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62 SMT Magazine • June 2014 can't be used for automated operation. Quite the opposite is valid for AXI systems. They are in-line-capable in principle and 3D machines can qualify according to IPC-A-610. Unfortu- nately, they have a lower resolution, so they have problems with detection of poor bonding in intermetallic zones. AXOI devices combine AXI and AOI into one system. So they are ca- pable of putting down BGA solder joint defects to incorrectly placed chips. In the field of electrical tests, physical con- tactability of traces plays an essential role for the applicability of those technologies. High-density BGA assemblies with completely embedded trac- es push long-term reliable test methods like ICT and FPT into an increasingly marginal role. The boundary scan test method is known as a ground- breaking alternative: it is standardised according to IEEE1149.x [2] and operates adapterless. Based on the already discussed production test requirements for complex BGA assemblies, two technologies crystallise: X-ray systems (AXI and AXOI) and boundary scan systems for the electrical counterpart. Both methods will be discussed in more detail in the following. A complementary situation is assumed, because an electrical test yields no information on the mechanical status of the solder joint and an au- tomated inspection of the solder joint doesn't guarantee an electrically perfect signal trans- mission. Maxing Out the Potential of X-Ray Even if in principle X-ray technology is capable of seeing the balls by taking a look through the BGA, this is a required technical prerequisite. The effective customer benefit is primarily defined through the technological THe TROuBLe WITH BgA SOLDeR JOInTS continues arTICLe Table 2: performance of various technologies regarding identification of bGa faults.