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June 2014 • SMT Magazine 63 THe TROuBLe WITH BgA SOLDeR JOInTS continues arTICLe device concept. In modern SMT production en- vironments, X-ray systems are deployed in-line or as a standalone solution to perform fully au- tomated X-ray inspection. Also the use of high- resolution manual or semi-automated X-ray de- vices (MXI) for sample analysis is widespread. In sum, AXI systems for use with BGA as- semblies in SMT production lines must meet some basic criteria: • Full inspection according to IPC-A-610E • Low fault slip • Low false alarm rate • Throughput matching the beat rate of the production line (in-line operation) • Automated fault detection • Simple programme generation • Intuitive user interface • Support of statistical process control (SPC) Regarding BGA components, IPC-A-610E deals with criteria like solder ball offset, sol- der ball distance, solder ball form and voids in the solder joint. It is also associated with IPC- 7095B [3] , which specially deals with design and process development of BGAs. To check as- semblies according to the requirements of IPC- A-610, tomosynthesis-based 3D AXI systems such as GOEPEL's OptiCon X-Line 3D [4] are par- ticularly effective. Figure 3 shows a solder ball and its vision evaluation. The images illustrate a cut through the centre level of the BGA balls. The evaluation yields results like ball area, roundness of the ball, position of the ball and its grey level. Here, the X-ray technology demonstrates its strength, delivering real measurement values. X-ray im- ages show changes in the material itself, as well as changes in material density and thickness. Voids are just an additional criterion of BGA ball integrity. They arise, amongst other things, during the reflow process, when the flux of the figure 3: Measurement of good and poor solder joints. figure 2: optiCon X-Line 3D with integrated aoI option (aXoI).