Several electronic devices are installed in automobiles for use in safety- and performance-related control functions. Moreover, control of the vehicle by electronic devices supports driving and provides a comfortable environment.
In recent years, the growing complexity of safety-related functions like erroneous start suppression and driving automation function has affected the higher performance of the electronic devices that control those functions. From the environmental perspective, optimum control of the engine based on vehicle running condition and enhanced fuel combustion efficiency are also necessitated. These types of control are executed by electronic control units (ECU), also known as “car computers.”
While in operation, cars fitted with these electronic devices vibrate continuously and are also influenced by temperature variations due to the heat from the engine and road as well as atmospheric temperature. Normal operation is required even in such harsh environments. With higher reliability requirements, ECUs and other electronic devices are usually enclosed in cases, but this indicates it is not feasible to inspect the devices themselves from their external appearance. Therefore, non-destructive investigation using X-ray methods is necessitated. In this article, an example of observation of an ECU using an X-ray CT system is described.
Observation of Car Computers (ECU)
Different sensors are installed in automobiles to facilitate normal operation even in severe environments. ECUs contain several parts for reading information from sensors to optimize engine combustion efficiency, as well as to monitor and control the automobile’s attitude, tire air pressure, temperature, and other crucial conditions for ensuring safe travel. In order to achieve higher safety and traveling performance, the control components with higher performance and functions have been used.
The use of higher density components and stacked boards through space-saving is also being advanced to enable these devices to be installed in the limited space of the automobile. Earlier, components that would most certainly operate were used from the perspective of reliability, even when their performance was low; however, the frequent use of the recent high-performance, compact components has necessitated high surface mounting technology, even in solder joints with boards.
An X-ray fluoroscopy system has been used for a long time to assess reliability due to variations in usage conditions, even though dedicated inspection equipment is used in operation-related electrical current tests. Higher analytical accuracy can be achieved by using an X-ray CT system in these assessments. The Shimadzu microfocus X-ray CT system inspeXio SMX-225CT FPD HR is shown in Figure 1. An image of the external appearance of an ECU is shown in Figure 2. The fluoroscopic image of ECU taken using this system is shown in Figure 3.
Figure 1. Microfocus X-Ray CT system inspeXio SMX-225CT FPD HR.
Figure 2. Image of external appearance of ECU.
Figure 3. Fluoroscopic image of ECU.
It is possible to show the entire ECU in a single image since the receiving section of the inspeXio SMX-225CT FPD HR is provided with a 16-inch flat panel detector which offers a maximum large field-of-view of around 300 × 300 mm. This paves the way to check for damaged and missing terminals and components, as well as large bending of parts. It is also possible to observe the position of the board, thereby enabling checks to be done for contact between the ECU case and the board and parts.
By increasing the magnification ratio, it is also possible to observe the interior of parts and to observe the solder condition of joints in more detail. Figure 4 is a fluoroscopic image of the area surrounding an IC captured by magnification radiology. In this figure, the internal wiring in the solder joints and the IC can be observed. By further enlarging the solder joint area (Figure 5), voids in solder joints with the board can also be determined.
Figure 4. Fluoroscopic image of IC part.
Figure 5. Fluoroscopic image of solder joint.
Next, a CT image of the whole ECU was taken, and as illustrated in Figure 6, Multi Planar Reconstruction (MPR) images were generated. The MPR function arranges the recorded CT images in a virtual space and displays the images of arbitrary cross sections. As shown in Figure 6, the CT image (as seen in (1)), cross-sectional images orthogonal to (1) (as in (2) and (3)), as well as cross-sectional images from any arbitrary angle (as in (4)) can be displayed. As it is also possible to display the enlargements of the required section images, detailed checks and observation are possible.
In these MPR images, (1) shows a cross section close to the center of the ECU, and (2) and (3) are respectively the vertical and horizontal orthogonal sections from the section in (1). The board surface from the section in (2) is shown in (4). As shown in (5), it is also feasible to enlarge arbitrary section images. Since CT imaging displays higher density areas in white, electronic components, solder joints, and the wiring of the board appear whiter. Therefore, the absence or presence of parts and solder can be confirmed from this common image.
Figure 6. MPR images of ECU.
Using the 3D software VGSTUDIO MAX (Volume Graphics GmbH), a Volume Rendering (VR) of the CT image can be shown. It is also possible to observe the bending of terminals and parts, and the absence or presence of parts on the rear side of the board in 3D by inspecting a shape closer to that of the actual object. With partially enlarged CT imaging (Figure 7), it is also possible to verify the wiring and solder joints of terminals and small parts inside ICs.
Figure 7. Enlarged VR image of IC.
An enlarged VR image of connectors that connect automotive wiring is shown in Figure 8. Even if solder joints are used at various terminals, voids in the solder (if present) may combine and develop into cracks owing to the effects of thermal expansion and vibration.
Figure 8. Enlarged VR image of solder joints.
Using an optional function of VGSTUDIO MAX (Fig. 9), individual voids can also be visualized, and their volumes, positions, and surface areas can be measured. This feature can be used not only to check for the presence of voids but also to enhance production efficiency, for instance, enhancement of yield, by determining the condition of defects from different types of quantified information and by adjusting the reflow conditions accordingly.
Figure 9. Analysis of Voids in Solder.
As the X-ray CT system is a non-destructive technology, thermal shock tests, vibration tests, and other cycle tests can be performed with the same product and the internal state can be examined in each stage of the test. Furthermore, the number of tests and the number of units of each testing device can be reduced. In addition, as the X-ray CT system is effective in analyzing the destruction process and reducing the number of samples needed and development time, it is also useful for accelerating the work and reducing the cost.
The inspeXio SMX-225CT FPD HR allows inspection and analysis of assembled products without the need to disassemble. The feasibility to vary production conditions and compare products prior to and after different types of tests makes it useful in production processes and also in development processes.
Different types of analysis can be performed using software appropriate for the purpose, and applications include the analysis of product defects as well as the study of production processes and comparison of the same samples before and after tests.
This information has been sourced, reviewed and adapted from materials provided by Shimadzu Scientific Instruments.
For more information on this source, please visit Shimadzu Scientific Instruments.