Masatoshi Tsuzaka

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.

A depth-dose measuring device using a multichannel scintillating fiber array for electron beam therapy

The development of a new depth-dose measuring device for electron beam therapy is described. The device employs plastic scintillating fiber detectors inserted in a polymethylmethacrylate (PMMA) phantom in line along an incident electron beam. Output photons from a fiber, the number of which is proportional to the absorbed dose at each depth of the phantom, were converted to an electric signal with a photodiode. Each signal from the photodiode was transmitted to a personal computer through a multichannel analog-digital converter, and was processed to draw a depth-dose curve on the computer display. A depth-dose curve could be obtained in a measuring time of 5 s for each incident electron beam with an energy range between 4 and 21 MeV. The mean electron energies estimated using the curves and the depth-scaling factor for PMMA were consistent with those obtained from conventional depth-dose measurements using an ion chamber and a water phantom. The newly developed system, being simple and not time consuming, could be used routinely for quality assurance purposes in electron beam therapy.

Selective fallopian tube catheterisation in female infertility: clinical results and absorbed radiation dose

Clinical results of fluoroscopic fallopian tube catheterisation and absorbed radiation doses during the procedure were evaluated in 30 infertility patients with unilateral or bilateral tubal obstruction documented on hysterosalpingography. The staged technique consisted of contrast injection through an intraurine catheter with a vacuum cup device, ostial salpingography with the wedged catheter, and selective salpingography with a coaxial microcatheter. Of 45 fallopian tubes examined, 35 (78%) were demonstrated by the procedure, and at least one tube was newly demonstrated in 26 patients (87%). Six of these patients conceived spontaneously in the follow-up perod of 1–11 months. Four pregnancies were intraurine and 2 were ectopic. This technique provided accurate and detailed information in the diagnosis and treatment of tubal obstruction in infertility patients. The absorbed radiation dose to the ovary in the average standardised procedure was estimated to be 0.9 cGy. Further improvement in the X-ray equipment and technique is required to reduce the radiation dose.

A scintillating fiber beam-energy monitor for electron beam therapy.

A new type of beam-energy monitor is described, which has been developed to check the energies of electron beams from radiotherapy accelerators. The monitor consists of a pair of scintillating fibers and photodiode read-out circuits that measure the energy dependence of electron transmission through a wedge-shaped absorber. A linear energy response and 1% accuracy for energy constancy measurements are attained with the monitor. The monitor having advantages of simple mechanical and electronic constructions, small size, and low cost is suitable for practical use as a portable device.

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.

Evaluation of the partial flip angle spin echo method to improve non-uniformity in T1-weighted imaging with the 3-tesla MRI

The higher signal-to-noise ratio (SNR) of 3-Tesla magnetic resonance imaging (3T MRI) contributes to an improvement in the spatial and temporal resolution. However, T1-weighted images of the brain obtained by the spin-echo (SE) method using 3T MRI are unsuitable for clinical use because of the inhomogeneity of the radio frequency (RF) field B1 non-uniformity. And it is clear by SE method. In addition, the prolongation of the longitudinal relaxation time (T1) of most tissues leads to a decrease in the T1 contrast. Therefore, many hospitals that utilize 3TMRI use the GRE method instead of the SE method in order to obtain an adequate T1 contrast, as can be obtained using FLASH (fast low angle shot), and high uniformity of images. Further, many studies have been performed to improve the non uniformity using techniques such as spatial presaturation. However, when filters are used, the high intensity of the influence in susceptible regions, signal deficits, and original contrast are lost, and a distortion can be clearly observed when the GRE method is used. Therefore, we obtained the T1-weighted images by using the partial flip angle SE method instead of the GRE method or SE method. We attempted to improve the image non-uniformity by using the partial flip angle SE method. Using this method, we could improve the image uniformity and also realize an adequate T1 contrast. As a result, the uniformity was found to improve by 6% and it became 82.6% at 110°. These results indicate that the use of the partial flip angle SE method is effective for obtaining adequate uniformity in the T1-weighted images of the brain.

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