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Figure 7: Normalized ductility of a) medium; and b) high-purity copper as a function of the deposit thickness for copper only (•), as well as a composite of copper
and dielectric (•).
conducting, the roughness of the of the ductility of the composite in materials of the package may no longer
polymer-facing side of the adhesion comparison to the individual copper be considered as individual, but as a
promoter does not lead to elongation materials. The reinforcement was whole. This approach allows significant
of the high-frequency signal path on much more pronounced for high-purity reinforcement of the mechanical
account of the skin effect. Other than copper deposits. While the benefit in properties upon a combination of high-
with a roughening adhesion promoter, case of medium-purity copper started purity copper material with a suitable
with A P2 the conductive copper smaller at low deposit thickness and adhesion promoter.
surface retains the flatness of the as- diminished upon increasing thickness,
deposited surface, ensuring the same t h e d u c t i l i t y b e c a m e v i r t u a l l y References
suitability for 5G, radar, and other independent of the thickness in the 1. C. Melvin, R. Massey, Chip Scale
high-frequency applications. case of high-purity copper. Review 2017, 21, 40-44.
T h e e f f e c t s o f t h e c o p p e r 2. R. Schmidt, T. Beck, R. Rooney,
deposit thickness on ductility, the Summary A. A. Gewirth, “Optimization of
corresponding scaling issue, and the Chemistry solutions can help to electrodeposited copper for sub-
approach to overcome this issue upon optimize the reliability of copper 5µm L/S redistribution layer lines
composite formation are summarized RDL traces, especially at decreasing by plating additives,” IEEE 68th
in Figure 7. A comparison of copper L/S dimensions. Optimization of the Electronic Components and Tech.
deposits without dielectric once more individual copper material may be Conf. (ECTC), 1220-1225 (2018).
shows lower ductility values of medium achieved by increasing the purity
purity (Figure 7a) in comparison to of the deposit via proper design of
high purity (Figure 7b). The decrease organic additives. Further significant
of ductility upon decreasing deposit reinforcement of the mechanical
thickness was referred to earlier as properties may be obtained by using a
a scaling issue. In general, a strong holistic approach, i.e., using synergies
stabilization of fine copper structures with the surrounding materials within
by proper composite formation with the package. Proper adhesion between
the dielectric was observed. This could copper and dielectric allows composite
be deduced from the strong increase formation. Therefore, the various

Biographies
Ralf Schmidt is Manager R&D Semiconductor at Atotech Group, Berlin, Germany. He holds a PhD in
Organic Chemistry and joined the company in 2011. Before his current position, he was team manager in the
central R&D department at Atotech. Email ralf.schmidt@atotech.com
Thomas Beck is Regional VP, South East Asia at Atotech Group, Berlin, Germany. Prior to his current
position, he was Global Product Director Semiconductor—responsible for the definition of R&D projects,
integration/introduction and marketing-related activities for ECD (pillar/RDL) and electroless (ENEPIG)
processes, respectively, and lead frame and connector products.

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