An Evaluation of Gold and Copper Wire Bonds on Shear and Pull Testing

[+] Author and Article Information
S. Murali, Charles J. Vath

 ASM Technology Singapore, 2 Yishun Avenue 7, Singapore 768924, Singapore

N. Srikanth

 ASM Technology Singapore, 2 Yishun Avenue 7, Singapore 768924, Singaporesrikanth@asmpt.com

J. Electron. Packag 128(3), 192-201 (Nov 23, 2005) (10 pages) doi:10.1115/1.2229214 History: Received September 06, 2004; Revised November 23, 2005

In microelectronic packaging technology wire bonding is a common interconnect technique. The quality and reliability of wire bonds are generally evaluated by ball shear and stitch pull testing. From the load versus time and load versus tool tip displacement plots of the shear test, three regions can be observed. Region I primarily exhibits elastic-plastic deformation occur, while crack nucleate in region II which propagates in region III which finally ends in a catastrophic failure. Fractographs reveal in the case of gold ball bonds shows fracture occurs in Al bond pad metallization close to Au-Al intermetallics. In Cu ball bonds of 1, 2, and 4ml wire sizes also Al bond pad metallization cracks but penetrate deeper into the pad which indirectly shows that the bonding layer is stronger than that of gold ball bonds. Optical microscopic observation of the sheared copper bond surfaces reveal sticking of Al which provides qualitative information of the area of the bond between the ball bond and the bond pad. In thermally aged gold ball bonds, the gold above the intermetallic layer fractures. The energy required to fracture a gold or copper ball bond of 1ml wire size is around 370Jm2, while an aged gold ball bond consumes about 520Jm2. Void nucleation and coalescence mechanism of ductile fracture takes place in the ball and stitch bonds, however, silicon particles may be the preferential void nucleation sites in bond pad aluminum metallization failures. To understand the second bond strength, a stitch pull test was conducted and the results showed the neck of the stitched wire cracks thus leaving behind a tail bond on the lead finger.

Copyright © 2006 by American Society of Mechanical Engineers
Your Session has timed out. Please sign back in to continue.



Grahic Jump Location
Figure 1

SEM observations of ball bond interface after dissolving the aluminum using 20% NaOH solution for the conditions; 1ml Au (a) 97Hz frequency, (b) 113Hz frequency, (c) 138Hz frequency, and (d) 2ml Cu, 138Hz frequency

Grahic Jump Location
Figure 2

Load-time and load-tool tip displacement curves obtained for the conditions: gold ball bonds of 1ml wire size; (a) and (b) 50 SR, 5 SH, (c) and (d) 300 SR, 5 SH, (e) and (f) 300 SR, 5 SH, 3h thermal aged, and (g) and (h) 300 SR, 5 SH, 7h thermal aged

Grahic Jump Location
Figure 3

Load-time and load-tool tip displacement curves obtained for copper ball bonds tested at 300 SR and 5 SH for the wire diameters; (a) and (b) 1, (c) and (d) 2, and (e) and (f) 4ml

Grahic Jump Location
Figure 4

Sectional micrographs showing structures of 1ml wire ball bonds (a) gold nondestructive tested at 20gm (b) higher magnification of (a), optical observations; (c) gold bond, and (d) copper bond

Grahic Jump Location
Figure 5

EDAX and macrostructures of sheared interfaces gold 1ml wire ball bond without aging; (a) SEM observation of ball bond interface, (b) EDAX on the interface area, (c) optical image of bond pad after shear, and (d) EDAX on the bond pad residual surface

Grahic Jump Location
Figure 6

Sheared copper ball bond interfaces observed in SEM by SE mode; (a) 1, (b) 2, (c) 4, (d) 4ml, observed by backscattered mode (e) 4ml, x-ray dot mapping of aluminum, and (f) optical imaging

Grahic Jump Location
Figure 7

SEM observations and EDAX on bond pad surface of 2ml copper ball bonded unit after shear; (a) SEM micrograph and (b) EDAX

Grahic Jump Location
Figure 8

Percentage of area fraction of the sticking aluminum on the copper ball bond interface after shearing

Grahic Jump Location
Figure 9

Observation of sheared wire bond interface for the conditions: Au 1ml wire bonds on thermal aging at 175°C for 7h; (a) SEM observation of ball bond sheared interface, (b) optical observation of bond pad after shear, (c) EDAX on the sheared ball and retained gold on the bond pad, (d) and (e) copper wire fractured at the end of the tail leaving behind the well bonded portion on the finger

Grahic Jump Location
Figure 10

Schematic illustration of the crack propagation in (a) gold ball bonds without aging, (b) copper ball bonds, and (c) thermal aged gold ball bonds




Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In