Takayuki Murakoshi

Automated Solder Inspection Technique for BGA-Mounted Substrates by Means of Oblique Computed Tomography

High-density large-scale integration (LSI) packages such as ball grid arrays (BGAs) are being utilized in car electronics and communication infrastructure products. These products require a high speed and reliable inspection technique for their solder joints. Oblique computed tomography (OCT) was proposed as a novel imaging technique for BGA-mounted substrates, and it is being introduced in many manufacturing factories. Although operators examine OCT images manually, the establishment of an automated inspection technique is required from the viewpoint of an operators load and the fluctuation of the inspection results. In this paper, a novel automated solder inspection technique by means of OCT is proposed. This technique consists of position adjustment, bump extraction, character extraction and judgement. Moreover, by combining five characteristic features, the condition of a solder bump was determined in computer algorithm. In this paper, linear discriminate analysis and an artificial neural network technique are introduced as the determination methods. In the experiments, these techniques are evaluated by using actual BGA-mounted substrates. The correct rate of inspection reached 99.7% in both the determination methods, which clearly indicates that proposed method may be useful in practice.

High Speed Oblique CT System for Solder Bump Inspection

The high-density LSI packages such as BGA (ball grid array) and CSP (chip scale package) are widely used in the electrical products. Solder bump is used as an electrical junction of these packages, and they cannot be observed from outside. X- ray fluoroscopy is used as inspection method. It cannot evaluate the shape of solder bump correctly because information is compressed along the ray. The oblique CT is considered as a method for accurately examining the shape of the solder bump. Conventional oblique CT still has the speed and mechanical constraint, and it cannot be introduced into the soldering line. In this paper, we propose the novel oblique CT system that can non- destructively obtain the 3D shape of solder bump at a high-speed. This system obtains the projection images from various directions using the rotational transfer of flat panel detector and the fixed mounted open-type X-ray generator that has a wide radiation angle, and reconstructs 3D image using the 3D FBP (Filtered Back Projection) method. In addition, we have developed the reconstruction acceleration unit for oblique CT, and thus the 3D image is obtained in the real time. In our experiments, we evaluated the solder joints of BGA mounted substrate. The result demonstrated that the proposed system obtained the information that was able to determine the good or defective situation in soldering. This system is the worlds first CT system, which can be introduced into the soldering line, and it is operated by more than 20 domestic and foreign factories now.

Automated Solder Inspection Method by Means of X-ray Oblique Computed Tomography

High-density LSI packages such as ball grid array (BGA) are being utilised in the car electronics and communications infrastructure products. These products require a high-speed and reliable inspection technique for their solder joints. In this paper, we propose an automated X-ray inspection technique for BGA mounted substrate based on oblique computed tomography (OCT). Automated inspection consists of OCT capturing, position adjustment, bump extraction, character extraction and judgment. We proposed five characteristic features related to the bump shape. Moreover, by combining the characteristic features using artificial neural network, the condition of a solder bump was determined. In the experiments, we evaluate these techniques using actual BGA-mounted substrate. As a result, the correct rate of judgment reached 99.7%, which shows the clearly indicates that our method may be useful in the practice.

Development of an automated X-ray inspection method for microsolder bumps

BGA, CSP, and flip-chip packages are widely used in printed circuit boards. These packages use an array of solder bumps as the electrical junction. To reduce the failures in manufacturing and after long-term use, solder bump inspection is strongly required for quality control. In this paper, we propose an automated inspection method for microsolder bumps using an X-ray image. The thickness, area, volume, and void of the solder bumps were automatically inspected by this method. We introduced some correction techniques to reduce the effects of variation in the X-ray intensity and the spatial nonuniformity in the image. In this experiment, we evaluated accuracy and repeatability. The results demonstrated that the accuracy and repeatability met the requirement for online inspection. In conclusion, our automated method for inspecting microsolder bumps may be useful in practice.

Development of high-speed X-ray CT inspection system using X-ray line sensor

The recent progress in surface mount technology has highlighted an urgent demand for a higher performance level of inspection technology. X-ray inspection is one of the most suitable systems for substituting the conventional automated optical inspection system. In particular, X-ray computed tomography (CT) inspection provides precise inspection as it can obtain three-dimensional data and can distinguish the features on the top side of a double-sided printed circuit board (PCB) from those on the bottom side. However, X-ray inspection systems are not in common use in the surface mount production line due to their complex image capturing mechanism, which requires a longer inspection time. Taking this limitation into consideration, we developed a simple mechanism utilizing an X-ray line sensor to obtain CT images of a wide area at a faster rate. We term this system as linear CT. In this paper, we explain the image capturing mechanism of linear CT and report that this mechanism can generate cross-sectional images of sufficiently high quality for precise inspection.

DEVELOPMENT OF AN AUTOMATED SOLDER INSPECTION SYSTEM WITH NEURAL NETWORK USING OBLIQUE COMPUTED TOMOGRAPHY

The high density LSI packages such as BGA is being utilized in the car electronics and communications infrastructure products. These products require a high-speed and reliable inspection technique for their solder joints. In this paper, an automated X-ray inspection system for BGA mounted substrate based on oblique computed tomography are proposed. Automated inspection consisted of OCT capturing, position adjustment, bump extraction, character extraction and judgment. Five characteristic features related to the bump shape are introduced. And by combining the characteristic features using artificial neural network, the condition of solder bump was judged. In the experiments, these techniques were evaluated using actual BGA mounted substrate. As a result, the correct rate of judgment reached 99.7%, which shows the clear evidence that proposed techniques may be useful in the practice.Copyright