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|Title: ||Under bump metallisation of fine pitch flip-chip using electroless nickel deposition|
|Authors: ||Liu, Changqing|
Hutt, David A.
Whalley, David C.
Conway, Paul P.
Mannan, Samjid H.
|Issue Date: ||2000|
|Publisher: ||© IEEE|
|Citation: ||LIU, C....et al., 2000. Under bump metallisation of fine pitch flip-chip using electroless nickel deposition. IN: International Symposium on Electronic Materials and Packaging, (EMAP 2000), Nov. 30- Dec. 2, Hong Kong, pp. 64-71.|
|Abstract: ||For solder based flip-chip assembly, the deposition of
an under bump metallisation (UBM) layer onto the surface
of the AI bondpads of the die is the first step in the wafer
bumping process. The UBM is necessary, as the fragile AI
pad has a tenacious oxide layer that cannot be soldered
without the use of strong fluxes and a barrier layer is
required to prevent dissolution of the bondpad into the
solder during reflow. The requirements of the UBM are
therefore to provide a solder wettable surface and to
protect the underlying A1 bondpad during and after
assembly. In addition, the UBM deposition process itself
must remove any oxide layers on the bondpads to ensure a
low resistance interface between the pad and the UBM.
This paper reports an investigation of the electroless nickel
deposition process for the under bump metallisation of
wafers that are subsequently to be bumped using solder
paste printing. In particular this work has extended the
process from previous trials on 225pm pitch devices to
wafers including die with sub lOOpm pitch bondpads. As
part of this work, the effect of the various pre-treatment
etching processes and zincate activation on the quality of
the final electroless nickel bump has been investigated.
The use of SEM examination of samples at each stage of
the bumping process has been used to aid a detailed
understanding of the activation mechanisms and to
determine their effects on the electroless nickel bump
morphology. In addition shear testing of bumps has been
used to determine the best pre-treatment regime to ensure
good adhesion of the electroless nickel to the bondpad.
Finally, electrical resistance measurements of bumped die
have been used to confirm that the pre-treatment
procedures are producing a low resistance interface
between the AI and electroless nickel.|
|Description: ||This is a conference paper and the definitive version is also available at: http://ieeexplore.ieee.org. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.|
|Appears in Collections:||Conference Papers and Presentations (Mechanical, Electrical and Manufacturing Engineering)|
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