Coatings

Abstract

The present invention provides an electronic or electrical device or component thereof comprising a cross-linked polymeric coating on a surface of the electronic or electrical device or component thereof; wherein the cross-linked polymeric coating is obtainable by exposing the electronic or electrical device or component thereof to a plasma comprising a monomer compound and a crosslinking reagent for a period of time sufficient to allow formation of the cross-linked polymeric coating on a surface thereof, wherein the monomer compound has the following formula: ##STR00001##
where R.sub.1, R.sub.2 and R.sub.4 are each independently selected from hydrogen, optionally substituted branched or straight chain C.sub.1-C.sub.6 alkyl or halo alkyl or aryl optionally substituted by halo, and R.sub.3 is selected from: ##STR00002##
where each X is independently selected from hydrogen, a halogen, optionally substituted branched or straight chain C.sub.1-C.sub.6 alkyl, halo alkyl or aryl optionally substituted by halo; and n.sub.1 is an integer from 1 to 27; and wherein the crosslinking reagent comprises two or more unsaturated bonds attached by means of one or more linker moieties and has a boiling point at standard pressure of less than 500° C.

Claims

1. An electronic or electrical device or electronic or electrical component thereof comprising a protective cross-linked polymeric coating on a surface of the device or component; wherein the protective cross-linked polymeric coating is obtained by exposing the device or component to a plasma comprising a monomer compound and a crosslinking reagent for a period of time sufficient to allow formation of the protective cross-linked polymeric coating on a surface thereof, wherein the monomer compound has the following formula: ##STR00039## where R.sub.1, R.sub.2 and R.sub.4 are each independently selected from hydrogen, optionally substituted branched or straight chain C.sub.1-C.sub.6 alkyl or halo alkyl or aryl optionally substituted by halo, and R.sub.3 is selected from: ##STR00040## where each X is independently selected from hydrogen, a halogen, optionally substituted branched or straight chain C.sub.1-C.sub.6 alkyl, halo alkyl or aryl optionally substituted by halo; where A is aryl optionally substituted by halo; and n.sub.1 is an integer from 0 to 27; and wherein the crosslinking reagent comprises two or more unsaturated bonds attached by means of one or more linker moieties and has a boiling point of less than 500° C. at standard pressure the crosslinking reagent having one of the following structures: ##STR00041## where Y.sub.1, Y.sub.2, Y.sub.3, Y.sub.4, Y.sub.5, Y.sub.6, Y.sub.7 and Y.sub.8 are each independently selected from hydrogen, optionally substituted cyclic, branched or straight chain C.sub.1-C.sub.6 alkyl or aryl; and L is a linker moiety; wherein for compound (i) L is of formula A having one of the following structures: ##STR00042## and Y.sub.10 is selected from optionally substituted cyclic, branched or straight chain C.sub.1-C.sub.8 alkylene and a siloxane group; or wherein for compound (i) L is of formula B having the following formula: ##STR00043## where each Y.sub.9 is independently selected from, a bond, —O—, —O—C(O)—, —C(O)—O—, —Y.sub.11—O—C(O)—, —C(O)—O—Y.sub.11—, —OY.sub.11—, and Y.sub.11O—, where Y.sub.11 is an optionally substituted cyclic, branched or straight chain C.sub.1-C.sub.8 alkylene; and wherein Y.sub.10 has the following formula: ##STR00044## and each Y.sub.15 is independently selected from optionally substituted branched or straight chain C.sub.1-C.sub.6 alkyl; or wherein Y.sub.10 has the following formula: ##STR00045## and Y.sub.16 to Y.sub.19 are each independently selected from H and optionally substituted branched or straight chain C.sub.1-C.sub.8 alkyl or alkenyl or wherein Y.sub.10 has the following formula: ##STR00046## and each Y.sub.12 is fluoro and each Y.sub.13 is fluoro, and n is an integer from 1 to 10.

2. A device or component according to claim 1, wherein the protective cross-linked polymeric coating is a physical barrier to mass and electron transport.

3. A device or component according to claim 1, wherein the protective cross-linked polymeric coating forms a liquid repellent surface defined by a static water contact angle (WCA) of at least 90°.

4. A device or component according to claim 1, wherein n is from 4 to 6.

5. A device or component according to claim 1, wherein Y.sub.10 has the following formula: ##STR00047## and each Y.sub.15 is methyl, and each Y.sub.9 is a bond.

6. A device or component according to claim 1, wherein Y.sub.10 has the following formula: ##STR00048## and wherein Y.sub.18 is H or vinylene, and Y.sub.16, Y.sub.17 and Y.sub.19 are each H.

7. A device or component according to claim 1 wherein the crosslinking reagent is selected from 1,4-butanediol divinyl ether (BDVE), 1,4-cyclohexanedimethanol divinyl ether (CDDE), 1,2,4-trivinylcyclohexane (TVCH), 1,3-divinyltetramethyldisiloxane (DVTMDS), diallyl 1,4-cyclohexanedicarboxylate (DCHD), 1,6-divinylperfluorohexane (DVPFH), 1H,1H,6H,6H-perfluorohexanediol diacrylate (PFHDA) and glyoxal bis (diallyl acetal) (GBDA).

8. A device or component according to claim 1, wherein for compound (ii), L is selected from a branched or straight chain C.sub.1-C.sub.8 alkylene or an ether group.

9. A device or component according to claim 1 wherein each X is H.

10. A device or component according to claim 1, wherein each X is F.

11. A device or component according to claim 1, wherein the device or component is selected from a mobile phone, smartphone, pager, radio, sound and audio system, hearing aid, personal audio equipment, television, DVD player including portable a DVD player, video recorder, digi or other set-top boxes, computer or related component, personal digital assistant (PDA), keyboard, instrument, games console, data storage device, outdoor lighting system, radio antennae or other form of communication equipment, or printed circuit board.

12. A device or component according to claim 11, wherein the sound and audio system is a loudspeaker, microphone, ringer and/or buzzer.

13. A device or component according to claim 11, wherein the personal audio equipment is a personal CD, tape cassette or MP3 player.

14. A device or component according to claim 11, wherein the computer or related component is a laptop, notebook, tablet, phablet or palmtop computer.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The present invention will now be further described with reference to the following non-limiting examples and the accompanying illustrative drawings, of which:

(2) FIG. 1 illustrates shows the effect of increasing the power to monomer flow ratio for CW plasmas in a 3 litre chamber in a prior art process.

(3) FIG. 2 shows the same effect for pulsed plasma conditions.

(4) FIG. 3 shows a tapping mode image over 10×10 μm.sup.2 field of view of a specimen example (thickness d=1230 nm) prepared according to Example 1 (left hand side) and a contour line plot showing the data used for calculation of RMS roughness (right hand side). The ΔZ value indicated on the plot has been taken over an area of the graph that represents the majority of the coating. Peaks that lie above the ΔZ range indicate large particles and troughs that fall below the ΔZ range show voids or pinholes in the coating. The width of the peaks also gives an indication of the particle size.

(5) FIG. 4 illustrates the effect of adding the divinyl adipate crosslinker to perfluorooctyl acrylate on water contact angle from a process on a 125 Litre chamber.

(6) FIG. 5 shows the effect of adding crosslinkers in accordance with the invention on the electrical resistance per nm of the coatings.

(7) FIG. 6 shows a tapping mode image of a 90 nm thick coating, prepared as described in Example 3, over 2×2 μm.sup.2 field of view (top left), a representative contour line indicating height variation (z-axis) of the coating (top right) and a phase image indicating full substrate coverage (bottom left); RMS roughness of the coating is 1.65 nm and Δz/d=0.05

(8) FIG. 7 shows a FTIR/ATR spectrum of a coating formed according to Example 5.

EXAMPLE 1

(9) Example of Plasma Polymerising PFAC6 with No Crosslinker in a 3 Litre Chamber

(10) PFAC6 was polymerised in a 3 litre glass chamber using a continuous plasma process. In the experimental matrix, the continuous plasma was produced using RF power levels of 50, 100 and 200 Watts. The process pressure was run at 30, 60 and 90 mTorr and the monomer flow rate run at 50, 100 and 200 microlitres of liquid per minute. The duration of the process was either 10 or 40 minutes. The coated substrate was silicon wafer and whether the coating was tacky or not was determined by wiping the substrate with a finger and determining by eye if the coating had smeared. The results in FIG. 1 indicate that for lower CW powers, the coating could easily be smeared (i.e. tacky), but by increasing the power to flow ratio, the coating became resistant to smearing (i.e. non-tacky) and this is expected to be due to additional crosslinking caused by more monomer fragmentation. The water contact angle was also seen to decline with increasing power to flow ratio, and this too is indicative of more power increasing the level of monomer fragmentation.

(11) The same 3 litre chamber was used to also look at the effect of power to flow ratios with pulsed plasma polymerisation. In these experiments, the peak power was either 250 or 500 W. The RF power feed was pulsed with an on time of 35 microseconds and off times of 5.5 and 1 millisecond. Process pressure was either 20, 35, 60 or 80 mTorr. The monomer flow was either 50 or 200 microlitres of liquid per minute. FIG. 2 shows that low power to flow conditions can generate coatings that can be smeared (tacky) and only by increasing the power could the smear be reduced. This too had a concomitant decline in water contact angle.

(12) The results from FIGS. 1 and 2 show that plasma processing PFAC6 on its own could only lead to smear-free coatings when the powers were high enough to decrease the other desirable property of the water contact angle This illustrates the need to add a crosslinker to prevent the coating smearing and maintain the water contact angle.

EXAMPLE 2

(13) Examples of Perfluoro Alkyl Acrylate Co-Polymerisation with Crosslinker to Show Improvements in Electrical Resistance

(14) Perfluorooctyl acrylate monomer was mixed with a single crosslinker from the following list:

(15) VINYL ESTERS: Divinyl adipate (DVA)

(16) VINYL ETHERS: 1,4-Butanediol divinyl ether (BDVE); 1,4 Cyclohexanedimethanol divinyl ether (CDDE)

(17) DI- or TM-VINYLS: 1,7-Octadiene (1,7-OD); 1,2,4-Trivinylcyclohexane (TVCH); DI VINYL with alkyl fluoro group: 1,6-divinylperfluorohexane (DVPFH)

(18) DI VINYL with silicon group: 1,3-Divinyl tetramethyldisiloxane (DVTMDS)

(19) DI VINYL with cyclic ring and carboxylate groups: Diallyl 1,4-cyclohexanedicarboxylate (DCHC)

(20) DI ACRYLATE: 1H1H,6H,6H-perfluorohexanediol diacrylate (PFHDA)

(21) The crosslinker was mixed with the PFAC6 as a percentage by volume for the following percentages: 20, 40, 60, 80, and 100%.

(22) Plasma initiated polymerisation reactions were carried out in a 3 litre glass plasma chamber. The substrates were test circuit boards. The PFAC6/crosslinker mixture was introduced at a rate of 0.04-0.06 ul/min and the process pressure was 40 mTorr. The process plasma consisted of a 1 minute continuous plasma (CW) step of 50 W followed by 10-20 minute pulsed plasma (PW) step of 50 W and RF power being delivered by a pulse sequence with a duty cycle of 6.9%. The coated circuit boards were immersed in tap water and an 8V potential was applied for 13 minutes. The final current readings, together with coating thickness measurements, were used to calculate the electrical resistance per nm of coating. FIG. 5 below shows the effect of adding a range of crosslinkers on the electrical resistance per nm of the barrier coatings. FIG. 5 clearly shows the improvement in resistance that can be gained by adding the crosslinker to the PFAC6 monomer. Furthermore, all of the crosslinkers tested gave non-smear/non-tacky coatings with concentration levels of 20% and above, with the exceptions of DVTMDS, DCHD, PFHDA and DVPFH which were non-smear at levels of 40% and above.

EXAMPLE 3

(23) Example of Crosslinker Concentration on Water Repellent Coating.

(24) Water repellent coatings were prepared in a 125 litre volume chamber using PFAC6 with different levels of divinyl adipate (DVA) and using helium as a carrier gas. The deposition process consisted of a 3 minute CW step with 300 W power and a pulsed step with 150 W power and an RF pulse duty cycle of 0.018%. Silicon wafer was used as the test substrates and the contact angle of the coated wafer was determined by applying a 3 ul drop of deionised wafer onto the coated wafer and measuring the contact angle using a VCA Optima (AST products) with image analysis software. The variation of contact angle with (v/v) % DVA crosslinker is shown in FIG. 4. It was also noted that for the 10 (v/v) % DVA concentration, the water drop left a mark on the coated wafer where it's circumference had been. This indicated that a higher level of crosslinker was required to give a more stable coating. This observation, in combination with the results in FIG. 4, suggest an optimum range of 20-40 (v/v) % DVA crosslinker, though this is likely to vary, typically within the range of from 10-60 (v/v) % for different monomers and crosslinkers and different chamber sizes.

(25) Pulsed plasma polymerisation of perfluoro alkyl acrylate in the presence of divinyl adipate (DVA) was carried out in a 125 litre chamber. FIG. 4 shows the effect of adding different liquid volume percentages of DVA crosslinker to perfluorooctyl acrylate on water contact angle on a silicon wafer substrate.

EXAMPLE 4

(26) Example of AFM Measurement of Monomer/Crosslinker Co-Polymer Coating

(27) A barrier-style coating was prepared in a 22 litre volume chamber using PFAC6 with 10% DVA. The deposition process consisted of a 1 minute CW step with a CW power to flow ratio of 3.9 (W/microliter/min), and a pulsed step with a PW power/monomer flow ratio of 0.28 (W/microlitres/min). FIG. 6 shows the representative topographical and phase contrast images were obtained from all the samples. High spatial resolution images show mainly the structures of areas between the raised features. The RMS roughness of the coating is 1.65 nm and the Δz/d=0.05. As the Δz/d value is <0.15, then this indicates that the physical layer is substantially pinhole free.

EXAMPLE 5

(28) Example of FTIR/ATR Measurement of Monomer/Crosslinker Co-Polymer Coating

(29) Two barrier-style coatings were prepared in a 22 litre volume chamber using PFAC6 only and PFAC6 with 10% DVA as described in example 4. The deposition process consisted of a 1 minute CW step with a CW power to flow ratio of 3.9 (W/microliter/min), and a pulsed step with a PW power/monomer flow ratio of 0.28 (W/microlitres/min). FIG. 7 shows the representative FTIR/ATR spectrum obtained from both samples.

(30) The FTIR/ATR intensity ratios of peaks attributed to stretching mode of CF.sub.3 and C═O groups, CF.sub.3/C═O, of the coating is indicative of sufficient cross linking in the coating to form a physical barrier. CF.sub.3 refers to the terminal groups in the side chain of PFAC6.

(31) Formation of the barrier coatings is believed to be caused by a mixture of cross linking and controlled fragmentation of the monomers during polymerisation. Cross linking is believed to be predominantly via the CF2-CF3 chain, whilst fragmentation is thought to be predominantly through loss of the C═O group during polymerisation and to a lesser extent shortening of the CF2 chain. Cross linking effects the abundance of —CF3 groups in the coating and controlled fragmentation controls the amount of C═O groups in the coating. The ratio of these two functional groups is an indication that sufficient cross-linking and fragmentation has taken place and can be measured by the ratio of the intensities of the corresponding FTIR/ATR peaks.

(32) It has been shown that coatings with reduced CF.sub.3/C═O ratios give higher resistance values in the electrical test, as described in Example 2, showing an improved coating performance on increased cross linking (for CF.sub.3) and fragmentation (for C═O). If the FTIR/ATR intensity ratio of the peaks attributed to —CF.sub.3 stretching and C═O stretching, CF.sub.3/C═O, is less than 0.6e.sup.−0.1n (where n=6 for PFAC6) the resistance of the coating at the electrical test is expected to be higher than 8 MOhms.

(33) The peak intensity ratio CF.sub.3/C═O the coating thickness and the final current readings during the electrical test are shown in table 2:

(34) TABLE-US-00002 TABLE 2 Resistance in CF.sub.3/C═O Thickness water at 8 V ATR peak (nm) (Ohms) intensity ratio PFAC6 1480 2.1 × 10.sup.7 0.23 PFAC6 and 10% DVA 1450 9.2 × 10.sup.9 0.11 (in volume)