How to Reduce the Formation of Tin Balls in NeoDen IN6 Reflow Oven?

Introduction

Tin balls are one of the most common soldering defects in the SMT reflow oven soldering process. For electronics manufacturers, even a small number of tin balls can reduce the insulation clearance on the PCB surface, increase the risk of short circuits, and even affect the long-term reliability of the product. Particularly in industries with high soldering quality requirements—such as automotive electronics, industrial control, and medical devices—reducing tin balls has always been a key focus for SMT process engineers.
This article will analyze the primary causes of tin ball formation based on the NeoDen IN6 user manual and actual SMT production processes, and share how to effectively reduce tin balls and improve first-pass soldering yield by optimizing the reflow soldering process.

What Are Tin Balls? Why Do They Affect SMT Product Quality?

Tin balls refer to tiny solder particles scattered around solder joints or on the PCB surface after the reflow soldering process is complete. They typically originate from solder powder in the solder paste that fails to properly coalesce at the solder joints during heating and instead adheres to the PCB surface as separate small spheres.
Depending on their location, tin balls can generally be categorized into several typical scenarios. For example, they may be distributed on either side of small-sized components such as chip resistors and capacitors, appear near IC pins, adhere to the surface of the solder mask, or be concentrated in areas with fine-pitch components. Although these tin balls are small in size, they may shift due to product vibration, thermal cycling, or long-term use, thereby posing a potential risk of electrical short circuits.
It is worth noting that solder balls do not necessarily indicate a failure in the reflow soldering process. In fact, solder balls can form at any stage—from solder paste printing through SMT placement, preheating, reflow, and cooling. Therefore, engineers need to conduct a systematic analysis of the entire SMT process rather than simply adjusting a single equipment parameter.

7 Main Causes of Solder Beads in Reflow Oven Soldering

1. Excessively Fast Preheating Rate Leading to Rapid Flux Evaporation

Once the PCB enters the preheating stage, the flux in the solder paste needs to evaporate gradually to fully activate the pad surfaces. If the heating rate is too fast, the flux will evaporate rapidly in large quantities, causing the solder powder to be blown away by the gas flow and ultimately forming solder beads.
NeoDen IN6 user manual recommends keeping the heating rate at approximately 1°C/s until the PCB temperature reaches 160°C. If heating is too rapid, it may not only cause PCB warping but also prevent the flux from fully activating, thereby increasing the likelihood of solder balls forming.
Recommended temperature profiles vary by solder paste brand. Therefore, when setting zone parameters, prioritize the reflow profiles provided by the solder paste supplier and fine-tune them based on the specific PCB, rather than directly applying fixed temperatures.

2. Improper Conveyor Speed Settings Resulting in Insufficient PCB Heating Time

Many companies increase conveyor speed to boost production capacity. However, if a PCB enters the reflow zone before it has been sufficiently preheated, volatiles in the solder paste cannot be fully expelled. This makes the PCB prone to spatter the moment the solder melts, ultimately resulting in a large number of solder balls.
NeoDen IN6 user manual states that the conveyor speed not only affects the total heating time but also directly determines how the PCB is heated in each temperature zone. For thick boards, multilayer boards, or PCBs with high component density, the conveyor speed should be appropriately reduced to allow the entire PCB to absorb heat sufficiently, thereby achieving more uniform reflow soldering. Conversely, for single-sided boards or products with fewer components, the speed can be appropriately increased based on actual conditions to improve production efficiency.

3. Improper Temperature Profile Settings

NeoDen IN6 user manual states that an ideal reflow soldering temperature profile typically consists of four stages: Preheat, Soak/Active, Reflow, and Cooling. Each stage serves a different process function: the preheat zone is responsible for a gradual temperature rise, the soak/active zone allows the flux to fully activate and the solvents to evaporate, the reflow zone completes the melting of the solder, and the cooling zone helps form a stable, dense solder joint structure.
NeoDen IN6 user manual recommends that the peak temperature should generally be 20–40°C higher than the solder paste melting point, with the liquid phase time controlled between 10 and 60 seconds. If the peak temperature is too low, the solder paste cannot melt sufficiently. If the temperature is too high or the reflow time is too long, it can easily lead to solder oxidation, excessive heat on the PCB, and even increase the likelihood of solder balls, cold joints, and other soldering defects.
Therefore, when optimizing the process, adjustments should always be based on the temperature profile recommended by the solder paste manufacturer, taking into account the PCB size, number of layers, copper thickness, and component density—rather than simply copying parameters from other products.

4. Solder Paste Quality or Moisture in the PCB

If the solder paste has exceeded its shelf life, been stored at an improper temperature, not been sufficiently brought to room temperature, or not stirred thoroughly, this may lead to a decrease in flux activity, increasing the likelihood of solder splatter. Similarly, if a PCB has absorbed a significant amount of moisture after prolonged storage in a humid environment, the moisture will rapidly expand upon entering the reflow oven, which can also cause the molten solder to form solder balls.
NeoDen IN6 user manual explicitly states in its fault analysis section that solder balls may be related to substandard solder paste quality, repeated PCB printing, or PCBs that are unclean or insufficiently dried, and recommends keeping PCBs clean and dry before production.
For production environments with high humidity, it is recommended to add a PCB drying process before formal production and to strictly follow the solder paste manufacturer’s requirements for storage, acclimatization, and use to reduce soldering risks caused by material factors.

5. Inadequate Thermal Balance Between Upper and Lower Heating Zones and Insufficient Equipment Maintenance

In the troubleshooting recommendations of the NeoDen IN6 user manual, if excessive top heating is found to be causing soldering abnormalities, the temperature of the upper heating zone can be appropriately reduced, and bottom heating increased to ensure more uniform heating of the entire PCB.
In addition, equipment maintenance must not be overlooked. The NeoDen IN6 features a built-in solder fume filtration system. The manual recommends replacing the filter periodically based on usage frequency, its typical service life is approximately 8 months. If the filter remains clogged for an extended period, hot air circulation efficiency decreases, which may affect temperature uniformity inside the oven and, consequently, soldering consistency. Additionally, high-temperature lubricant must be applied to the conveyor chain bearings regularly to ensure a stable conveyor speed.

How to Use the NeoDen IN6 to Reduce Solder Balls and Improve Soldering Yield?

NeoDen IN6 offers several features that aid in process optimization, enabling engineers to establish a stable reflow soldering process in a more scientific manner.

• The equipment features a total of 6 heating zones—three on top and three on the bottom—along with a full hot-air circulation structure, ensuring more uniform heating of the PCB. high-sensitivity temperature sensors maintain temperature stability within ±0.2°C, providing a consistent soldering environment for different product batches.
• The NeoDen IN6 supports temperature curve data collection. Engineers can mount temperature sensors directly on production PCBs to record complete reflow temperature curves using the equipment. By comparing these curves with those recommended by solder paste manufacturers, they can quickly identify issues such as insufficient preheating, excessively short isothermal times, or peak temperature deviations.
• The equipment supports SAVE and LOAD functions for multiple sets of process parameters. For EMS factories that frequently switch between different products, conveyor speeds and temperature zone parameters corresponding to different PCBs can be saved in advance and directly recalled for the next production run, reducing repetitive debugging time while minimizing soldering defects caused by human configuration errors.

For small- to medium-volume production and R&D prototyping, these features not only improve process stability but also significantly shorten the new product introduction cycle.

FAQ

Q1. Why do so many solder balls appear after reflow soldering?

A. The most common causes include excessive heating rates, improper conveyor speed settings, poorly designed temperature profiles, degraded solder paste quality, and moisture absorption by the PCB. It is recommended to perform debugging according to the solder paste manufacturer’s recommended profile and to combine this with temperature profiles tested on actual PCBs, rather than adjusting the temperature of a single zone alone.

Q2. How does the NeoDen IN6 help reduce solder balls?

A. NeoDen IN6 supports engineers in establishing stable reflow soldering processes through features such as full hot-air circulation, six-zone heating, high-precision temperature control (±0.2°C), temperature curve data logging, and the ability to save multiple sets of process parameters. When equipment parameters are combined with suitable solder paste, PCBs, and process management, the system can effectively reduce solder balls and other soldering defects, thereby improving first-pass yield.

Conclusion

There is no so-called "one-click solution" for reducing solder balls. Truly stable SMT production relies on the comprehensive optimization of equipment performance, temperature profiles, conveyor speed, solder paste quality, and daily maintenance.
NeoDen IN6 user manual provides a comprehensive overview of reflow soldering principles, temperature profile setup methods, and troubleshooting recommendations, serving as a reliable reference for engineers to establish standardized processes. By properly controlling the heating rate, optimizing conveyor speed, establishing temperature profiles that meet solder paste requirements, and combining these with regular equipment maintenance, common soldering defects such as tin balls, cold joints, and solder bridges can be effectively reduced, further improving the yield and consistency of SMT production lines.

If you are looking for a desktop-level reflow soldering system that balances precision, stability, and cost-effectiveness, the NeoDen IN6 can meet the diverse needs of R&D prototyping, small-batch production, and small-to-medium-sized EMS companies.

Please contact the NeoDen SMT expert team to obtain product documentation for the NeoDen IN6, process parameter recommendations, and professional SMT solutions. Whether you are an electronics R&D lab, a hardware startup, or an EMS factory expanding production, we can provide you with more efficient and reliable reflow soldering equipment and process support tailored to the characteristics of your PCB products.