Polymer coatings and methods for depositing polymer coatings

Abstract

A method for protecting a substrate from corrosion, which method comprises in sequence: a first step including plasma polymerization of a precursor monomer and deposition of the resultant polymer onto at least one surface of a substrate; a second step including exposing the polymer to an inert gas in the presence of a plasma without further deposition of polymer onto the or each surface of the substrate; a third step including plasma polymerization of the precursor monomer used in the first step and deposition of the resultant polymer onto the polymer deposited in the first step so as to increase the thickness of the polymer; and optionally, a fourth step including exposing the polymer to an inert gas in the presence of a plasma without further deposition of polymer onto the or each surface of the substrate.

Claims

1. A method of depositing a multi-layer polymer coating having adjacent layers of the same polymer for protecting a substrate from corrosion, which method comprises in sequence: a first step including plasma polymerization of a precursor monomer and deposition of the resultant polymer onto at least one surface of a substrate; a second step including exposing the polymer to an inert gas in the presence of a plasma without further deposition of polymer onto the or each surface of the substrate, wherein the second step improves the water resistance of the polymer deposited in the first step; a third step including plasma polymerization of the precursor monomer used in the first step and deposition of the resultant polymer onto the polymer deposited in the first step so as to increase the thickness of the polymer, wherein the same polymer is deposited in the first step and the third step; and optionally, a fourth step including exposing the polymer to an inert gas in the presence of a plasma without further deposition of polymer onto the or each surface of the substrate, wherein the fourth step improves the water resistance of the polymer deposited in the third step.

2. A method according to claim 1, including repeating the third and fourth steps at least once more.

3. A method according to claim 1, including repeating the third and fourth steps up to ninety nine times.

4. A method according to claim 1, wherein each step including plasma polymerization of the precursor monomer is carried out for a duration that is greater than or equal to the duration of the step(s) including exposing the polymer to an inert gas in the presence of the plasma without further deposition of polymer.

5. A method according to claim 1, wherein the duration of the step(s) including exposing the polymer to an inert gas in the presence of the plasma without further deposition of polymer is from 10 seconds to 20 minutes.

6. A method according to claim 1, wherein the duration of the step(s) including exposing the polymer to an inert gas in the presence of the plasma without further deposition of polymer is from 10 seconds to 1 minute, or from 1 minute to 5 minutes or from 5 minutes to 10 minutes.

7. A method according to claim 1, wherein each step including plasma polymerization of the precursor monomer includes depositing polymer having a thickness from 10 nm to 500 nm.

8. A method according to claim 1, wherein the power of the plasma in the step(s) including exposing the polymer to an inert gas in the presence of the plasma without further deposition of polymer is from 50 Watts to 150 Watts.

9. A method according to claim 1, wherein the inert gas comprises Ar, N.sub.2, He, Ne, Kr, Xe, or a mixture thereof.

10. A method according to claim 1, wherein the precursor monomer is: acrylate, methacrylate, or organosilane.

11. A method according to claim 10, wherein the precursor monomer is hexamethyldisiloxane or an organosilane having one or more alkenyl groups.

12. A method according to claim 11, wherein the or each alkenyl group is a vinyl.

13. A method according to claim 11, wherein the organosilane having one or more alkenyl groups is 1,3-divinyltetramethyldisiloxane.

14. A substrate having a polymer coating formed onto at least one surface thereof according to a method of claim 1.

15. A polymer coating according to claim 14, having a total thickness of 200 nm to 10000 nm.

Description

(1) Embodiments of the invention will now be described, by way of example only, with reference to the accompanying figures.

(2) FIGS. 1A and 1B show schematics of an electrical shortcut test;

(3) FIG. 2 shows a graph comparing (i) PCBs coated with a polymer having a thickness of 400 nm deposited using a conventional method (None); and (ii) PCBs coated with the same polymer as (i) having a thickness of 400 nm deposited using a method according to the invention (Helium);

(4) FIGS. 3A to 3C show graphs comparing (i) PCBs coated with a polymer having a thickness of 2000 nm deposited using a conventional method (No sequence); and (ii) PCBs coated with the same polymer as (i) having a thickness of 2000 nm deposited using a method according to the invention (Stacked);

(5) FIGS. 4A to 4C show graphs comparing (i) PCBs coated with a polymer having a thickness of 5000 nm deposited using a conventional method (No sequence); and (ii) PCBs coated with the same polymer as (i) having a thickness of 5000 nm deposited using a method according to the invention (Stacked);

(6) FIGS. 5A to 5C show graphs comparing (i) PCBs coated with a polymer having a thickness of 8000 nm deposited using a conventional method (No sequence); and (ii) PCBs coated with the same polymer as (i) having a thickness of 8000 nm deposited using a method according to the invention (Stacked);

(7) FIG. 6 shows a graph comparing (i) PCBs coated with a single polymer having a thickness of 1000 nm (no supporting layer); and (ii) PCBs coated with first and second polymer layers having a total thickness of 1000 nm (supporting layer).

(8) To test the performance of coatings an electrical shortcut test was carried out, which involves submersing a substrate—in this case a printed circuit board (PCB)—in water whilst powered.

(9) FIGS. 1A and 1B show the schematic set-up of the electrical shortcut test. Wires 105 and 106 are connected to a PCB 104. The opposite end of wire 105 is connected to a power supply 101 and the opposite end of wire 106 is connected to a multimeter 102, which measures currents in the μA and mA range. Multimeter 102 and power supply 101 are connected through a wire 107. After the circuit has been prepared, the PCB 104 is placed horizontally in water 103. Bottled water is preferred to ensure stability for repeat testing. Alternatively, tap water may be used. The water may have a temperature of from 20° C. to 25° C. The PCB may be submersed to a depth of 5 mm.

(10) The PCB 104 itself may consist of a pair of comb patterns 108, 109. The patterns 108, 109 may be formed from spaced-apart copper tracks 111. The distance between the copper tracks 111 is the so-called“pitch” 110.

(11) Typically, the pitch 110 varies between 0.3 mm and 5.0 mm, which are normal distances used on electronic components. Typically, the copper tracks 111 are between 0.5 mm and 2.0 mm wide.

(12) To start the test, the power supply 101 is turned on at a set value, which remains constant over the whole test duration. Alternatively, a current limitation may be set, which reduces the applied power when a maximal current, e.g. of 60 mA or 180 mA, is reached, to protect the circuit, power supply and multimeter.

(13) The set power value may be chosen as a function of the average, typical, minimal or maximal power that is generated on the electronic device when used. A typical average value for a battery connection of a smartphone is 4.7 V. A typical average value for a camera flash, a charge portal or a touchscreen device may be up to 24 V or higher.

(14) Once the power is turned on via the power supply 101, the current that flows from the copper tracks 111 of one comb structure 108 to the copper tracks 111 of the other comb structure 109 is measured by multimeter 102 and is logged. This current is so-called “shortcut current”, or “short circuiting current”, as it means a current bridge is formed between the two comb patterns 108 and 109, which are separated from each other. In air, the resistance between the copper tracks 111 of comb structures 108 and 109 is very high, so no current is measured.

(15) Damage in the form of corrosion and short circuiting is measured by an increase in current for a given applied voltage, which implies a decrease of resistance over the copper tracks 111 of the comb patterns 108 and 109.

(16) The electrical shortcut test duration is typically up to 20 minutes, such as up to 15 minutes.

(17) Comparison of “No Post Treatment” and “Post Treatment”

(18) A coating was deposited onto a PCB having a pitch of 0.3 mm according to a conventional low pressure polymerisation method (Table 1). The polymer coating has a thickness of 400 nm. The precursor monomer used was an acrylate, namely 1H,1H,2H,2H-Perfluorodecyl acrylate.

(19) TABLE-US-00001 TABLE 1 Conventional method (no post treatment) Parameter Value Plasma Chamber Dimensions 700 × 700 × 1000 mm Temperature wall 30-60° C. Electrodes RF/ground Pre-treatment Gas Argon Flow 300-500 sccm Power 300-600 W Frequency 13.56 MHz Frequency mode Cw Time 5 minutes Coating Monomer 1H,1H,2H,2H-Perfluorodecyl acrylate Flow 25-50 sccm Additional gas — Flow (% of monomer flow) — Base pressure 10-30 mTorr Work pressure 20-75 mTorr Power 40-150 W Frequency 13.56 MHz Frequency mode cw Time 20 minutes

(20) A coating was deposited onto a PCB having a pitch of 0.3 mm according to a low pressure polymerisation method according to the invention (Table 2). The polymer coating had a thickness of 400 nm. The same precursor monomer to the conventional method was used, namely 1H,1H,2H,2H-Perfluorodecyl acrylate. The method according to the invention involved a second step subsequent to the polymerisation step, in which the polymer coating was exposed to Helium in the presence of a plasma (post treatment). The second step did not involve further deposition of polymer onto the PCB, but instead promoted a change in the physical properties of at least the surface of the polymer coating. As mentioned previously, the applicant has discovered that the density of the polymer coating on at least a surface thereof can be increased (without damaging the polymer coating) by exposing the polymer coating to an inert gas in the presence of a plasma.

(21) TABLE-US-00002 TABLE 2 Method according to the invention (post treatment) Parameter Value Plasma Chamber Dimensions 700 × 700 × 1000 mm Temperature wall 30-60° C. Electrodes RF/ground Pre-treatment Gas Argon Flow 300-500 sccm Power 300-600 W Frequency 13.56 MHz Frequency mode cw Time 5 minutes Coating Monomer 1H,1H,2H,2H-Perfluorodecyl acrylate Flow 25-50 sccm Additional gas — Flow (% of monomer flow) — Base pressure 10-30 mTorr Work pressure 20-75 mTorr Power 40-150 W Frequency 13.56 MHz Frequency mode cw Time 20 minutes Post-treatment Gas Helium Flow 50-200 sccm Power 50-150 W Frequency 13.56 MHz Frequency mode cw Time 5-10 minutes

(22) An electrical shortcut test (as described above) was conducted on each coated PCB (i.e. no post treatment and post treatment). The electrical shortcut test was carried out on two PCBs that had been subjected to the method of Table 1 (no post treatment) and two PCBs that had been subjected to the method of Table 2 (post treatment).

(23) FIG. 2 is a plot of the electrical shortcut test data. The current (mA) is shown along the y-axis and time (seconds) is shown along the x-axis.

(24) The measured shortcut current after 900 seconds of water submersion has been recorded in Table 3 for the conventional method (no post treatment) and the inventive method (post treatment). Table 3 shows the average shortcut current measured from the two tests.

(25) The degree of protection of the PCB afforded by the polymer coating is inversely proportional to the measured current. Thus, the lower the current the higher the degree of protection afforded by the polymer coating.

(26) TABLE-US-00003 TABLE 3 Shortcut currents for no post-treatment vs post-treatment; 0.3 mm pitch; 400 nm polymer coating Current (mA) after Post-treatment 900 seconds No 58.3 Yes 20.1

(27) It is clear from Table 3 and FIG. 2 that after 900 seconds submersion, the helium post-treatment results are significantly better than without post-treatment. The effect of the post-treatment is significant even for such a narrow pitch—0.3 mm.

(28) After 900 seconds submersion, the shortcut value for a 0.3 mm pitch PCB with post-treatment and a 400 nm thick coating is 65.5% lower than the shortcut value for a 0.3 mm pitch PCB without post-treatment.

(29) Comparison of “No Post Treatment” and “Repeated Polymerisation/Post Treatment”

(30) 1. Polymer Coating Having a Thickness of 2 μm

(31) 2 μm polymer coatings were deposited onto PCBs having pitches of 0.3 mm, 1.1 mm and 5 mm according to the conventional low pressure polymerisation method (Table 1), with the exception that the coating time was increased from 20 minutes to 100 minutes. The reason for increasing the coating time is that it takes (under the conditions in Table 1) approximately 1 minute to deposit a coating having a thickness of approximately 20 nm. Thus, it follows that it will take approximately 100 minutes to deposit a coating having a thickness of approximately 2 μm. The precursor monomer used was an acrylate, namely 1H,1H,2H,2H-Perfluorodecyl acrylate.

(32) 2 μm polymer coatings were deposited onto PCBs having pitches of 0.3 mm, 1.1 mm and 5 mm according to a low pressure polymerisation method according to the invention (Table 4). The same precursor monomer to the conventional method was used, namely 1H,1H,2H,2H-Perfluorodecyl acrylate. The method according to the invention involved a second step subsequent to the polymerisation step, in which the polymer coating was exposed to Helium in the presence of a plasma (post treatment). The method additionally involved repeating the polymerisation and post-treatment steps a further nine times. In other words, the sequence was (first step:second step)×10.

(33) TABLE-US-00004 TABLE 4 Method according to the invention - repeated polymerisation/post treatment Parameter Value Plasma Chamber Dimensions 700 × 700 × 1000 mm Temperature wall 30-60° C. Electrodes RF/ground Pre-treatment Gas Argon Flow 300-500 sccm Power 300-600 W Frequency 13.56 MHz Frequency mode cw Time 5 minutes Coating Monomer 1H,1H,2H,2H-Perfluorodecyl acrylate Flow 25-50 sccm Additional gas — Flow (% of monomer flow) — Base pressure 10-30 mTorr Work pressure 20-75 mTorr Power 40-150 W Frequency 13.56 MHz Frequency mode cw Time 10 minutes Post-treatment Gas Helium Flow 50-200 sccm Power 50-150 W Frequency 13.56 MHz Frequency mode cw Time 1-5 minutes

(34) An electrical shortcut test was conducted on each coated PCB. The test was carried out twice for the PCBs having 0.3 mm and 1.1 mm pitches and once for the PCBs having a 5.0 mm pitch.

(35) FIGS. 3A (0.3 mm pitch), 3B (1.1 mm pitch) and 3C (5.0 mm pitch) are plots of the electrical shortcut test data.

(36) The measured shortcut currents after 60 seconds and 900 seconds of water submersion have been recorded in Table 5 (0.3 mm pitch), Table 6 (1.1 mm pitch) and Table 7 (5.0 mm pitch) for the conventional method (no post treatment) and the inventive method (which involved repeating polymerisation and post treatment steps). Tables 5 and 6 show the average shortcut current measured from the two tests.

(37) Table 5 to 7 and FIG. 3A to 3C show that a higher degree of protection of the PCB by the polymer coating can be afforded by conducting repeated polymerisation and post treatment steps.

(38) TABLE-US-00005 TABLE 5 Shortcut currents for no post-treatment vs repeated polymerisation/post treatment; 0.3 mm pitch; 2 μm polymer coating Current (mA) after 60 Current (mA) after 900 Post-treatment seconds seconds No 3.3 11.9 Yes 0.21 0.39

(39) TABLE-US-00006 TABLE 6 Shortcut currents for no post-treatment vs repeated polymerisation/post treatment; 1.1 mm pitch; 2 μm polymer coating Current (mA) after 60 Current (mA) after Post-treatment seconds 900 seconds No 4.0 12.9 Yes 0.25 0.41

(40) TABLE-US-00007 TABLE 7 Shortcut currents for no post-treatment vs repeated polymerisation/post treatment; 5.0 mm pitch; 2 μm polymer coating Current (mA) after 60 Current (mA) after Post-treatment seconds 900 seconds No 1.1 12.2 Yes 0.35 0.57

(41) It is clear from Tables 5 to 7 and FIGS. 3A to 3C that after 900 seconds submersion, the repeated polymerisation/post treatment results are significantly better than without post treatment.

(42) For example, after 60 seconds submersion, the shortcut value for a 0.3 mm pitch PCB with a 2 μm thick polymer coating deposited using repeated polymerisation/post treatment steps is 93.8% lower than the shortcut value for a 0.3 mm pitch PCB with a 2 μm thick polymer coating deposited without post treatment.

(43) For example, after 900 seconds submersion, the shortcut value of a 1.1 mm pitch PCB with a 2 μm thick polymer coating deposited using repeated polymerisation/post treatment steps is 96.8% lower than the shortcut value of a 1.1 mm pitch PCB with a 2 μm thick polymer coating deposited without post treatment.

(44) 2. Polymer Coating Having a Thickness of 5 μm

(45) 5 μm polymer coatings were deposited onto PCBs having pitches of 0.3 mm, 1.1 mm and 5 mm according to the conventional low pressure polymerisation method (Table 1), with the exception that the coating time was increased from 20 minutes to 250 minutes to deposit the 5 μm coating. The precursor monomer used was an acrylate, namely 1H,1H,2H,2H-Perfluorodecyl acrylate.

(46) 5 μm polymer coatings were deposited onto PCBs having pitches of 0.3 mm, 1.1 mm and 5 mm according to a low pressure polymerisation method according to the invention (Table 4). The same precursor monomer to the conventional method was used, namely 1H,1H,2H,2H-Perfluorodecyl acrylate. The method according to the invention involved a second step subsequent to the polymerisation step, in which the polymer coating was exposed to Helium in the presence of a plasma (post treatment). The method additionally involved repeating the polymerisation and post-treatment steps a further twenty four times. In other words, the sequence was (first step:second step)×25.

(47) An electrical shortcut test was conducted on each PCB.

(48) FIGS. 4A (0.3 mm pitch), 4B (1.1 mm pitch) and 4C (5.0 mm pitch) are plots of the electrical shortcut test data.

(49) The measured shortcut currents after 60 seconds and 900 seconds of water submersion have been recorded in Table 8 (0.3 mm pitch), Table 9 (1.1 mm pitch) and Table 10 (5.0 mm pitch) for the conventional method (no post treatment) and the inventive method (which involved repeating polymerisation and post treatment steps).

(50) TABLE-US-00008 TABLE 8 Shortcut currents for no post-treatment vs repeated polymerisation/post treatment; 0.3 mm pitch; 5 μm polymer coating Current (mA) after 60 Current (mA) after Post-treatment seconds 900 seconds No 0.44 1.02 Yes 0.02 < 0.1 0.002 < 0.1

(51) TABLE-US-00009 TABLE 9 Shortcut currents for no post-treatment vs repeated polymerisation/post treatment; 1.1 mm pitch; 5 μm polymer coating Current (mA) after 60 Current (mA) after Post-treatment seconds 900 seconds No 0.79 3.57 Yes 0.01 < 0.1 0.03 < 0.1

(52) TABLE-US-00010 TABLE 10 Shortcut currents for no post-treatment vs repeated polymerisation/ post treatment; 5.0 mm pitch; 5 μm polymer coating Current (mA) after 60 Current (mA) after Post-treatment seconds 900 seconds No 0.83 2.52 Yes 5.6E−09 < 0.1 2.02E−05 < 0.1

(53) It is clear from Tables 8 to 10 and FIGS. 4A to 4C that after 900 seconds submersion, the repeated polymerisation/post treatment results are significantly better than without post treatment.

(54) For example, after 60 seconds submersion, the shortcut value of a 0.3 mm pitch PCB with a 5 μm thick polymer coating deposited using repeated polymerisation/post treatment steps is 95.9% lower than the shortcut value of a 0.3 mm pitch PCB with a 5 μm thick polymer coating deposited without post treatment.

(55) For example, after 15 minutes submersion, the shortcut value of a 1.1 mm pitch PCB with a 5 μm thick polymer coating deposited using repeated polymerisation/post treatment steps is 99.2% lower than the shortcut value of a 1.1 mm pitch PCB with a 5 μm thick polymer coating deposited without post treatment.

(56) For the 3 measured pitches—0.3 mm, 1.1 mm and 5.0 mm—the 5 μm thick polymer coating deposited using repeated polymerisation/post treatment steps shows shortcut current values much lower than the limit of visual corrosion (0.1 mA).

(57) 3. Polymer Coating Having a Thickness of 8 μm

(58) 8 μm polymer coatings were deposited onto PCBs having pitches of 0.3 mm, 0.9 mm and 5 mm according to the conventional low pressure polymerisation method (Table 1), with the exception that the coating time was increased from 20 minutes to 400 minutes to deposit the 8 μm coating. The precursor monomer used was an acrylate, namely 1H,1H,2H,2H-Perfluorodecyl acrylate.

(59) 8 μm polymer coatings were deposited onto PCBs having pitches of 0.3 mm, 0.9 mm and 5 mm according to a low pressure polymerisation method according to the invention (Table 4). The same precursor monomer to the conventional method was used, namely 1H,1H,2H,2H-Perfluorodecyl acrylate. The method according to the invention involved a second step subsequent to the polymerisation step, in which the polymer coating was exposed to Helium in the presence of a plasma (post treatment). The method additionally involved repeating the polymerisation and post-treatment steps a further thirty nine times. In other words, the sequence went (first step:second step)×40

(60) An electrical shortcut test was conducted on each PCB.

(61) FIGS. 5A (0.3 mm pitch), 5B (0.9 mm pitch) and 5C (5.0 mm pitch) are plots of the electrical shortcut test data.

(62) The measured shortcut currents after 60 seconds and 900 seconds of water submersion have been recorded in Table 11 (0.3 mm pitch), Table 12 (0.9 mm pitch) and Table 13 (5.0 mm pitch) for the conventional method (no post treatment) and the inventive method (which involved repeating polymerisation and post treatment steps).

(63) TABLE-US-00011 TABLE 11 Shortcut currents for no post-treatment vs repeated polymerisation/ post treatment; 0.3 mm pitch; 8 μm polymer coating Current (mA) after 60 Current (mA) after Post-treatment seconds 900 seconds No 0.40 1.12 Yes 0.002 < 0.1 0.01 < 0.1

(64) TABLE-US-00012 TABLE 12 Shortcut currents for no post-treatment vs repeated polymerisation/ post treatment; 0.9 mm pitch; 8 μm polymer coating Current (mA) after 60 Current (mA) after Post-treatment seconds 900 seconds No 0.63 1.53 Yes 2.19E−06 < 0.1 1.39E−05 < 0.1

(65) TABLE-US-00013 TABLE 13 Shortcut currents for no post-treatment vs repeated polymerisation/ post treatment; 5.0 mm pitch; 8 μm polymer coating Current (mA) after 60 Current (mA) after Post-treatment seconds 900 seconds No 0.25 1.21 Yes 0.001 < 0.1 0.002 < 0.1

(66) It is clear from Tables 11 to 13 and FIGS. 5A to 5C that after 900 seconds submersion, the repeated polymerisation/post treatment results are significantly better than without post treatment.

(67) For example, after 60 seconds submersion, the shortcut value of a 0.3 mm pitch PCB with a 8 μm thick polymer coating deposited using repeated polymerisation/post treatment steps is 99.5% lower than the shortcut value of a 0.3 mm pitch PCB with a 8 μm thick polymer coating deposited without post treatment.

(68) For example, after 900 seconds submersion, the shortcut value of a 0.9 mm pitch PCB with a 8 μm thick polymer coating deposited using repeated polymerisation/post treatment steps is 99.9% lower than the shortcut value of a 0.9 mm pitch PCB with a 8 μm thick polymer coating deposited without post treatment.

(69) For the 3 measured pitches—0.3 mm, 0.9 mm and 5.0 mm—the 8 μm thick polymer coating deposited using repeated polymerisation/post treatment steps shows shortcut current values much lower than the limit of visual corrosion (0.1 mA).

(70) Comparison of “No Supporting Layer” and “Supporting Layer”

(71) A polymer coating was deposited onto a PCB having a pitch size of 1.1 mm according to the parameters and monomer listed in Table 14. The precursor monomer used was a siloxane, namely Hexamethyldisiloxane. The polymer coating had a thickness of 1000 nm and comprised only polyhexamethyldisiloxane (no supporting layer).

(72) TABLE-US-00014 TABLE 14 Conventional method (no supporting layer) Parameter Value Plasma Chamber Dimensions 500 × 400 × 250 mm Temperature wall 30-60° C. Electrodes RF/ground Pre-treatment Gas Argon Flow 10-200 sccm Power 50-300 W Frequency 13.56 MHz Frequency mode cw Time 1-5 minutes Supporting layer None Coating Monomer Hexamethyldisiloxane Flow 5-20 sccm Additional gas Oxygen (O.sub.2) Flow (% of monomer flow) 5-20% Base pressure 10-20 mTorr Work pressure 20-50 mTorr Power 100-300 W Frequency 13.56 MHz Frequency mode cw

(73) A polymer coating was deposited onto a PCB having a pitch size of 1.1 mm according to the parameters and monomers listed in Table 15. The polymer coating comprised a first layer of a polymerised alkene, namely polyethylene, and a second layer of polymerised siloxane, namely polyhexamethyldisiloxane. The first layer had a thickness of approximately 200 nm and the second layer had a thickness of approximately 800 nm, resulting in a total polymer coating having a thickness of approximately 1000 nm.

(74) TABLE-US-00015 TABLE 15 Method according to the invention (supporting layer) Parameter Value Plasma Chamber Dimensions 500 × 400 × 250 mm Temperature wall 30-60° C. Electrodes RF/ground Pre-treatment Gas Argon Flow 10-200 sccm Power 50-300 W Frequency 13.56 MHz Frequency mode cw Time 1-5 minutes Supporting layer Monomer Ethylene Flow 5-20 sccm Power 100-300 W Frequency 13.56 MHz Frequency mode cw Coating Monomer Hexamethyldisiloxane Flow 5-20 sccm Additional gas Oxygen (O.sub.2) Flow (% of monomer flow) 5-20% Base pressure 10-20 mTorr Work pressure 20-50 mTorr Power 100-300 W Frequency 13.56 MHz Frequency mode cw

(75) An electrical shortcut test was conducted on each PCB. The electrical shortcut test was carried out on two PCBs that had been subjected to the method of Table 14 (no supporting layer) and two PCBs that had been subjected to the method of Table 15 (supporting layer).

(76) FIG. 6 shows plots of the electrical shortcut test data.

(77) The measured shortcut currents after 60 seconds and 900 seconds of water submersion have been recorded in Table 16. Table 16 shows the average shortcut current measured from the two tests.

(78) TABLE-US-00016 TABLE 16 Shortcut currents comparing no supporting layer and supporting layer; 1.1 mm pitch; 1000 nm total polymer coating thickness Current (mA) Current (mA) Supporting layer Coating layer after 60 seconds after 900 seconds — 1000 nm 2.1 4.3 200 nm  800 nm 0.11 0.09 < 0.1

(79) It is clear from Table 16 and FIG. 6 that by providing a polyethylene supporting layer beneath the polyhexamethyldisiloxane coating the shortcut currents are significantly lower than the shortcut currents for a single layer of polyhexamethyldisiloxane, which indicates that the polymer coating with supporting layer is more resistant to water than a conventional single layer coating.

(80) For example, after 60 seconds submersion, the shortcut value of the 1.1 mm pitch PCB with a 200 nm polyethylene supporting layer and a 800 nm thick polyhexamethyldisiloxane coating (total coating thickness of 1000 nm) is around 0.1 mA, and is 94.7% lower than the shortcut value of a 1.1 mm pitch PCB without any supporting layer (coating thickness of 1000 nm).

(81) For example, after 900 seconds submersion, the shortcut value of a 1.1 mm pitch PCB with a 200 nm polyethylene supporting layer and a 800 nm thick polyhexamethyldisiloxane coating (total coating thickness of 1000 nm) is below 0.1 mA and is 97.8% lower than the shortcut value of a 1.1 mm pitch PCB without any supporting layer (coating thickness of 1000 nm).

(82) As used herein, the following terms have the following meanings:

(83) “A”, “an”, and “the” as used herein refers to both singular and plural referents unless the context clearly dictates otherwise. By way of example, “a compartment” refers to one or more than one compartment.

(84) “About” or “approximately” as used herein referring to a measurable value such as a parameter, an amount, a temporal duration, and the like, is meant to encompass variations of +/−20% or less, preferably +/−10% or less, more preferably +/−5% or less, even more preferably +/−1% or less, and still more preferably +/−0.1% or less of and from the specified value, in so far such variations are appropriate to perform in the disclosed invention. However, it is to be understood that the value to which the modifier “about” or “approximately” refers is itself also specifically disclosed.

(85) “Comprise,” “comprising,” and “comprises” and “comprised of” as used herein are synonymous with “include”, “including”, “includes” or “contain”, “containing”, “contains” and are inclusive or open-ended terms that specifies the presence of what follows e.g. component and do not exclude or preclude the presence of additional, non-recited components, features, elements, members or steps, known in the art or disclosed therein.

(86) The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within that range, as well as the recited endpoints.

(87) The terms “outgassing” and “degassing”, as used herein, are used interchangeably and refer to a process of removing gases and liquids, more in particular within the context of this document, removing contaminants, gases and liquids from the substrates to be coated, in order to ensure a good adhesion between coating and the exposed surfaces of the substrate.

(88) The term inhibition is defined by a shortcut current value equal to or lower than 0.1 mA (100 μA) for an applied voltage of 4.7 V, when measured in a shortcut test as described further in this document. It has been noticed by the applicants that a shortcut current value equal to or lower than 0.1 mA is the upper limit for visual corrosion. When the maximum shortcut current during the test was equal to or lower than 0.1 mA during the complete test, the tested sample didnt show any signs of corrosion, whereas samples that had values above 0.1 mA did show corrosion spots.

(89) The term substrate as used herein refers to any substrate that comprises electrical circuits or electrical connections or electrical connectors. Examples of substrates are electronic devices, such as smartphones, mobile phones, e-readers, tablets, computers, earphones, headphones, speakers, e.g. portable speakers. Another example of substrates are components of electronic devices, such as one or more printed circuit boards (PCBs), a battery, etc.

(90) References to plasma powers as used herein are based on plasma chambers having a volume of approximately 500 litres and having conventional designs. Adjustment to the plasma power may necessary if the plasma chamber has a larger or smaller volume, or an unconventional design. For instance, the plasma wattage will usually be adjusted to a lower value when a plasma chamber having a volume smaller than 500 litres is utilised. Such adjustments are routine within the field and need not be discussed in detail.