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38 The PCB Magazine • October 2014 f e a t u r e Abstract The next generation of smartphones will demand very thin multilayer boards to reduce product thickness again. This paper shows three different manufacturing approaches which can be used for very thin, any-layer build-ups. The technological approaches are compared on reliability level—the any-layer copper filled microvia technology which is to be considered as state of-the-art technology for high end phones and the ALIVH-C/G technol- ogy that is well established in Japan. A test ve- hicle design featuring test coupons for compre- hensive reliability test series has been defined as target application for investigation. The applied test vehicle build-ups comprise an eight-layer build-up with total board thickness below 500 µm. The first test vehicle is based on an any-lay- er HDI build-up including copper filled stacked microvia structures, the second test vehicle fea- tures a 1+6+1 ALIVH-C build-up comprising an outer HDI prepreg layer, while the third test ve- hicle is built in ALIVH-G technology featuring a full ALIVH build-up. The influence of the applied manufacturing technology on the reliability performance of thin PCBs is evaluated based on these three test vehicle build-ups. To cover the behavior during SMD compo- nent assembly the produced samples are sub- jected to reflow sensitivity testing applying a lead-free reflow profile with a peak temperature of +260°C. Failure occurrence and the observed failure modes are evaluated and compared. In parallel, a temperature cycling test is con- ducted on the test vehicles in a temperature range between -40°C and +125°C in order to evaluate the thermo mechanical reliability of the test vehicles with regard to the manufactur- ing technology. In order to characterize the reliability as- pects influenced by electrochemical migration phenomenon the different samples are subject- by Thomas Krivec, Gerhard Schmid, Martin Fischeneder, Gerhard Stoiber at&s austria Thin PCBs for Smartphones: Technology & Reliability Considerations

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