Reliability of Ultra-Thin Embedded Silicon Fan-Out (eSiFO) Package Directly Assembled on PCB for Mobile Applications

In this paper, ultra-thin eSiFO packages with body thickness of 150 µm were presented and the reliability were comprehensively studied, with an emphasis on temperature cycling (TC) and drop test reliability. The test vehicle was designed in two different sizes: a 3×3 mm package with a single 1.4×1.4 mm embedded die and a 9×9 mm package with a single 7×7 mm embedded die. Several electrical measurement structures, such as daisy chains, Kelvin test units and leakage current test units were built in the test vehicles. Manufacturing process of the ultra-thin test vehicles were described at the first, then the package level reliability and board level reliability were also studied. The possible failure modes were determined by electrical test and cross-section observation. Experimental results show that ultra-thin eSiFO packages have a stable manufacturing process, good package level reliability and board level drop reliability acceptable for mobile applications regardless of the package size. Temperature cycling on board experiments show that ultra-thin eSiFO package has a similar solder joint fatigue life to standard WLCSPs and typical eWLBs. The results of this work offer an important reference for reliability of embedded, fan-out packages and other ultra-thin WLCSPs.