray uniformity. This method retains spray traces for an extended period, facilitating subsequent analysis. During the tests, the Поток flow rate was set at 20 ml/min and 30 ml/min respectively, while the spray pressure was adjusted in gradients from low to high. Other wave soldering parameters remained fixed: conveyor speed 1400 mm/min, spray speed 380 mm/min, nozzle height 90 mm. The results indicated that spray uniformity performed well when the spray pressure was within the range of 0.035–0.040 MPa; whereas excessively low pressure (0.015–0.025 MPa) led to coarse flux particles and a significant decrease in spray uniformity.

In electronic soldering production, issues such as uneven residue on PCB surfaces and solder skipping occur frequently. In-depth analysis reveals that these problems are often closely related to the parameter settings of the wave soldering spray process. This paper focuses on the spray process, aiming to systematically identify various factors affecting spray uniformity. Through rigorous experimental verification and analysis, we have not only clarified the key influencing factors but also provided strong theoretical and technical support for the advancement of electronic wave soldering process technology.

With the continuous advancement of technology, electronic products are rapidly developing towards miniaturization and high density, placing increasingly higher demands on PCBA assembly processes. Especially against the backdrop of the widespread application of no-clean technology, the flatness of flux residue on PCB surfaces has become increasingly critical, and this flatness is directly influenced by the spray uniformity in wave soldering.

1 Problem Description

During the production process, after adopting a certain foreign brand of high-solid-content flux, the issue of excessive residue on PCB surfaces emerged. Observation under a high-power magnifier revealed that the residue easily entrapped oxides from the solder pot (Figure 1). If such residue accumulates in areas with fine pin pitches, it may lead to reduced insulation resistance, affecting product performance and reliability. Analysis indicates that besides being related to the flux characteristics, spray uniformity is also an important influencing factor for excessive residue.

2 Design of the Research Experiment Plan

2.1 Material Selection

Flux: A foreign brand of high-solid-content flux, namely Flux A, was selected. This product meets the requirements of "GB/T 31474-2015 Flux for High-Quality Internal Interconnections in Electronic Assembly" and its model complies with the IPC J-STD-004B ROL0 standard.

Printed Circuit Board Assembly (PCBA): Products from the same batch were used to ensure material consistency.

Wave soldering solder: SnCu0.7 was selected, conforming to the GB/T 31476-2015 "Solder for High-Quality Internal Interconnections in Electronic Assembly" standard.

Auxiliary materials and equipment include fax paper and wave soldering equipment, etc.

2.2 Formulation of the Test Plan

Based on product process requirements, using process test printed boards, the following test items were designed:

1) The influence of flow rate and air pressure on spray uniformity;

2) The influence of nozzle orientation changes on spray uniformity;

3) The corresponding spray effects for different nozzle orientations.

3 Test Process

3.1 Test on the Influence of Flow Rate and Air Pressure on Spray Uniformity

The fax paper test method is a common industry verification technique, as spray traces are long-lasting, facilitating detailed analysis.

3.1.1 Test Method

We set two different fixed Потокflow rates: 20 ml/min and 30 ml/min, while adjusting the spray pressure in gradients from low to high. Other wave soldering parameters remained constant, specifically: conveyor speed 1400 mm/min, spray speed 380 mm/min, nozzle height 90 mm. Spraying was conducted under different parameter combinations, and uniformity was assessed via the fax paper traces.

3.1.2 Test Results

The spray results under different flow rates and air pressure conditions are shown in Figures 2 and 3. The results show that when the flow rate is 20 ml/min or 30 ml/min, and the spray pressure is 0.035–0.040 MPa, the spray trace uniformity is good; when the pressure is below 0.015–0.025 MPa, the traces are uneven, with coarse particles and poor uniformity.

3.2 Test on the Influence of Nozzle Orientation on Spray Uniformity

This test aimed to analyze the influence of nozzle orientation on spray uniformity.

3.2.1 Test Method

Two parameter sets were established:

① Conveyor speed 1400 mm/min, spray speed 350 mm/s, nozzle height 90 mm, flow rate 40 ml/min;

② Conveyor speed 1200 mm/min, spray speed 350 mm/s, nozzle height 90 mm, flow rate 30 ml/min.

The nozzle orientation was adjusted separately, and uniformity was analyzed through fax paper traces.

According to the test pattern, light-colored areas on the fax paper indicate a larger amount of flux, while dark-colored areas indicate a smaller amount. Analysis shows: when the nozzle is vertically oriented, more flux accumulates near the PCB edge close to the conveyor claws, and the spray shape is more diffused; when the nozzle is parallelly oriented, more flux is deposited in the middle of the board, and the spray shape is more concentrated. This indicates a clear corresponding relationship between the wave soldering nozzle orientation and the spray effect.

3.3 Test on Spray Effects Corresponding to Different Wave Soldering Nozzle Orientations

This test primarily analyzes the influence of different wave soldering nozzle orientations and different nozzle heights on the corresponding spray effects and shape patterns.

3.3.1 Test Method

We adopted an offline spray experiment method, detaching the flux nozzle from the wave soldering equipment and placing it externally for testing. By adjusting different nozzle orientations, using a ruler to measure the actual spray height, fixing a PCB with attached fax paper at a set distance from the nozzle, activating theПотокspray for 3 seconds, and then conducting a comparative analysis of the spray effects to summarize the underlying patterns.

The specific test parameter settings are as follows:

① Selected spray heights: 50 mm, 70 mm, 100 mm, 120 mm;

② Nozzle orientations: vertical, parallel, 45°;

③ Flux flow rate: 25 ml/min, spray duration 3 s;

④ Fax paper attached to the PCB, placed at the set height to test spray effect;

⑤ Repeated experiments by adjusting nozzle orientation, spray height, air pressure, etc., to ensure reliable results.

3.3.2 Test Results

All experimental spray patterns were elliptical (Figure 7). After each set of experiments, we measured the length and width of the elliptical spray pattern on the fax paper and estimated the spray area by calculating the product of length and width. The data show that when the spray height was 70 mm and 100 mm, the corresponding unit areas were 2639 and 2781 respectively; whereas when the spray height was 50 mm and 120 mm, the unit areas were 2266 and 2639 respectively.

The results indicate that when the spray height is set within the 70–100 mm range, the resulting spray area is the largest, and the spray effect is optimal. When the spray height is lower, such as 50 mm, the spray area is smaller due to the close distance; when the spray height is too high, such as 120 mm, possibly affected by a combination of factors including spray pressure, flux properties, and gravity, the spray area also decreases relatively. The experimental results confirm that selecting a spray height within the 70–100 mm range can achieve the maximum spray area, which is an important condition for ensuring good uniformity.

4 Test Conclusions

Through a series of experimental verifications, we draw the following conclusions:

- Spray pressure is one of the key factors affecting spray uniformity. When the spray pressure is too low, the Поток particles become coarse, leading to poor spray uniformity. Different equipment each have a suitable spray pressure range. When the spray pressure increases beyond this range, further increasing the pressure will no longer change the uniform diffusion of the spray; at this point, increasing pressure only affects the upward force of the spray and does not influence diffusion uniformity.

- There is a clear and close correlation between the wave soldering nozzle orientation and the spray effect. Non-vertical nozzle orientations may lead to relatively poorer spray uniformity.

- Selecting a spray height between 70–100 mm enables the spray atomization area to reach its maximum, thereby creating favorable conditions for achieving good uniformity. When the distance between the flux nozzle and the PCB board is within this 70-100 mm range, the corresponding spray width is approximately 70 mm.

5 Concluding Remarks

To better ensure the uniformity of wave soldering spray, in actual production processes, it is necessary to clarify the orientation of the Потокnozzle orifice and the matching relationship between the air pressure and spray speed settings during production. However, due to the complexity of the actual production environment, the correspondence between these two can also be affected by other uncertain factors, such as pause times during the spray movement. Therefore, to thoroughly resolve and improve spray uniformity issues, more comprehensive optimization of the spray mechanism settings and related process parameters is key to enhancing uniformity.

This study provides strong theoretical and technical support for the development of electronic wave soldering process technology. It contributes to improving the soldering quality of electronic products, particularly in meeting the requirements for flux residue flatness on PCB surfaces under no-clean technology, and adapting to the development trends of miniaturization and high density in electronic products.

5 Conclusion

To better ensure the uniformity of the wave soldering spray, in the actual production process, it is necessary to clarify the orientation of the Поток nozzle orifice and the setting matching relationship between air pressure and spray speed in production. However, due to the complexity of the actual production environment, the corresponding relationship between the two will also be affected by other uncertain factors, such as the pause time during the spray movement. Therefore, to completely solve and improve the problem of spray uniformity, it is crucial to more comprehensively optimize the spray mechanism settings and related process parameters to enhance uniformity.

This research provides strong theoretical and technical support for the development of electronic wave soldering technology, which helps to improve the welding quality of electronic products, especially can meet the requirements for the flatness of flux residues on PCB surfaces under no-clean technology, and adapt to the development trend of miniaturization and high density of electronic products.