COMPONENT AND PRINTED WIRING BOARD FINISH EFFECTS ON QFN SOLDER JOINT FORMATION

摘要

Quad flat no-lead (QFN) packages have rapidly gained wide spread acceptance in numerous applications as the demand for lower profile electronic packaging solutions continues to rise. However, the growth of this package type has not come without challenges including primarily void formation in QFN solder joints. Proposed solutions to the voiding issue have focused on adjustments to the solder reflow process (profile, flux type, etc.) and board layout modifications. A factor that has not received as much study in the literature to date is the impact of component and printed wiring board finishes on QFN solder joint formation. Wettability, intermetallic formation, and residual solder volume of the formed joint are all important considerations in the creation of a reliable solder joint and are affected by the finishes present on the adjoining soldered pads. This study reviews the destructive analysis of solder joints formed between QFN packages with different lead finishes including electrolytic gold/electrolytic palladium/electrolytic nickel and immersion gold/electrolytic palladium/ electroless nickel, soldered to printed wiring boards with ENIG and ENEPIG plating using eutectic tin-lead solder. Solder joint and void formation are studied and effects related to finish type are identified and potential impacts on long-term solder joint reliability discussed.