Electroless plating of solid metals from a solution onto a catalytically active surface has been widely used in the printed circuit board industry for production of wiring layers and inter-layer (via) connections. More recently, this body of knowledge has been applied to producing metal interconnect films in the integrated circuit substrate (IC substrate) industry. Proper surface activation (through a catalyst) is the key to electroless plating, however there are difficulties in controlling the uniformity of the catalyst coverage. For smooth substrate surfaces, like polyimide (PI) which is used in flexible electronics applications, there is an additional challenge for the electrolessly plated metal to adhere to the surface. Although traditional methods such as plasma and desmearing processes have been used to “roughen” the surface for greater adhesion through an interlock mechanism, electroless metal deposited on a rough substrate would result in signal loss in high speed high frequency applications, such as 5G communication electronics. It is therefore desirable to develop new chemistries that can be used for planarization of the substrate to generate a smooth metal-substrate interface, but with an enhanced adhesion strength of the deposited metal, therefore eliminating the need for an interlocking rough interface. The mussel-inspired adhesive moiety, dopamine, is known to be a universal adhesive on a wide range of inorganic and organic surfaces.1 The mechanism of such strong adhesion is still under investigation; however, catechols and amines are known to induce strong interactions with substrates and self-polymerization.1 Our recent work on dopamine-functionalized polymers demonstrated that the dopamine end group stabilized ultrathin (5-10 nm) polymer films and formed conformal coatings on planar and non-planar surfaces.2 Moreover, another mussel-inspired adhesive moiety, histamine, is known to form an ionic bond with metals, which can be useful in the coordination of the ionic catalyst. Therefore, by utilizing a random copolymer of histamine and dopamine moieties with a water-soluble poly (ethylene oxide) backbone (PEO-PHis-PDopa), we can facilitate adhesion between smooth substrates and also enable the planarization of copper in electroless copper plating. When the copolymer is deposited on a substrate surface, the Dopa moiety reacts with the substrate and adheres to it, the polymer chain extends and folds to generate a smoother outer surface through minimizing the surface energy, while the histamine moiety coordinates with the ionic catalyst (Pd). Fig.1 shows a schematic where the PEO-PHis-PDopa layer plays two roles: an adhesion promoter and a surface smoother at the same time.

1. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
MUSSEL INSPIRED POLYMERS FOR
FLEXIBLE ELECTRONICS APPLICATIONS
Hellen Papananou,1 Reika Katsumata,1 Rubayn Goh1,
Feng Liu2, Mingqi Li2, Peter Trefonas2, Rachel Segalman1,3
1 Materials Research Laboratory, University of California, Santa Barbara, California, U.S.A
2 DuPont Specialty Products Division–Electronics & Imaging, Marlborough, Massachusetts, U.S.A.
3 Department of Chemical Engineering, University of California, Santa Barbara, California, U.S.A

2. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Vias, holes, connections and contacts: Cu
2
Deposition achieved through an auto
catalytic reaction via a reducing agent
Electrolysis which uses direct electric
current to dissolve a copper rod and
transport the copper ions to the substrate
Conventional Circuit Board

3. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
No adhesion between Cu and substrate
Substrate: Polyimide (PI)
Copper
Substrate
Electroless Copper
Substrate
Adhesive
Non-conductive Electroless plating
Electroless Copper
Substrate
Adhesive
Electrolytic Copper
3

4. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Additional requirements from application perspective
1. Cost effective
2. Process should be no longer than several min
3. Moderate temperatures: from R.T. to 50 °C
4. Water-based system
4

5. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Adhesive moieties: inspiration
5
Dopamine
Histamine
Catechol
Imidazole
Single-molecule mechanics of mussel adhesion
Haeshin Lee, Norbert F. Scherer, and Phillip B. Messersmith
PNAS, 2006 103 (35) 12999-13003

6. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
6
POLYMER
PEO-stat-AGE
Poly(ethylene oxide)-allyl glycidyl ether
Mw=20.000
AGE%~5%
PEO-HISTA
Water soluble
Tailorability
Thiol-ene
reaction
+

7. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
7
POLYMER
PEO-stat-AGE
Poly(ethylene oxide)-allyl glycidyl ether
Thiol-ene
reaction
Mw=20.000
AGE%~5%
PEO-DOPA
Water soluble
Tailorability

8. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Copper plating process
Rinse
1 min
Microetch
H2SO4/
Na2SO4 aq.
R.T.
1.5 min
Pre-dip
HNO3 aq.
R.T.
0.5 min
Rinse
2 min
Rinse
1 min
Reducer
DMAB/
B(OH)3 aq.
32 °C
1 min
Pre-
treatment of
substrates
This studyConventional process “Control”
Cationic polymer
PIPI
– +
+
+ +
++
–
– –
Polymer
PI PI
OHOH NH
8
UVO
treatment
R.T.
5 min
PI PI
OHOH OH
Ionic
catalyst
CP 6530
40 °C
1 min
Polymer
PI
Pd Pd2+
Pd2+
Polymer
PI
Copper
Pd
Rinse
2 min
N2 dryRinse
1 min
Plating
CP 6550
43 °C
6 min

9. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Goal
1. Achieve smooth surface of copper
2. Enhance adhesion between PI and copper and
understand the mechanism of adhesion promotion and
planarization
9

10. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Cu Plating with PEO-Hista
10
PH=3 PH=5.5 PH=6.5 PH=8

11. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Cu Plating with PEO-Dopa
11
PH=3 PH=5.5 PH=8 PH=9

12. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Smooth surface
DOW CONTROL PEO-HISTA PEO-DOPA
RMS=16nm RMS=9nm RMS=7.5nm
12

13. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Goal
1. Achieve smooth surface of copper
2. Enhance adhesion between PI and copper and
understand the mechanism of adhesion promotion and
planarization
Goal
 Achieve smooth surface of copper
2. Enhance adhesion between PI and copper and
Understand the mechanism of adhesion promotion and
planarization
13

14. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Scotch tape test
14
Adhesion on Passed/times Failed/times
CONTROL  10 0
PEO-HISTA  5 0
PEO-DOPA  4 1

15. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Step-by-step study of roughness (AFM)
15
0
2
4
6
8
10
12
14
16
18
20
As received Plasma Polymer Microetch Catalyst Cu
RMSroughness2µm×2µm
(nm)
Control PEO-HISTA PEO-DOPA
PIPI
PEO-PDOPA
PI
PEO-PDOPA
PI
Pd
PEO-PDOPA
PI
Copper
Pd
PEO-PDOPA
PI

16. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
16
XPS STUDY
N1s
Cu2p
Focusofthepeak
Pd3d
C1s
O1s
PEO-PDOPAPEO-PDOPA
Plasma
Treatment
Polymer Micro etch Pre-dip Ionic catalyst Reducer Plating
PI PI PI PI
PEO-PDOPA
PI
Pd
PEO-PDOPA
PI
Copper
Pd
PEO-PDOPA
PI
Pd
PEO-PDOPA
PI
Kapton
As received

17. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
17
Dupont recipe
P(EO-His)
pH = 3
Pretreatment
C1s
O
O
O
m n
S
HN
O
NH
N
P(EO-Dopa)
pH = 3
?
285.0 C-C, C-H
286.5 C-O-C, C-OH
288.0 C=O

18. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
18
Dupont recipe
P(EO-His)
pH = 3
Pretreatment
N1s
O
O
O
m n
S
HN
O
NH
N
P(EO-Dopa)
pH = 3
?
399.0 N-H
400.7 ?

19. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
19
Dupont recipe
P(EO-His)
pH = 3
Pd3d
O
O
O
m n
S
HN
O
NH
N
P(EO-Dopa)
pH = 3
?

20. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
20
Dupont recipe
P(EO-His)
pH = 3
Cu2p
O
O
O
m n
S
HN
O
NH
N
P(EO-Dopa)
pH = 3
?

21. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Which interface is failing?
21
PEO-HISTA
PI PI
OHOH NH
PEO-HISTA
PI
Pd Pd2+
Pd2+
PEO-DOPA
PI PI
OHOH NH
PEO-DOPA
PI
Pd Pd2+
Pd2+
?

22. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Future:
PEO-stat-HISTA-stat-DOPA
22
Good adhesion to
the substrate
Better quality of
plated copper
Mw of PEO % AGE

23. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
Conclusions
23
Both polymers
successfully acted
as an adhesive
during electroless
plating
We were able to
synthesize water
soluble polymers
with mussel inspired
moieties
One of our polymers
exhibits the same
adhesion strength
as control
Both polymers had
better quality of
plated copper than
control

24. Eleni Papananou EPF CONFERENCE 19_06_11Segalman Group
24
Acknowledgements
• Patent application has been filed.
• Team
• Dr. Feng Liu (DuPont)
• Dr. Mingqi Li (DuPont)
• Dr. Peter Trefonas (DuPont)
• Prof. Reika Katsumata
• Prof. Rachel A. Segalman
• Special thanks to…
• Dr. Segolene Antoine
• Rubayn Goh
• Nicole Michenfelder-Schauser