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June 2015 • SMT Magazine 31 In-LIne SOLDeR PeneTRATIOn TeSTInG WITH 3D X-RAy InSPeCTIOn continues station. In addition to determining the solder penetration, the system is also capable of calcu- lating the solder volume (mm³). In order to do this, N-slices with the thickness "d" are gener- ated between the solder and component side as before for determining the penetration, and the individual volume is calculated for each slice. Finally, the sum of the volumes of all the slices gives the total volume. In the case of a THR solder joint, the solder source side and solder target side are reversed. The acceptance criteria remain the same, how - ever. Inspection of THR solder joints is therefore easily possible. However, due to the degassing of the flux of the solder paste during the soldering process, in the case of THR solder joints there is often a relatively high proportion of air pockets within the solder joint. This is where the use of a 3D X-ray system is predestined to be able to detect breaks in the solder penetration. In order to set the parameters for the THT test function, only the corresponding connec - tors need be selected; the X-ray images (slices) are then displayed precisely above the AOI im- age. The parameters for the test function are then set using a few slide controls in order to enter the geometry of the THT solder joint and the necessary grey-scale value thresholds. This demonstrates another advantage of 3D X-ray technology: the solder joints are always shown in normalised plan view. This means that a sin - gle component library can be used. In addition, an integrated debugging statistics tool helps programmers to compare measured values from N-module inspections with each other and to optimise measurement thresholds. All the X-ray images required for the 3D re - construction (oblique radiation images) are cap- tured in motion (scanned) and computed in real time (reconstructed). This scanning image cap- ture is 3–4 times faster than in systems with pla- nar stop-and-go image capture technology. As a result, large assemblies with numerous connec- tors can also be inspected within the clock cycle. Summary To test the solder joints of THT/THR connec- tors, an in-depth look is necessary in order to ensure that it is not just "the tip of the iceberg" that is considered. A pure AOI system is not suf- ficient for fault finding if IPC guidelines are to be met. 3D X-ray technology enables conclusions to be drawn about the solder penetration and the solder volume, among other things, includ- ing a precise assessment of these criteria, while at the same time, meeting the high demands of the production line cycle. SMT Figure 5: left: schematic representation of the n-sectional planes. centre: Slice on the solder side. Right: Slice at 50%. Andreas Türk is division manager for Automatic X-ray inspection Systems at göpel electronic. Feature

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