Influence of surface contamination on metal/metal bond contact quality |
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Authors: | A Schneuwly P Gröning L Schlapbach V P Jaecklin |
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Affiliation: | (1) Institute of Physics, Pérolles, CH-1700 Freiburg, Switzerland;(2) ESEC SA, Hinterbergstrasse 32, CH-6330 Cham, Switzerland |
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Abstract: | The influence of surface cleanliness of Au/Ni coated multichip materials (MCMs), Ag plated Cu lead frames, and Al bond pads
on semiconductor chips on the strength of Au wire bond contacts has been investigated. A clean surface is important for good
adhesion in any kind of attachment process. Investigations by means of x-ray photoelectron spectroscopy have been performed
on the bond substrates to determine the chemical composition, the nature as well as the thickness of the contamination layer.
The influence of contamination on bond contact quality has been examined by pull force measurements, which is an established
test method in semiconductor packaging industry for evaluating the quality of wire bonds. The results clearly show that a
strong correlation between the degree of contamination of the substrate and pull strength values exists. Furthermore, a contamination
thickness limiting value of 4 nm for Au and Ag substrates was determined, indicating good wire bond contact quality. The effect
of plasma cleaning on wire bondability of metallic and organic (MCMs) substrates has been examined by pull force measurements.
These results confirm the correlation between surface contamination and the strength of wire bond contacts for Au/Ni coated
MCMs and Ag plated Cu lead frames. Atomic force microscopy measurements have been performed to determine the roughness of
bond surfaces, demonstrating the importance of nanoscale characterization with regard to the bonding behavior of the substrates.
Finally, bonding substrates used in integrated circuit packaging are discussed with regard to their Au wire bonding behavior.
The Au wire bonding process first results in a cleaning effect of the substrate to be joined and secondly enables the change
of bonding energy into frictional heat giving rise to an enhanced interdiffusion at the interface. |
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Keywords: | Ag plated Cu lead frames Al bond pads Au/Ni coated multichip material (MCM) Au wire bonding surface contamination plasma cleaning x-ray photoelectron spectroscopy (XPS) |
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