Flip chip interconnect systems using wire stud bumps and lead freesolder

摘要

This research focuses on flip chip interconnect systems consistingof wire stud bumps and solder alloy. Conventional gold (Au) wire studbumps and new copper (Cu) wire stud bumps were formed on the chip bywire bumping. Cu wire studs were bumped by controlling the ramp ofultrasonic power to eliminate the occurrence of under-pad chip crackswhich tend to occur with high strength bonding wire. Lead free96Sn3.5Ag0.5Cu alloy was used to interconnect the wire studs and printedcircuit board. A comparison is made with conventional eutectic 63Sn37Pballoy and 60In40Pb alloy. A more stable solder connection was createdwhen Cu wire stud bumps were used, compared with Au wire stud bumps. Theimproved stability is due to reduced intermetallic compound formationwith the solder alloy. Test vehicles were assembled with two differentDirect Chip Attachment (DCA) processes. When a conventional flip chipassembly and reflow was used, the lead free test vehicles exhibitedprocess failure. On the other hand, when solder reflow and underfillcure were performed at the same time by using a high accuracy flip chipbonder, the reliability of lead free test vehicles in thermal shockimproved