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 link in 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 and component holes, there are also slot holes, special-shaped holes, board shapes, etc., which need to be checked. How to efficiently and accurately detect the drilling quality of PCB boards has become an important link to ensure product quality. PCB hole inspection machine is an 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 mainly control the following quality problems that may occur: porosity, leakage, displacement, mis-drilling, non-penetration, hole damage, partial waste, burrowing, and plugging. At present, the management and control methods of various manufacturers are mainly to standardize the operation process of drilling rigs before drilling, and to strengthen inspection methods after drilling. In actual production, since pre-drilling methods can only reduce the probability of errors, but cannot completely eliminate them, post-drilling inspection must be relied on to ensure product quality.
In the post-drilling inspection, many domestic manufacturers are currently still adopting the method of plug gauge combined with manual visual film (film) set inspection and comparison: the plug gauge focuses on checking the large and small holes, and the film focuses on checking holes, leaks, holes, etc. Displacement, non-piercing, non-penetrating, and other hole damage, front covering, hole plugging, etc. are completed by manual visual inspection. When using film inspection, a red film sample is first drilled for each product, fixed with the product board by pins during inspection, and visually inspected manually under the light box. This method can detect various defects in theory, but the actual effect is greatly discounted.
The main problems are reflected in:
1. The inspection requirements for small-sized apertures cannot be guaranteed: production practice shows that for PCBs with a minimum aperture ≥ 0.5mm, manual inspection can achieve a higher inspection effect under the premise of ensuring a certain production efficiency. This is determined by the minimum recognizable viewing angle of the human eye, the working distance, and the duration of attention. As the aperture size decreases, for product boards below 0.5mm, the inspection ability of human eyes will drop rapidly, and for product boards ≤0.25mm, it is difficult to guarantee the quality of manual random inspection.
2. 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. Actual production experience shows that when there are more than 10,000 holes and the smallest hole is less than 0.5mm, the efficiency will be significantly reduced, and manual inspection is only suitable for random inspection. For high-density boards, relying on manual work can no longer guarantee the quality of drilling.
3. The stability of quality cannot be guaranteed: Human labor will be affected by many factors such as experience, emotion, fatigue, sense of responsibility, etc., and it is difficult to guarantee the stability of quality. Some manufacturers are forced to adopt multi-channel manual and repeated inspection methods, but they still cannot ensure the stability of quality.
In order to solve the above problems, many PCB manufacturers have adopted hole inspection AOI equipment on a large scale to replace labor. Especially for Japanese-funded enterprises and Taiwan-funded enterprises, many years of practice have proved the effectiveness of this new method, which deserves the attention and reference of many domestic PCB manufacturers.
Hole inspection AOI equipment belongs to automatic optical inspection equipment. According to the image form of various defects in drilled holes, it can be divided into: multi-hole, few holes, large holes, small holes, debris, hole deviation, and hole shape. Specifically divided into two types: one is the hole inspection machine, and the other is the hole position measurement inspection machine (Hole-AOI). In practice, there is also an X-Ray inspection machine, which is mainly used for the alignment analysis of buried blind holes and multi-layer boards. It is inconsistent with the goal of manual film set inspection and does not belong to the analysis scope of this article.
According to the equipment matching experience of the PCB manufacturer, it is recommended to use multiple sets of hole inspection machines to do the full inspection of the first board and the bottom board, focusing on checking porous, few holes, large holes, small holes, and debris; use a hole position measurement inspection machine to do Sampling inspection, focusing on checking hole deviation. The characteristics of the two devices are as follows:
Hole inspection machine: The advantages are low price and fast inspection efficiency. It takes an average of 6~7 seconds to inspect a PCB of 600mm×600mm. It can realize the inspection of porous, few holes, large holes, small holes, and debris. The disadvantage is that the ability to check the hole position is not high, and only serious defects can be detected. According to the actual production experience of the manufacturer, generally 15 drilling rigs are equipped with 1 hole inspection machine on average.
Hole position measurement inspection machine: the advantage is that it can realize the inspection of all items. The disadvantage is that the price is high (about 3~4 times that of the hole inspection machine), the inspection efficiency is low, and it takes several minutes or even longer to inspect one piece. Generally, it is recommended to configure one machine for random inspection of products, supplementing the deficiency of the hole inspection machine for hole position inspection.
The inspection principle of the hole inspection AOI equipment: use the optical system to collect the PCB drilling image, and compare it with the design file (drilling file or Gerber file). When the two are consistent, it means that the drilling is correct; According to the image morphology analysis, classify the type of defect. The hole inspection equipment is compared with the design file of the drill hole, and compared with the film during manual visual inspection. In terms of inspection principle, it can avoid problems caused by film drilling errors, and has a higher degree of reliability.
The effect of the hole inspection machine on the PCB drilling process is reflected in the following aspects:
1. Efficient and stable drilling quality inspection:
Routine inspection: At a minimum aperture of 0.15mm and a speed of 8m/min, it can simultaneously inspect porous, few, large, small, and debris defects, and mark the position of the defect and review the image of the defect to provide manual judgment in accordance with.
Debris inspection: Debris is not the most important point in drilling first article inspection; but before electroplating, detritus should be given enough attention. In order to reduce the impact of debris on the quality of sinking copper, PCB manufacturers generally remove debris by grinding and cleaning before electroplating, but in practice, it is still not 100% completely cleaned, and the cleaning effect is worse for high-density boards. . Theoretically, every PCB will have debris, so it is unrealistic to require full inspection of all drilling holes of all products, relying on manual vision, but the use of hole inspection machines makes it possible.
Quality improvement: Stability is the biggest advantage of equipment. Stable product quality can enhance the brand influence of PCB factories and directly improve the ability of manufacturers to receive orders.
2. Statistical analysis of data in auxiliary production and quality departments:
Tool analysis: It can analyze the average deviation of the drilling diameter of different drills in the PCB, monitor the possible wear of the drills in real time, find the problem of wrong tools in time, and avoid batch waste of boards.
Production capacity analysis: It can count 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 analysis: It can count the output, variety and quality problems of each drilling rig, and improve the detailed management ability of the machine.
3. Cost saving, high input-output ratio:
Quality inspectors: On the premise of ensuring quality and improving efficiency, one hole inspection machine can save 2~3 quality inspectors on average.
Raw materials: It can save the material cost of film, which is more meaningful for small and medium batch factories.
Customer complaints: It can save the cost of chargeback and fines caused by drilling defects. Although it is not directly calculated like the saved personnel and materials, the average annual cost savings is even higher than the purchase cost of the hole inspection machine.
With the higher quality requirements of PCB manufacturers for drilling technology, under the pressure of increasing labor costs and gradually incompetent manual inspection capabilities, the importance of hole inspection machines is becoming more and more obvious.
The hole inspection machine has been used for more than ten years, and the functions and performance of the equipment have been continuously improved, and the degree of cooperation with production is getting closer and closer. 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.
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