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16 SMT Magazine • May 2015 Feature mINIaTURIzaTION WITH THE HELP OF REDUCED COmPONENT-TO-COmPONENT SPaCING continues Test Vehicles and materials The process development and factory quali- fication test vehicle for miniaturized assembly technologies (Figure 4) is designed to be similar to a cellular phone using the IPC drop test ve- hicle JESD22-B111 as a baseline. The company test vehicle is continuously being upgraded based on new findings and technologies; it also serves as a verification vehicle for the "Printed Circuit Board Design Guidelines." The PCB panel is 132 mm x 77 mm (Figure 4) and it is made with three identical sections. The surface finish for this board is organic surface preservative (OSP). One side of the PCB is using solder mask defined (SMD) pads and the other side is using non-solder mask defined (NSMD) pads for the active components. The PCB has four layers using halogen-free resin-coated cop- per (RCC) in the outer layers to enable a better quality for the microvia drilling. Halogen-free FR-4 is used in the inner layers. The total PCB thickness is 0.788 mm (Figure 4). Due to the high I/O count, small pad sizes and tight spacing the PCB design is very chal- lenging in many aspects. • ½ oz (20 µm copper), around 33–34 µm (after plating) • 50 µm copper/copper spacing (inner and outer layers) • 50 µm solder mask slivers • 25–40 µm solder mask registration tolerance • 60 µm uvias • 0.2 mm uvia capture pads in outer and inner layers • No silkscreen is used to prevent screen printing issues. Typical silkscreen thickness is around 20 µm (Figure 5) Copper-filled microvias are used based on previous studies on 0.3–0.4 mm pitch CSPs where we see better screen printing results since the solder paste has a bigger area to ad- here against. Furthermore, the so-called mi- crovia induced voids more or less disappear on bumped connections such as CSPs and BGAs. The negative impact of copper filled microvias is increased PCB price. The PCB includes a number of different component types, including: • Passive parts: 01005, 0201, 0402, 0603 and 0805 • Active parts: 0.4 mm pitch PoP, 0.4 mm pitch CSP and 0.3 mm pitch CSP Figure 4: Miniaturized assembly test vehicle. Figure 5: Silkscreen on top of solder mask.