With the development of electronic information industry, terminal electronic products have higher and higher requirements for the refinement of PCB industry. Drilling is an important step in PCB manufacturing, which has been developed to the minimum hole diameter of 0.08mm, the maximum hole spacing of 0.1mm or even higher level. In addition to conducting holes, parts holes, grooves, special-shaped holes, plate shape, etc., all need to be checked. How to detect the drilling quality of PCB board efficiently and accurately has become an important link to ensure the quality of products. PCB hole inspection machine is just an automatic optical inspection equipment used in the quality inspection of drilling. The purpose of this paper is to analyze the function of hole testing machine in drilling process and provide reference experience for PCB manufacturers.

In PCB drilling process, it is necessary to control the following possible quality problems: porosity, leakage, displacement, wrong drilling, non-penetration, hole loss, waste, front, plug hole. At present, the control methods of various manufacturers are mainly to standardize the drilling process before drilling and strengthen the inspection means after drilling. In actual production, because the pre-drilling method can only reduce the probability of error, can not completely eliminate, we must rely on post-drilling inspection to ensure product quality.

In the post-drilling inspection, many domestic manufacturers are still using the plug gauge combined with artificial visual film (film) set inspection method: through the plug gauge focus on checking the hole, hole small, through the film focus on porous, leaky hole, shift, not through, not through, other hole damage, front, hole plug through artificial visual to complete. In the use of film inspection, each product drilling drill out a red film sample, inspection through the pin and product plate fixed, manual visual inspection under the light box. In theory, this method can detect all kinds of defects, but in practice, the effect is greatly discounted.

The main problems are as follows:

First, the inspection requirements of small aperture can not be guaranteed: production practice shows that for PCB with minimum aperture ≥0.5mm, manual can achieve higher inspection results under the premise of ensuring a certain production efficiency. This is determined by the minimum discernable visual Angle of the human eye, the working distance, and the attention span. With the decrease of aperture size, for the product plate below 0.5mm, the inspection ability of human eyes will rapidly decline, for the product plate ≤0.25mm, manual even sampling quality is difficult to ensure.

Second, the efficiency of manual inspection is limited: the efficiency of manual inspection is directly related to the number of holes and the minimum aperture. The actual production experience shows that the efficiency will be significantly reduced when the hole is more than 10000 and the smallest hole is less than 0.5mm. Manual inspection is only suitable for sampling. For high density plate, it is impossible to guarantee the quality of drilling by manual.

Third, the stability of quality can not be guaranteed: people will be affected by experience, mood, fatigue, responsibility and other factors, it is difficult to ensure the stability of quality. Some manufacturers can not use multiple artificial, repeated inspection method, but still can not ensure the stability of quality.

In order to solve the above problems, many LARGE PCB factories have adopted hole inspection AOI equipment to replace manual labor in a large range. Especially for Japanese and Taiwan-funded enterprises, many years of practice has proved the effectiveness of this new method, which is worth the attention and reference of many domestic PCB manufacturers.

AOI hole inspection equipment belongs to automatic optical inspection equipment. According to the image form of various defects of drilling, it can be divided into: porous, less hole, large hole, small hole, residual, hole deviation and hole shape. It is divided into two kinds: one is Hole inspection machine, the other is Hole measurement and inspection machine (hole-AOI). In practice, there is also an X-ray inspection machine, which is mainly used for the analysis of buried blind holes and multi-layer boards, which is inconsistent with the objective of manual film jacket inspection and does not belong to the analysis scope of this paper.

According to PCB manufacturers’ equipment matching experience, it is recommended to use multiple sets of hole checking machine for full inspection of the first plate and bottom plate, focusing on the inspection of holes, few holes, large holes, small holes and debris; A hole position measuring and checking machine is used for spot check, focusing on hole deviation. The characteristics of the two devices are as follows:

Hole checking machine: the advantages are low price, fast inspection efficiency, check a 600mm×600mm PCB average of 6~7 seconds, can realize the porous, less hole, hole, small hole, residual inspection. The disadvantage is that the ability to check the hole position is not high, and only serious defects can be detected. According to the manufacturer’s actual production experience, generally 15 RIGS are equipped with 1 hole checking machine.

Hole position measuring and checking machine: the advantage is that all items can be checked. The disadvantage is that the price is high (about 3~4 times of the hole inspection machine), the inspection efficiency is low, it takes several minutes or even longer to check 1 piece. It is generally recommended to configure one machine for product sampling inspection to supplement the deficiency of hole checking machine for hole position inspection.

Inspection principle of hole inspection AOI equipment: PCB drilling image is collected by optical system, and compared with the design document (drill tape file or Gerber file). If the two are consistent, it indicates that the drilling is correct; otherwise, it indicates that there is a problem in the drilling, and then analyze and classify the defect type according to the image morphology. The hole inspection equipment is compared with the design documents of drilling, and the manual visual inspection is compared with the film. In terms of the inspection principle, the problems caused by the film drilling errors can be avoided, and the reliability is higher.

PCB hole testing machine technology analysis

The role of hole checking machine on PCB drilling process is reflected in the following aspects:

First, efficient and stable drilling quality inspection:

Routine inspection: porous, less porous, large hole, small hole and debris defects can be checked simultaneously at the speed of minimum aperture 0.15mm and 8m/min, and the defect location is marked and the defect image is reviewed to provide manual judgment basis.

Debris inspection: in the first drilling inspection, debris is not the focus of the most attention; But before electroplating, debris should cause enough attention. In order to reduce the influence of debris on the quality of copper precipitation, PCB manufacturers generally remove debris by grinding and cleaning before electroplating, but in practice, it is still not 100% clean, the more high density plate cleaning effect is worse. Theoretically, there are scraps in every PCB, so it is impossible to fully inspect all the holes on all products, relying on manual visual inspection, but the hole inspection machine makes it possible.

Quality improvement: stability is the biggest advantage of equipment, stable product quality can enhance the brand influence of PCB factory, directly improve the ability of manufacturers to receive orders.

Second, assist production and quality departments in data statistical analysis:

Tool analysis: it can analyze the average deviation of drilling hole diameter of different drilling tools in PCB, monitor the possible drilling tool wear in real time, find the wrong tool problem in time, and avoid batch waste plates.

Capacity analysis: it can collect daily, monthly, quarterly and annual production capacity and average production efficiency, provide analysis data for various control methods, and improve factory operation and management ability.

Machine analysis: can count the output, variety and quality problems of each rig, improve the ability to manage the details of the machine.

Third, cost saving, high input-output ratio:

Inspection personnel: on the premise of ensuring quality and improving efficiency, 2~3 inspection personnel can be saved on average by a hole inspection machine.

Raw material: it can save the material cost of film, which is more meaningful for medium and small batch factories.

Customer complaint: it can save the cost of return order and fine caused by drilling defects. Although it is not as direct as the personnel and materials saved, the average annual cost saved is even higher than the purchasing cost of hole inspection machine.

With PCB manufacturers’ higher quality requirements for drilling process, under the pressure of increasing labor cost and gradually inadequate manual inspection ability, the importance of hole inspection machine is becoming increasingly obvious.

The use of the hole inspection machine has been more than ten years, the function and performance of the equipment has been constantly improving, and the degree of cooperation with the production is more and more close. Especially with the rapid development of high-density board, hole inspection machine has been gradually transformed from the original auxiliary equipment into a key supporting equipment. In the equipment transformation of many PCB old plants and the preparation of new plants, the popularity of hole testing machine equipment will be more and more high.