1. Circuit boards, circuit boards, PCB boards, and PCB soldering technology have seen significant advancements in recent years alongside the development of the electronic industry.

2. A noticeable trend is the rise of reflow soldering technology. In principle, traditional through-hole components can also be reflow soldered, which is commonly known as through-hole reflow soldering.

3. The main advantage of this method is the ability to complete all solder joints simultaneously, thereby minimizing production costs.

4. However, the application of reflow soldering is limited by temperature-sensitive components, affecting both through-hole and SMD parts.

5. Consequently, attention has shifted towards other soldering methods. In many applications, selective soldering can follow reflow soldering.

6. Below is an overview of the quality inspection methods for PCB circuit board soldering.

7. Currently, inspection methods for PCB soldering quality include visual inspection, infrared detection, and online testing methods, among others.

8. Among these methods, the most economical and widely used is visual inspection, known for being cost-effective, convenient, simple, and feasible.

9. The other methods typically require specific equipment, which, despite the higher investment, can ensure greater inspection reliability.

10. ★Visual method

11. The visual method relies on the human eye to directly observe the solder joint surface, allowing for the detection of poor wettability, inappropriate solder volume, pad separation, bridging, solder ball splashing, dull solder joints, and missing solder.

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1. **Defect Detection**

The simplest tool for visual inspection is a magnifying glass. Typically, a fixed magnifying glass with 5 to 10 times magnification is employed, which is adequate for inspecting the soldering of low-density circuit boards. However, the drawback of this tool is that inspectors can experience fatigue. A more effective visual inspection instrument is a camera-type screen display inspector, which offers adjustable magnification up to 80 to 90 times. This device displays the solder joints on a screen via a CCD, allowing inspectors to observe it as they would a television. Higher-grade inspection instruments can automatically maneuver the circuit board in two directions and can also position it to focus on critical areas of the PCBA. Additionally, these devices can be equipped with video recorders to document inspection results.

2. **Infrared Detection Method**

The infrared detection method utilizes infrared beams to heat the solder joints on the circuit board, subsequently monitoring the heat release curve to determine whether there are voids within the solder joints. This technique serves as an indirect inspection of welding quality. It is most suitable for high-volume, automated soldering, provided there is good pad consistency and minimal variation in component size. Otherwise, external factors can significantly affect the heat dissipation characteristics of the solder joints, increasing the false detection rate. Due to the various limitations, such as the differing sizes of solder joints across circuit board types, this method is less frequently used in electronic product testing—according to Shanghai PCB Welding Friendship.

3. **X-ray Perspective**

X-ray fluoroscopy capitalizes on the principle that X-rays have limited ability to penetrate solder compared to materials like copper, silicon, and FR-4. This method reveals the density distribution of solder thickness, shape, and quality. It is particularly effective for inspecting hidden solder joints (i.e., concealed soldering). The circuit board under examination is placed in the X-ray channel, allowing viewers to observe how the solder joint obstructs the X-ray beam, outlining its contour.

4. **Online Test Method**

The online test method employs an online tester, which connects the test points on the circuit board to the tester via a signal connection component known as the “bed of needles.” This setup allows for checking open circuits, short circuits, and faulty components, as well as verifying component functions such as resistance and capacitance values, and the polarity of transistors. The IC’s dummy solder pins can be evaluated using the IC floating pin test method. In cases where the circuit board has a high component density, making it challenging to establish the necessary test points, boundary scan technology can be utilized to consolidate those points through a designed test circuit to the edge connector of the soldering. This enables the online tester to measure required points across various locations.

5. The online test method serves as an electrical signal testing technique that assesses the soldering status of PCBs. This inspection closely mirrors real-world conditions; typically, circuit board welds tested online can be installed in machines. However, it does not provide definitive quality results for the soldering, and the reliability of the solder joints cannot be intuitively verified.

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