May, 2021
www.us-tech.com Continued from previous page
Meeting EV Safety and Quality Demands.... The current evaluation computers use
soldering flux. Automated optical inspection (AOI) does
not detect voids. Functional testing can also yield positive test results, even though the solder joint is not thermally stable, due to voids. An X-ray inspection is the only method that shows the position and distribution of voids, with 2D, 2.5D and 3D offering various inspection options. In 2D inspection, the X-ray beam strikes
perpendicular to the solder joint and pro- vides a direct measurement of the size of voids. The inspection is completed quickly and components are exposed to low levels of radiation. But, its effectiveness is limited when it comes to shadowing by absorbent material on the under- side of the PCB.
With 2.5D X-ray inspection,
the images of the solder joint are taken at an oblique angle to the PCB. The inspection position is selected so there is no shadowing. The inspection is completed very quickly and again components are only exposed to low levels of radiation. In 3D X-ray inspection, 2.5D
images of a single plane are taken at different angles and combined into a composite digital model. The higher the number of images, the better the quality of the 3D slices. This produces very high- resolution images and results in no shadowing. However, inspec- tion time increases with more images and components are exposed to higher levels of radia- tion.
Mixing the best of each of
these methods allows for target- ed optimization of the perform- ance and coverage of X-ray inspection. Inspection systems like
Viscom’s X7056-II 3D AOI/AXI offer combined automated optical and X-ray inspection. The com- bined solution optimizes inspec- tion coverage and speed, while minimizing radiation exposure.
Faster Inline Inspection A number of conditions need
to be met so that the results of the X-ray inspection meet quality requirements and can be used to improve processes. The meas- ured values have to be repro- ducible and accurate, their meas- uring resolution must be of a suf- ficiently high quality and they have to be verifiable. The suitability of the meas-
uring system is verified by means of a measuring system analysis (MSA) performed on a certified calibration material. Viscom has achieved significant advances in terms of measuring accuracy and speed. The integrated flat panel
detectors (FPD) deliver meas- ured values that are 3.2 times more stable than the correspon- ding image intensifiers previous- ly used. X-ray inspection was too slow for inline process monitor- ing prior to this.
the graphics processor (GPU) as well as the main processor (CPU) to execute calculations in parallel, considerably accelerating the process. Such progress makes fully automat- ed inline X-ray systems with shorter expo- sure times and faster analyses feasible even for high-quality 3D inspection. In addition, a higher sensor resolution
enables finer sampling rates, resulting in a very high resolution of up to 6 µm in 3D inspection. Improved algorithms make it pos- sible to analyze the image data in the pixel range, as well as in the sub-pixel range. The algorithms ensure that any interfering sig- nals are suppressed and the measuring sig- nals can be evaluated without interference.
Page 57
In addition, the effort involved in pro-
gramming X-ray inspections is significantly reduced, due to the improved algorithms. Configuring threshold and tolerance values is then much easier. Tegular grayscale value calibrations and
corrections ensure better reproducibility. The FPD can also be moved by a wear-free x/y- axis system, enabling 3D evaluations at dif- ferent stages of quality and throughput.
Improving Measurements 2D AOI methods are suitable for meas-
uring offset (according to IPC Class 3) and twisting. 3D AOI methods are suitable for simplifying the identification of component Continued on page 64
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