PCB Technical - Technical Analysis of PCB Hole Inspection Machine

With the development of the electronic information industry, terminal electronic products have higher and higher requirements for the refinement of the PCB industry. Drilling is an important part of PCB manufacturing, and it has been developed to a minimum hole diameter of 0.08mm and a minimum hole spacing of 0.1mm or even higher. In addition to via holes, component holes, slot holes, special-shaped holes, board shape, etc., all need to be checked. How to efficiently and accurately inspect the drilling quality of PCB boards has become an important part of ensuring product quality. PCB hole inspection machine is a kind of automatic optical inspection equipment used in drilling quality inspection. This article aims to briefly analyze the role of the hole inspection machine in the drilling process and provide reference experience for PCB manufacturers.

In the PCB drilling process, it is necessary to control the following quality problems that may occur: porosity, leakage, displacement, wrong drilling, impermeability, hole damage, partial waste, piercing, and plugging. At present, the management and control methods of various manufacturers mainly include standardizing drilling rig operation technology before drilling and strengthening inspection methods after drilling. In actual production, because the pre-drilling method can only reduce the probability of errors, it cannot be completely eliminated, and the post-drilling inspection must be relied on to ensure product quality.

In post-drilling inspections, many domestic manufacturers are still using plug gauges combined with manual visual film (film) inspection and comparison methods: the plug gauges are used to check the large and small holes, and the film to check the holes, leaks, and holes. Displacement, non-penetration, impermeability, other hole damage, piercing, hole plugs, etc. are completed by manual visual inspection. The main problems are reflected in:

First, the inspection requirements for small-size apertures cannot be guaranteed: production practice shows that for PCBs with a minimum aperture of ≥0.5mm, manual labor can achieve a higher inspection effect while ensuring a certain production efficiency. This is determined by the minimum recognizable viewing angle of the human eye, working distance, and duration of attention. As the aperture size decreases, the inspection ability of the human eye will decline rapidly for product boards below 0.5mm. For product boards ≤0.25mm, it is difficult to ensure the quality of manual inspection.

Second, the efficiency of manual inspection is limited: the efficiency of manual inspection is directly related to the number of holes and the minimum hole diameter. The actual production experience shows that the efficiency will be significantly reduced when the hole is more than 10,000 holes and the smallest hole is less than 0.5mm, and manual inspection is only suitable for random inspection. For high-density boards, relying on manual labor can no longer guarantee the quality of drilling.

Third, the stability of quality cannot be guaranteed: labor will be affected by many factors such as experience, mood, fatigue, and sense of responsibility, and it is difficult to guarantee the stability of quality. Some manufacturers are not allowed to use multiple manual and repeated inspection methods, but they still cannot ensure the stability of quality.

The hole inspection AOI equipment belongs to the automatic optical inspection equipment. According to the image morphology of the various defects of the drilling, it is divided into: multiple holes, few holes, large holes, small holes, debris, hole deviation, and hole shape. There are two types: one is hole inspection machine, and the other is hole position measurement and inspection machine (Hole-AOI). In practice, there is also an X-Ray inspection machine, which is mainly used for buried blind vias and multi-layer board alignment analysis, which is inconsistent with the goal of artificial film set inspection and does not belong to the analysis scope of this article.

According to the equipment supporting experience of PCB manufacturers, it is recommended to use multiple sets of hole inspection machines for the full inspection of the first board and bottom board, focusing on the inspection of multiple holes, few holes, large holes, small holes, and debris; use 1 hole position measurement and inspection machine to do Sampling inspection, focusing on the hole deviation. The characteristics of the two devices are as follows:

Hole inspection machine: The advantages are low price and fast inspection efficiency. It can inspect 1 piece of 600mm*600mm PCB in an average of 6~7 seconds, which can realize the inspection of multiple holes, few holes, large holes, small holes, and debris. The disadvantage is that the hole position inspection ability is not high, and only serious defects can be detected. According to the actual production experience of the manufacturer, 15 drilling rigs are generally equipped with 1 inspection machine on average.

The inspection principle of the hole inspection AOI equipment: the optical system is used to collect the PCB drilling imaging and compare it with the design file (drilling tape file or Gerber file). Analyze and classify the types of defects according to the image morphology. The hole inspection equipment is compared with the drilling design documents, and the manual visual inspection is compared with the film. The inspection principle can avoid the problems caused by the error of the film drilling, and the reliability is higher.

The effect of the hole inspection machine on the PCB drilling process is reflected in the following aspects:

First, efficient and stable drilling quality inspection:

Routine inspection: at the minimum pore diameter of 0.15mm, 8m/min, simultaneous inspection of multiple holes, few holes, large holes, small holes, and debris defects, and mark the position of the defect, Review the defect image, and provide manual judgment in accordance with.

Debris inspection: In the first inspection of drilling, debris is not the focus of the most attention; but before electroplating, debris should be paid attention to. In order to reduce the impact of debris on the quality of copper sinking, PCB manufacturers generally remove the debris by grinding and cleaning before electroplating, but in practice it still cannot be 100% completely cleaned. The more high-density boards, the worse the cleaning effect. . In theory, there will be debris on every PCB, so it is unrealistic to rely on manual visual inspection to require a full inspection of all drilling holes of all products, but it is possible to use a hole inspection machine.

Quality improvement: Stability is the biggest advantage of the equipment. Stable product quality can enhance the brand influence of PCB factories and directly improve the manufacturers' ability to receive orders.

Second, statistical analysis of data in auxiliary production and quality departments:

Tool analysis: It can analyze the average deviation of the hole diameter of the different drills in the PCB, monitor the possible wear of the drill in real time, find the problem of the wrong tool in time, and avoid batch waste of boards.

Production capacity analysis: It can calculate daily, monthly, quarterly, and annual production capacity and average production efficiency, provide analysis data for various control methods, and improve factory operation and management capabilities.

Machine station analysis: It can count the output, variety and quality problems of each drilling rig, and improve the detailed management ability of the machine.

Third, cost saving, high input-output ratio:

Quality inspection personnel: On the premise of ensuring quality and improving efficiency, one hole inspection machine can save 2 to 3 quality inspection personnel on average.

The hole inspection machine has been in use for more than ten years. The function and performance of the equipment have been continuously improved, and the coordination with PCB production has become more and more closely. Especially with the rapid development of high-density boards, the hole inspection machine has gradually changed from the original auxiliary equipment to the key supporting equipment. In the equipment transformation of many old PCB factories and the preparation of new factories, the popularity of hole inspection equipment will become higher and higher.