Advances in X-Ray Inspection For Electronics, Part 3: Microelectronics
July 21, 2016
A Better Image For Demanding Applications
As new technologies emerge, they push x-ray systems to evolve and adopt new methods of imaging in difficult materials and locations. One of today's more prevalent and demanding areas that x-ray systems has been able to provide a solution is in microelectronics.
ENHANCING THE IMAGE CHAIN
The image chain consists of more than just the digital detector and the tube. It also includes the computer processing which captures the image data and the monitor itself that together determine image quality and permits you to view images in real-time.
When the frame rate is sufficient (30 to 60 fps), images can be viewed and manipulated live on a monitor. Typically, when greater quality is desired for an image, the frame is captured and processed by the computer to produce the desired results.
A more advanced development of the image chain allows processing images during the image stream, and as a result, all the images viewed on the monitor are enhanced. The distinction that occurs can be significant. For instance, when viewing a crack in a solder ball (Figure 1), instead of selecting images that appear to best show the crack and then processing those images, you can view an enhanced image of the crack in real-time, while the position of the sensor (or the specimen) is changed to provide multiple viewing angles.
Figure 1. Oblique view of BGA with 16bit DFP
Another high value tool for live image analysis is the μHDR (Figure 2 below) which averages the exposure of the overall image and shows the structure of the sample object.
Figure 2. μHDR images
CHALLENGES OF MICROELECTRONICS
All the advances of x-ray technology, described earlier, address the need to verify the quality of smaller and smaller 3D packages.
3D packaging is the general term that encompasses stacked components, 3D IC’s, Package-on-Package, System-in- Package, and many others. The primary driver of 3D Packaging is that the technology saves space by combining separate chips in a single package. The general expectation is that the stacked packages must be able to maintain or lower the Z-height of a package, requiring thinned die, low-level interconnection techniques such as Thru-Silicon Via (TSV), copper pillars, microbumps. These technologies promise increased system integration at a lower cost and reduced footprint.
All stacked packages have all the normal reliability concerns such as TSV void, bump uniformity, flip-chip solder reliability (see figure 8), package warpage and thermal stress.
Although most of these defects are difficult to detect due to the sub-micron size of defects or due to thinner and lower density materials, modern x-ray systems make it possible by combining 2D, µ3D scan or Micro3D Slicing methods.
A recommended x-ray system for microelectronics applications would have a Nanofocus x-ray tube with TXI feature and at least 16-bit digital flat panel detector with balanced spatial and contrast resolutions.
Additionally, the manipulation of the detector, the tube and the sample tray is important. If the tube and detector can be moved independently, it allows the operator to find the best possible signal-to-noise ratio at specific target power, magnification and reduces the risk of potential damage to sensitive devices.
Think you know what today's X-ray inspection for electronics can do? Read the full white paper on this topic, a free PDF download:
"Recent Advances in X-ray Inspection for Electronics Manufacturing"
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