In the field of modern electronic manufacturing, surface mount technology (SMT) is the key to determining product miniaturization and precision. As the core process of SMT, the quality of reflow soldering directly affects the performance and reliability of the final product. With the increasingly stringent requirements for quality and cost control in the industry, reflow soldering in a nitrogen protected environment has become standard. The optimization core of this process is focused on precise monitoring and control of the concentration of trace oxygen (O ₂) in the protective atmosphere.

1、 The inevitability of precise control of oxygen demand in nitrogen protection

SMT nitrogen reflow soldering creates a low oxygen welding environment by injecting nitrogen into the furnace to replace oxygen. This move is mainly aimed at achieving two core objectives:

1. Inhibition of oxidation: When heat meets the metal surface, oxidation reaction is inevitable. Reducing environmental oxygen concentration is the fundamental means to prevent oxidation of solder pads, component pins, and solder materials themselves.

2. Improve wettability: A suitable low oxygen environment can effectively reduce the surface tension of molten solder, allowing it to spread and bond better, forming high-strength and aesthetically pleasing solder joints.

However, nitrogen protection is not simply about pursuing 'the lower the oxygen, the better'. Different products and process stages have refined requirements for oxygen content. Low concentrations may lead to cost increases, while high concentrations cannot effectively inhibit oxidation. Therefore, accurately stabilizing oxygen concentration within the target PPM (parts per million concentration) range is the key to achieving a balance between quality, cost, and efficiency.

Process quality corresponding to PPM levels of different oxygen concentrations:

Below 10 PPM: Suitable for applications such as chip level packaging that have zero tolerance for oxidation.

Approximately 100 PPM: It can achieve good weldability and accuracy, meeting the requirements of the vast majority of high reliability products.

1000 to 2000 PPM: This is a commonly used range that can achieve good wetting properties, but the effect is relatively ordinary.

Exceeding 2000 PPM: Only applicable to specific plate types, although the cost is low, the welding quality and consistency face challenges.

2、 The Four Core Benefits of Precise Trace Oxygen Detection

The introduction of high-precision and high response trace oxygen detection and analysis methods can significantly improve the reflow soldering process.

1. Significantly improve welding quality

Accurate oxygen concentration control provides an ideal environment for the formation of solder joints, minimizing common defects such as porosity, virtual soldering, and cold soldering. These microscopic defects are potential hazards that affect the long-term reliability of electronic devices, and precise oxygen concentration monitoring is the first line of defense to eliminate inferior solder joints from the source.

2. Enhance the long-term reliability of the product

The value of electronic products lies in their long-lasting and stable performance. The solder joints formed under the optimal oxygen concentration environment have better mechanical strength and electrical connection performance, thereby endowing the product with higher reliability and longer service life. Every solid solder joint is a cornerstone carefully crafted for the long-lasting operation of the product.

3. Achieve comprehensive cost optimization

Manufacturing efficiency is not only related to throughput, but also to resource utilization. Accurate oxygen concentration detection and closed-loop control can avoid excessive consumption of nitrogen and directly reduce gas costs. At the same time, by significantly reducing waste and rework caused by welding defects, manufacturers can achieve significant cost savings and truly achieve a win-win situation of quality and efficiency.

4. Ensure compliance with industry standards

In the highly regulated field of electronic manufacturing, strict control of process parameters is not only the best practice, but also a mandatory requirement to meet various international and industry standards (such as IPC standards). Accurate oxygen concentration detection and data recording provide strong proof of compliance, becoming the "passport" for products to enter the market and demonstrating the company's commitment to quality.

3、 Sifang Instrument Solution: Gasboard-3050 Series Trace Oxygen Analyzer

To meet the demand for low concentration oxygen detection in the semiconductor and electronic manufacturing industries, Sifang Instrument has successfully launched the Gasboard-3050 series low concentration oxygen analyzer based on its deep technical accumulation in the field of zirconia sensors. This series of products provides precise data support for process optimization with its 0.1 ppm resolution and wide range coverage (0-10 ppm to 100% O ₂).

Figure 1: Sifang Instrument Zirconia Sensor Production Line and Different Types of Zirconia Sensor Chip Products

Among them, the Gasboard-3052 multi-channel trace oxygen analyzer is a closed-loop control solution tailored for modern reflow soldering furnaces.

Figure 2 Gasboard-3052 Trace Oxygen Analyzer

Figure 3 Closed loop control gas path diagram of nitrogen gas flow in reflow soldering furnace

Figure 4: Closed loop control design of nitrogen gas flow in the reflow soldering furnace of Gasboard-3052

Core Technologies and Features:

High precision multi-channel monitoring: using a fast response zirconia sensor (T90<5s), supporting wide range measurement from 1ppm to 30%. Supports multi-channel automatic switching sampling and can customize the functions of each channel (fixed monitoring or priority control), maintaining control accuracy even under round robin measurement.

Intelligent closed-loop control: The instrument integrates PFC (Proportional Flow Control) module, based on programmable PID algorithm, which can dynamically adjust the nitrogen valve opening of each injection zone according to real-time measured oxygen concentration data. This' soft control 'strategy avoids frequent mechanical wear of valves and achieves precise and flexible atmosphere management.

Stability and ease of use: Equipped with field validated zirconia sensors, it has excellent reproducibility and long-term stability. It only takes 3-5 minutes for preheating to start working, and provides rich communication interfaces (RS-232/RS-485) and analog outputs for system integration.

Core value created for customers:

Energy saving and cost reduction: By avoiding nitrogen waste and reducing heating energy consumption, we help customers achieve a comprehensive energy saving rate of over 30%.

Plug and play: The product has passed the system integration verification of mainstream reflow soldering furnace manufacturers, greatly reducing deployment and debugging time.

• Improve yield: Provide solid support for the welding environment and directly improve product pass rates.

In SMT reflow soldering process, precise control of trace oxygen concentration has evolved from an optimization measure to a core technology link that determines manufacturing competitiveness. The Gasboard-3050 series analyzer from Sifang Instruments is becoming a trusted choice for electronic manufacturers to optimize processes, reduce costs and increase efficiency, and win the future with its accuracy, intelligent control strategy, and reliable performance.