Can AXI Meet Zero Defect Quality Standards?
December 31, 1969 |Estimated reading time: 4 minutes
AXI is a standard quality control tool for inspection of hidden solder structures. Tobias Neubrand, Ph.D., GE Sensing & Inspection Technologies GmbH - phoenix|x-ray Systems + Services Inc., explains the capabilities necessary on X-ray systems to meet current and future zero-defect quality standards.
Figure 1. Open BGA solder joint (center of image).
For ball grid array (BGA), chipscale package (CSP), and flip-chip applications, automated X-ray inspection (AXI) is an accepted and standardized quality-control procedure. Its utility increases for inspection of hidden characteristics of other SMD solder joints such as quad flat pack (QFP)- and quad flat pack no-lead (QFN)-elements. Any defects that show a noticeable influence on the shape of the solder joint can be detected by X-ray analysis (Figure 1).
To ensure quality-sensitive electronic assemblies meet actual and future zero defect quality requirements, the inspection strategy for a minimized escape and pseudo-defect (false call) rate should determine the inspection time, not the line throughput. With common in-line AXI, the inspection depth is normally determined by the SMT line’s throughput. Principally, X-ray inspection takes much more time than automated optical inspection (AOI), and the higher the defect coverage; the more inspection time is required.
Efficient CAD Programming and Minimized Set Up TimeAXI inspection times can be reduced with more efficient software rather than reducing defect coverage.* To minimize programming time, AXI software can use CAD import of component and pad information instead of more complicated and less exact view-based programming. The operator links specific inspection strategies from a library to each pad type such as BGA, QFP, PTH, etc; the software can automatically create the inspection views. CAD-based programming means inspection programs can be generated off-line and are portable to all compatible AXI systems. The programs’ portability means that inspection regimes can be consistent within a facility with multiple AXI systems, or externally to multi-facility environments or partners. This targets reduced time at inspection and associated costs. Benefits include a minimized pseudo defect and escape rate for highest reliability of electronic products, and reduced inspection times.
Figure 2. Easy CAD programming.Filters can be used to extract the required information out of customized data formats. Programming software that works with CAD uses pad-based information (Figure 2). Operators link specific inspection strategies to each type of pad. Different pad types usually require different strategies. If a strategy needs to be changed in an existing program, this step can be streamlined by marking all pads of the same type, making the change all at once and lowering the chances of operator-introduced errors. After import of the data, CAD-based software automatically generates inspection views.
CAD-based software provides a live overlay of the X-ray image and the CAD information. This overlay is available even for oblique views (Figure 3). The pad ID is visible at any time. Additionally, pad-specific inspection results are accessible. The overlay technique is convenient for the operator, offering perfect orientation at any time. This enables reliable identification of a specific joint or a specific group of joints on a board, which, with thousands of solder joints, can otherwise be time consuming.
Figure 3. High-resolution X-ray evaluation of some gullwing solder joints with live CAD overlay in ovhm and visible inspection results.
Defect CoverageQuality comes first in printed circuit board assembly. To maintain the required level of quality on the SMT line, manufacturers often require calibrated high-precision off-line AXI systems**. When selecting an AXI system, look for CAD-based programming, small field of views (FOV) with micrometer resolution, 360° rotation, and oblique viewing up to 70°. Inspection programs should be intuitive so more, less-skilled operators can be employed. With CAD-based programming, the component's CAD data is read into the X-ray system and laid over the image, allowing users to have the complete sample data available at all times, even when using oblique views (tilt and rotation).
3D Auto-referencing for Positioning Accuracy A local 3D height and distortion referencing method (Figure 4) on X-ray inspection systems offers high precision by measuring as many fiducials as required. By using X-rays instead of optical triangulation sensors, the 3D method does not depend on the quality and reflectivity of circuit board surfaces. The image chain is calibrated and any
Figure 4. Visualization of board distortion.distortion is automatically compensated. The combination of all these efforts allows a high positioning accuracy even at oblique viewing (70°) and rotation (360°).
Ful CT and µAXI InspectionA high-resolution automated X-ray inspection system is most suitable for failure analysis (FA) in the semiconductor and electronics industry. Total magnification greater than 23,000× (without software zoom) and oblique angle views of up to 70° at any position and 360° rotation around any point of the entire inspection area suit this manufacturing process and the component sizes and densities seen in semiconductor and electronics products. When selecting a machine, also consider the board size and weight limits of the inspection chamber, referenced against the typical assembly you are producing.
A high-resolution X-ray source is also essential for full 3D computed tomography (CT). Especially for smaller devices with complex internal structures, X-ray CT extends the possibilities of defect analysis and can partly replace destructive methods in a time-saving way.
Conclusion Future zero-defect quality standards will require highest defect coverage and minimized false call rates, outstanding image quality, highest magnification, maximized position accuracy, easy CAD-based off-line programming, full program portability, and CAD-data overlay even in rotated and oblique live views.
Figure 5. Computed tomography: 3D visualization of the internal structure of a ceramic SMD IC.
* Data provided is from a phoenix|x-ray 180 kV/20W microme|x X-ray inspection system equipped with the x|act software platform.** Data provided is from the µAXI platform x|act from phoenix|x-ray.
Tobias Neubrand, Ph.D., 2-D product manager, GE Sensing & Inspection Technologies GmbH - phoenix|x-ray Systems + Services Inc., may be contacted at +49 5031 172 133; Tobias.Neubrand@ge.com; www.gesensinginspection.com; www.phoenix-xray.com.