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42 The PCB Magazine • October 2014 THIN PCBS FOR SMARTPHONES continues Design and Stackup of Test Vehicles For the targeted rigid eight-layer PCB test ve- hicle, a test design used regularly for reliability tests and material qualification issues at AT&S was selected. The test vehicle comprises sev- eral coupons for electrical and reliability tests with an eight-layer build-up. With regard to the defined production technologies slight modi- fication within the design of the single part numbers had to be made, however great care was taken to assure the comparability of the HDI and ALIVH test vehicles. Figure 3 shows the built test board and the corresponding test coupons used for the further tests within the re- ported work. Stackup and Applied Material For the reported work, three different test vehicles with different build-up approaches have been defined. As Table 1 shows there is one HDI build-up, one full ALIVH build-up (ALIVH- G) and an ALIVH-C build-up where layers 2–7 are manufactured in ALIVH technology and the two outer layers are then in a subsequent process step added in HDI technology. The ex- pected thickness column shows that thickness value for the board as it is calculated during the PCB design stage. Since the target applications this study is based on are from the mobile devices segment all used dielectric materials have been chosen figure 3: test vehicle design and corresponding test coupons. table 1: built test vehicles and expected total board thickness.