February, 2020
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Page 117
Accurate and Fast Volumetric Inspection with Inline 3D AXI Continued from previous page
3D Image Reconstruction PCT technology provides high
resolution in both the horizontal and vertical directions. For each PCB image slice, the AXI system provides completely separated images of the top and bottom sides. Because there are separate images for each field of view (FOV). These images can be reconstructed and connected into one seamless 3D-constructed model. Automatic board warpage compensa- tion is performed while the image slices are taken. Robust warpage compensation
is an essential function for accurate height reconstruction. Usually, an inspection tool, such as a laser, is used and the inspection machine has to be manually programmed with the exact location on the PCB where sur- face height is to be measured. This results in additional programming time and program optimization, and warpage of the surface underneath a covered surface is unknown. Saki’s AXI system can automatically inspect the pad layer, measure warpage height, and automatically perform warpage compensation any- where on the product.
Head-in-Pillow Inspection Head-in-pillow is a defect of the
solder joint. which looks like a head pressed into a soft pillow. This is caused by the failure of the solder ball and the PCB pad to melt togeth- er and form a seamless mechanical connection during the reflow process. The solder joint will have electrical integrity, but will fail under mechan- ical and thermal stress. Defects have countless varia-
tions in shape and identifying defec- tive shapes is very difficult in head- in-pillow inspection. 3D inspection is focused on recognizing fine shape deviations of the solder and then detecting an abnormality by compar- ing it with an ideal shape. Deep analysis of the solder shape under the BGA requires many measure- ments of various parameters related to the area of slices through the sol- der balls, such as circularity, volume, etc. The ability to separate layers and collect volumetric data enables a 3D AXI system to conduct detailed inspection of such solder joints. Based on years of research from
collected customer data, Saki has been able to identify the deviations from and trends of what is considered acceptable solder ball shape. After defining the shapes, Saki created an inspection log that was turned into a new algorithm that takes AXI inspec- tion capabilities to the next level. The algorithm unifies the vari-
ous definitions of solder shape and incorporates them into one inspec- tion step. It uses shape detection capability knowledge and combines it with highly sensitive and accurate 3D volumetric data to provide simple and easy parameter setting. This provides the ability to define the cor- rect inspection parameters quickly and easily. The number of escapes, or false
passes, during production is a signif- icant factor in judging inspection quality. An escape is a defect that is not
discovered during test.
Unfortunately, that defect is often overlooked and found by the cus- tomer when something fails. Having
See at IPC APEX, Booth 1800
too many escapes is very costly to the assembly process in manufacturing time and money. If the defect is found during pro-
duction, repair or replacement of the part is possible, but this slows down the line or the line must be stopped. Throughput and yield are decreased. The later in the process that a defect
is found, the more difficult and costly it is to fix it or adjust the line. Saki’s 3XiM110 AXI system produces such high inspection quality and reliabili- ty that the inspection process can result in zero escapes.
Environmental Concerns In any X-ray system, strict
adherence to control and use of the X-rays is critical to the machine’s operation. With reduction of X-ray exposure as its focus, Saki imple- mented a brand-new, closed X-ray tube. The 3Xi-M110’s tube has a pulse mode capability to switch the X-ray on and off during high speeds. An X-ray reduction of 70 per-
cent is possible by powering the X- ray only at the moment of image cap- turing and powering it off while the board is being loaded. Conventional closed tubes must be turned on and off periodically, even when kept as a spare part, to prevent the deteriora- tion of the tube. This is a costly and time-consuming operation. When using the new 3XI’s X-ray
Sliced images by tomosynthesis and planar computed tomography. Continued on next page
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