Introduction:Introduction:

Metallization of non-conductive surfaces is important in many industrial applications as it lowers cost, Metallization of non-conductive surfaces is important in many industrial applications as it lowers cost, allows more flexibility in parts design, and reduces weight compared to its metal counterpart. Plating allows more flexibility in parts design, and reduces weight compared to its metal counterpart. Plating on plastics (POP) therefore has been developed and widely involved in manufacturing printed circuit on plastics (POP) therefore has been developed and widely involved in manufacturing printed circuit boards (PCB) and automobile parts, and in the electromagnetic interference (EMI) shielding boards (PCB) and automobile parts, and in the electromagnetic interference (EMI) shielding application. Having excellent electrical conductivity and being relatively inexpensive, copper (Cu) has application. Having excellent electrical conductivity and being relatively inexpensive, copper (Cu) has been widely studied for POP and a variety of plastics have been Cu plated including acrylonitrile-been widely studied for POP and a variety of plastics have been Cu plated including acrylonitrile-butadiene-styrene (ABS), polypropylene, and Teflon. butadiene-styrene (ABS), polypropylene, and Teflon.

Bath #Bath #

Electroless Cu Deposition Electroless Cu Deposition Bath Composition (wt %)Bath Composition (wt %)

CuSOCuSO44 HFHF

11 55 00

22 1010 00

33 55 1010

44 1010 6.76.7

55 1010 1010

66 55 1515

Paste Paste ##

Paste Composition (wt %)Paste Composition (wt %)Tape Test Tape Test

ResultResultAlAl CC EnamelEnamel HH22OO

11 2525 22 3030 4343 FailFail

22 2525 33 4242 3030 PassPass

33 2525 33 4444 2828 FailFail

44 3030 33 4040 2727 PassPass

55 3030 55 4040 2525 FailFail

66 3030 55 4040 2525 PassPass

77 3030 66 5050 1414 PassPass

88 3232 66 4848 1414 FailFail

99 3232 88 4545 1515 FailFail

1010 3535 44 4040 2121 FailFail

1111 4040 33 3636 2121 PassPass

1212 4040 88 4242 1010 FailFail

A process has been developed at the ATMC to convert non-conductive plastic surfaces into conductive A process has been developed at the ATMC to convert non-conductive plastic surfaces into conductive by coating either aluminum or aluminum-carbon black containing enamel pastes onto Acrylonitrile by coating either aluminum or aluminum-carbon black containing enamel pastes onto Acrylonitrile Butadiene Styrene (ABS) plastics to create Aluminum-seeded surfaces for a subsequent copper Butadiene Styrene (ABS) plastics to create Aluminum-seeded surfaces for a subsequent copper deposition. Through a simple electrolessdeposition. Through a simple electrolessprocedure, copper is able to reduce on the Al seeds and propagate on the procedure, copper is able to reduce on the Al seeds and propagate on the ABS surface to develop into ABS surface to develop into a conductive layer in about 10 min deposition time. Standard tape test, electrical conductivity a conductive layer in about 10 min deposition time. Standard tape test, electrical conductivity measurement, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) measurement, scanning electron microscope (SEM), and energy dispersive X-ray spectroscopy (EDS) were used to characterize the coated ABS surface before and after electroless Cu deposition. The were used to characterize the coated ABS surface before and after electroless Cu deposition. The study shows that the addition of carbon black study shows that the addition of carbon black particles to the pastes shorten the time to reach the particles to the pastes shorten the time to reach the maximum conductivity and enhance the adhesion of electrolessly deposited copper layer to the ABS maximum conductivity and enhance the adhesion of electrolessly deposited copper layer to the ABS substrate surface. The electroless copper deposition process developed in this study may open up a substrate surface. The electroless copper deposition process developed in this study may open up a new route of plating on plastics for printed circuit boards, electromagnetic interference shielding, and new route of plating on plastics for printed circuit boards, electromagnetic interference shielding, and many other applications. many other applications. Surface Preparation:Surface Preparation:

Al powder, C powder, enamel, and distilled water Al powder, C powder, enamel, and distilled water were mixed at different weight ratios and were mixed at different weight ratios and magnetically stirred vigorously for 1 hour to form magnetically stirred vigorously for 1 hour to form pastes which were called Al-C pastes. The Al-C pastes pastes which were called Al-C pastes. The Al-C pastes were then applied on ABS boards that were pre-cut were then applied on ABS boards that were pre-cut into ~5 × 5 cminto ~5 × 5 cm22 squares, and pre-cleaned with soap squares, and pre-cleaned with soap and distilled water. The Al-C paste coated ABS was and distilled water. The Al-C paste coated ABS was allowed to dry overnight at room temperature to be allowed to dry overnight at room temperature to be ready for the subsequent experiments. For ready for the subsequent experiments. For comparison, pastes without C particles were also comparison, pastes without C particles were also prepared by mixing Al powder, enamel, and distilled prepared by mixing Al powder, enamel, and distilled water and by following the same preparation water and by following the same preparation procedure as that of the Al-C pastes. These pastes procedure as that of the Al-C pastes. These pastes were called Al pastes. The Al pastes were applied on were called Al pastes. The Al pastes were applied on ABS boards in the same way as were the Al-C pastes ABS boards in the same way as were the Al-C pastes to prepare the Al paste coated ABS surface. to prepare the Al paste coated ABS surface.

Adhesion Evaluation:Adhesion Evaluation:

The adhesion of Al and Al-C coatings to the ABS surface and that of The adhesion of Al and Al-C coatings to the ABS surface and that of the electrolessly deposited Cu layer to the coated surfaces were the electrolessly deposited Cu layer to the coated surfaces were evaluated using the standard ASTM Scotch-tape test (ASTM D 3359) evaluated using the standard ASTM Scotch-tape test (ASTM D 3359) with minor modifications – a 25 kg weight was placed onto the test with minor modifications – a 25 kg weight was placed onto the test surface and remained for 5 minutes before the tape was pulled off, surface and remained for 5 minutes before the tape was pulled off, as shown in Fig. 1. The resulting surface was examined to evaluate as shown in Fig. 1. The resulting surface was examined to evaluate the adhesion performance. the adhesion performance. Bath Formulation:Bath Formulation:

Al or Al-C paste coated ABS squares were scoured with 300-grit Al or Al-C paste coated ABS squares were scoured with 300-grit sandpaper, rinsed with tap water, and dried in an oven pre-heated sandpaper, rinsed with tap water, and dried in an oven pre-heated to 40 ºC for 30 minutes. The scoured ABS squares were then to 40 ºC for 30 minutes. The scoured ABS squares were then immersed into the electroless Cu deposition bath containing CuSOimmersed into the electroless Cu deposition bath containing CuSO44 and HF at different concentrations for different time (from 1 to 60 and HF at different concentrations for different time (from 1 to 60 min). In this study, the CuSOmin). In this study, the CuSO44 concentrations varied from 5 ~ 15 wt concentrations varied from 5 ~ 15 wt%, and those of HF were 5 wt% and 10 wt%. Two types of %, and those of HF were 5 wt% and 10 wt%. Two types of electroless deposition bath were studied with or without HF and the electroless deposition bath were studied with or without HF and the detailed information of these deposition baths was shown in Table detailed information of these deposition baths was shown in Table 2. The Cu deposited ABS squares were then dried in the oven pre-2. The Cu deposited ABS squares were then dried in the oven pre-heated to 40 ºC for 30 minutes and ready for electrical conductivity heated to 40 ºC for 30 minutes and ready for electrical conductivity measurement. measurement.

Table 1Table 1

Table 2Table 2

Fig. 1Fig. 1

Electroless Copper Deposition onElectroless Copper Deposition onAluminum-seeded ABS PlasticsAluminum-seeded ABS Plastics

Dapeng LiDapeng LiDepartment of Materials and TextilesDepartment of Materials and TextilesUniversity of Massachusetts – DartmouthUniversity of Massachusetts – Dartmouth

Kate GoodwinKate GoodwinDepartment of Chemistry and BiochemistryDepartment of Chemistry and BiochemistryUniversity of Massachusetts – DartmouthUniversity of Massachusetts – Dartmouth

Chen-Lu YangChen-Lu YangAdvanced Technology and Manufacturing CenterAdvanced Technology and Manufacturing CenterUniversity of Massachusetts – DartmouthUniversity of Massachusetts – Dartmouth

DepositioDeposition n

(min)(min)

Resistance (Ohm/cmResistance (Ohm/cm22 x 10 x 1033))

Al paste coated ABSAl paste coated ABS Al-C paste coated ABSAl-C paste coated ABS

11 >> >>

22 >> 846.9 ± 714.4846.9 ± 714.4

55 25.1 ± 31.525.1 ± 31.5 1.7 ± 1.51.7 ± 1.5

1010 26.4 ± 20.426.4 ± 20.4 1.0 ± 0.21.0 ± 0.2

2020 1.3 ± 0.61.3 ± 0.6 0.8 ± 0.40.8 ± 0.4

3030 0.8 ± 0.40.8 ± 0.4 0.8 ± 0.30.8 ± 0.3

4040 1.0 ± 0.61.0 ± 0.6 0.40.4

5050 0.6 ± 0.30.6 ± 0.3 0.6 ± 0.20.6 ± 0.2

6060 0.5 ± 0.10.5 ± 0.1 0.7 ± 0.10.7 ± 0.1

Electrical Performance:Electrical Performance:

Shown in Table 3 are the electrical resistance Shown in Table 3 are the electrical resistance measurement of both Al and Al-C paste coated ABS measurement of both Al and Al-C paste coated ABS after electroless Cu deposition for different time. At after electroless Cu deposition for different time. At 1 min deposition time, both Al and Al-C paste 1 min deposition time, both Al and Al-C paste coated ABS samples show immeasurable coated ABS samples show immeasurable resistance, indicating their poor conductivity. After resistance, indicating their poor conductivity. After 2 min deposition, the Al-C paste coated ABS 2 min deposition, the Al-C paste coated ABS becomes conductive with a measured resistance of becomes conductive with a measured resistance of 846.9 ± 714.4 Ohm/cm846.9 ± 714.4 Ohm/cm22, while the Al paste coated , while the Al paste coated sample still yields immeasurable resistance, and it sample still yields immeasurable resistance, and it is not conductive until deposited for 5 min (25.1 ± is not conductive until deposited for 5 min (25.1 ± 31.5 Ohm/cm31.5 Ohm/cm22). ).

Metal Identification:Metal Identification:

As illustrated in Fig. 3, the EDS spectrum As illustrated in Fig. 3, the EDS spectrum of the scoured ABS surface is dominated of the scoured ABS surface is dominated by Al at 1.487 keV (Kα, red arrow in the by Al at 1.487 keV (Kα, red arrow in the Fig.). With the increase of deposition Fig.). With the increase of deposition time, the Al peak decreases and is time, the Al peak decreases and is replaced by three Cu peaks at 0.930 keV replaced by three Cu peaks at 0.930 keV (Lα), 8.041 keV (Kα), and 8.905 keV (Kβ), (Lα), 8.041 keV (Kα), and 8.905 keV (Kβ), and at the 60 min deposition time, the and at the 60 min deposition time, the entire surface appears to be dominated entire surface appears to be dominated by Cu. These are evident that Cuby Cu. These are evident that Cu2+2+ has has been reduced by the Al particles seeded been reduced by the Al particles seeded on ABS and gradually propagated to cover on ABS and gradually propagated to cover the surface over time until a maximum the surface over time until a maximum coverage level is reached to lead to the coverage level is reached to lead to the minimum resistance. minimum resistance.

Copper Deposition:Copper Deposition:

Scanning electron microscope Scanning electron microscope was used to investigate the was used to investigate the deposition of copper on Al-C paste deposition of copper on Al-C paste coated ABS samples. Fig. 2 shows coated ABS samples. Fig. 2 shows the SEM images of Al-C paste the SEM images of Al-C paste coated ABS before (a) and after coated ABS before (a) and after scouring (b), and of the scoured scouring (b), and of the scoured ABS after electroless Cu ABS after electroless Cu deposition for different time. (c) 1 deposition for different time. (c) 1 min, (d) 2 min, (e) 5 min, (f) 60 min, (d) 2 min, (e) 5 min, (f) 60 min. min.

Fig. 2Fig. 2

(a)

(d)

(b)

(e)

(c)

(f)

Table 3Table 3

0

100

200

300

400

500

0 2 4 6 8 10keV

X-r

ay c

ount

s

After scouring

1 min

5 min

60 min

Fig. 3Fig. 3

0

20

40

60

80

100

0 10 20 30 40 50 60 70

Time (min)

Wt

%

Cu Al

C O

b

Fig. 4 Shows the composition change of the Fig. 4 Shows the composition change of the Al-C paste coated ABS surface as a function Al-C paste coated ABS surface as a function of deposition time. Three randomly of deposition time. Three randomly selected areas of each ABS sample were selected areas of each ABS sample were EDS analyzed to obtain the compositions. EDS analyzed to obtain the compositions.

Fig. 4Fig. 4

d4d1 d2 d3

c1 c2 c3 c4a1 a2 a3

b1 b2 b3

EDS Microanalysis:EDS Microanalysis:

Fig. 5 shows the EDS maps of the Al paste coated ABS surface before (a1-a3) and after scouring (b1-b3), Fig. 5 shows the EDS maps of the Al paste coated ABS surface before (a1-a3) and after scouring (b1-b3), and the scoured ABS surface after 1 min (c1-c4) and 60 min (d1-d4) of electroless Cu deposition (Bar and the scoured ABS surface after 1 min (c1-c4) and 60 min (d1-d4) of electroless Cu deposition (Bar length = 60 µm). Green: Al, Red: C and, Blue: Cu (Same for all other EDS maps).length = 60 µm). Green: Al, Red: C and, Blue: Cu (Same for all other EDS maps).

Fig. 5Fig. 5

a1 a2 a3 a4

The deposition of Cu on Al-seeded ABS surface The deposition of Cu on Al-seeded ABS surface has changed the elemental distribution. Fig. 5 has changed the elemental distribution. Fig. 5 c1-c4 show the propagation of Cu on ABS c1-c4 show the propagation of Cu on ABS surface over deposition time. One can see surface over deposition time. One can see clearly from Fig. 5 c1-c4 that Cu particles start clearly from Fig. 5 c1-c4 that Cu particles start growing on the surface of several Al seeds, but growing on the surface of several Al seeds, but only part of the area of those seeds is covered only part of the area of those seeds is covered by Cu at that deposition time. After 60 min, by Cu at that deposition time. After 60 min, however, a continuous Cu layer has developed however, a continuous Cu layer has developed to almost fully cover the surface, leaving only to almost fully cover the surface, leaving only a few scattered spots remained “naked” (Fig. a few scattered spots remained “naked” (Fig. 5 d4). 5 d4).

Cross section of the Al-C paste coated ABS was also EDS mapped (Fig. 6 a2-a4). A Cu layer of about Cross section of the Al-C paste coated ABS was also EDS mapped (Fig. 6 a2-a4). A Cu layer of about 10~15 µm thick has been formed on the top surface (Fig. 6 a4) and such a thickness appears to agree 10~15 µm thick has been formed on the top surface (Fig. 6 a4) and such a thickness appears to agree with the height of Cu particles, namely, a single layer of Cu particles is deposited on the ABS surface. with the height of Cu particles, namely, a single layer of Cu particles is deposited on the ABS surface.

Fig. 6Fig. 6

Conclusions:Conclusions: Al or Al-C containing enamel pastes were coated onto ABS plastic to create Al-seeded surfaces onto which Al or Al-C containing enamel pastes were coated onto ABS plastic to create Al-seeded surfaces onto which Cu could be readily deposited through a simple electroless procedure, converting the non-conductive Cu could be readily deposited through a simple electroless procedure, converting the non-conductive plastic surface into conductive. Standard tape test, electrical conductivity measurement, SEM, and EDS plastic surface into conductive. Standard tape test, electrical conductivity measurement, SEM, and EDS were used to characterize the coated ABS surface before and after electroless Cu deposition. It was found were used to characterize the coated ABS surface before and after electroless Cu deposition. It was found that addition of C particles to the pastes shortened the time to reach the maximum conductivity and that addition of C particles to the pastes shortened the time to reach the maximum conductivity and enhanced the adhesion of electrolessly deposited Cu layer to the substrate. The electroless Cu deposition enhanced the adhesion of electrolessly deposited Cu layer to the substrate. The electroless Cu deposition process developed in this study may open up a new route of deposition on plastics (POP) for printed circuit process developed in this study may open up a new route of deposition on plastics (POP) for printed circuit boards, electromagnetic interference shielding, and many other applications. We realized that the boards, electromagnetic interference shielding, and many other applications. We realized that the following studies are important to optimize the paste formula and to elucidate the mechanism of Cu following studies are important to optimize the paste formula and to elucidate the mechanism of Cu growth on the Al seeds:growth on the Al seeds:• The role HF plays in enhancing the Cu deposition; The role HF plays in enhancing the Cu deposition;

• The role C plays in improving the conductivity at short deposition times and enhancing the adhesion of The role C plays in improving the conductivity at short deposition times and enhancing the adhesion of the deposited Cu layer to the substrate.the deposited Cu layer to the substrate.

University of Massachusetts Dartmouth Chapter of Sigma Xi, the Scientific Research SocietyUniversity of Massachusetts Dartmouth Chapter of Sigma Xi, the Scientific Research Society1515thth Annual UMass Dartmouth Research Exhibition Annual UMass Dartmouth Research ExhibitionApril 28-29, 2009April 28-29, 2009