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June 2014 • SMT Magazine 61 THe TROuBLe WITH BgA SOLDeR JOInTS continues arTICLe even between different products in the same production site. Possible faults in intermetal- lic zones with sporadic contact failure are an essential threat and may lead to catastrophic consequences for critical applications in, for ex- ample, automotive electronics. Depending on the respective situation, appropriate test equip- ment technologies should be used. But which technologies meet these requirements best and is there an ultimate strategy for quality assur- ance per se? A Look Behind the Scenes Test and inspection systems have two key strategic objectives. On the one hand, all pro- duction process faults shall be found, and on the other hand, each system acts as a process sensor in the required control loop of qual- ity assurance. In practice, there are a number of different technologies available to meet this challenge; however, only a few are suitable for BGA solder joints. This is all the more true if an IPC-A-610-compliant production must be dem- onstrated. Modern 3D inspection systems are capa- ble of quantitatively measuring solder joints, whereas electrical test systems can only provide pass/fail information about the contact status. Table 2 lists the capabilities of various test/in- spection methods with respect to essential test criteria and technical features. Methods include AOI (automated optical inspection), MXI (man- ual X-ray inspection), AXI (automated X-ray inspection), AXOI (automated X-ray/AOI in- spection), boundary scan (IEEE1149.x), ICT (in- circuit test) and FPT (flying probe test). It quickly becomes evident that no universal solution is available. Each technology aims at certain defect classes. MXI systems offer high- resolution in the lower micron range and thus are capable of detecting all mechanical defects. However, they are pure off-line machines and Table 1: overview of typical fault categories of bGa solder joints.