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Flip chip interconnection to organic substrates. A comparison between adhesive bonding and soldering

: Jung, E.; Aschenbrenner, R.; Zakel, E.; Reichl, H.

International Society for Hybrid Microelectronics -ISHM-:
10th European Microelectronics Conference 1995. Proceedings
Kopenhagen, 1995
ISBN: 87-985510-1-9
European Microelectronics Conference <10, 1995, Kopenhagen>
Fraunhofer IZM ()
adhesive bonding; flipchip; mechanical bumping; reflow soldering

Over the last years an increasing number of flip chip (FC) interconnection technologies have emerged. While flip chip assembly offers many advantages compared to conventional packaging techniques, several aspects prevent this technology from entering the high volume market. Among these are the availability of bumped chips and the costs for the substrates with matching coefficient of thermal expansion (CTE) to the chip (i.e. AlN substrates) in order to maintain a high reliability. FC soldering of bumped chips on organic PWB and subsequent underfilling using a low viscosity, particle-filled epoxy material was shown to yield reliable interconnections. For this paper, electrolessly Ni-Au plated chips were mechanically bumped with PbSn2 bumps using a semiautomatic wirebonder. They were subsequently soldered on an organic substrate (FR4) with PbSn60 bumped pads and underfilled. Another possibility is the use of chips with gold stud bumps, which are bonded to the FR4 substrate by using a nonc onductive adhesive foil. During the bonding the bumps pierce through the foil and make the electrical contact while the adhesive supplies the mechanical stability. Moreover, the adhesive fills the gap between chip and substrate, relieving the bumps of the mechanical stress resulting from the different CTE's. The reliability of the connections produced by using these techniques is the subject of the studies presented in this paper.