New-Tech Europe | September 2016 | Digital Edition

Figure 3. Redistribution Layer (RDL) WLCSP

temperature operating life testing (HTOL), and un-biased highly accelerated stress testing (UHAST). In addition to thermo-mechanical induced stress testing, mechanical tests such as drop and bend testing are also carried out. HTS testing is performed to determine the effect of long-term storage on devices at elevated temperatures without any electrical stresses applied. This test assesses the long- term reliability of devices under high temperature conditions. The typical test conditions are 150°C and/ or 175°C for 1000 hours. This test consists of exposing the parts at the specified ambient temperature for a specified amount of time. RESOURCES For further information on healthcare applications, visit our site.

Figure 5. Pad Type

thinner board results in smaller shear stress range, creep shear strain range, and creep strain energy density range in the solder joints under the thermal loading. Hence, the thinner buildup board would lead to a longer thermal fatigue life for solder joints. Testing and Assessment In conjunctionwith the aforementioned variables, WLCSP reliability is assessed by subjecting the device to accelerated stress tests such as high temperature storage (HTS), highly accelerated stress testing (HAST), autoclave testing, temperature cycling, high

Figure 4. Pad Opening

depends on the required robustness of the populated system assembly. The

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