Issue link: https://iconnect007.uberflip.com/i/505968
18 SMT Magazine • May 2015 Feature mINIaTURIzaTION WITH THE HELP OF REDUCED COmPONENT-TO-COmPONENT SPaCING continues The PCB has different sections with various component spacing within the same compo- nent type, and with mixed component types, the spacing ranges between 100–200 µm. Due to the narrow component and pad spacing, solder mask between the pads is only feasible down to 150 µm pad-to-pad spacing. The main focus on this study have been to reduce the component spacing between passive parts since this is the main challenge due to sol- der bridges. Passive components next to CSPs, and CSPs next to CSPs, present minor assembly issues and rework concerns. Solder Paste Selection A type 4 SAC 305 (Sn96.5Ag3Cu0.5) halo- gen-free solder paste was used for all our studies related to miniaturized assembly technologies. The selection of solder paste was done through extensive evaluations on printability, voiding, slumping, solder balling, wetting and SIR (sur- face insulation resistance). For all technologies included on the miniaturized test vehicle the common challenge is solder paste printing and the 0.3 mm pitch CSP and 01005 locations use very similar apertures sizes. assembly Details Assembly trials were conducted under con- trolled production environment. During the as- sembly trials, dip fluxing was used for the PoP and 0.3 mm pitch CSPs that were mounted on the board as well. All components were mount- ed at high speed to simulate a true production environment. Paste Printing and Solder Paste Inspection A standard paste printing process was used with a 3 mil (75 µm) and 4 mil (100 µm) thick laser-cut stencil, which was electro-polished from a local supplier in Asia where most of the production of miniaturized products would be produced. Automated solder paste inspection was done on all locations to collect data and automatic stencil cleaning was done after each print mainly due to the 01005 and 0.3 mm pitch Table 1: Cp and Cpk with 3 mil and 4 mil stencil thickness. Figure 6: Volume Cp, Cpk, pp and ppk with 3 mil and 4 mil stencil thickness.