GB2572591A

GB2572591A - PCB separator sheet

Info

Publication number: GB2572591A
Application number: GB1805560.8A
Authority: GB
Inventors: Frank Mitchell Stephen; Hamilton Sheila
Original assignee: M2H Industries Ltd
Current assignee: M2H Industries Ltd
Priority date: 2018-04-04
Filing date: 2018-04-04
Publication date: 2019-10-09
Also published as: GB201805560D0

Abstract

A printed circuit board (PCB) separator 5 (i.e. a slip sheet or interleaving sheet) comprising a polymeric film 10; wherein an anti-static material or additive 15 is disposed on or in the polymeric film and/or the polymeric film is or comprises an electrically conductive polymer. The anti-static material 20 may comprise carbon nanostructured material, e.g. carbon nanotubes. The anti-static material 20 may be dispersed within a body or matrix 25 of the polymeric film or it may be a coating on the polymeric film. The PCB separator 5 may be embossed and/or otherwise provided with 3D patterning on at least one planar surface thereof. Also disclosed is a method of producing a PCB separator sheet 5 comprising disposing an anti-static material or additive 15 on or in a polymeric film 10. Further disclosed is a method of using the above PCB Separator Sheet 5, the method comprising providing the PCB separator sheet on a PCB or between PCBs.

Description

PCB Separator Sheet

FIELD

Described herein are PCB separator sheets, also known as slip sheets or interleaving sheets, and associated methods of producing and using such sheets.

BACKGROUND

Separator sheets, also known as slip sheets or interleaving sheets are commonly used in the printed circuit board (PCB) manufacturing industry to protect PCB boards, e.g. to prevent scratching, mechanical handling damage and oxidation and to prevent airborne dust from landing on the PCB.

The most common type of PCB separator sheet is formed from paper. However, over time, the paper breaks up resulting in dust and contamination. Paper also absorbs moisture, which is undesirable as PCB manufacturers try to eliminate moisture from their boards.

To avoid this, it is known to use plastic sheets as PCB separators. However, these plastic sheet PCB separators generate a lot of static electricity. This is not an issue for many applications. However, the tracks on boards are generally becoming thinner and also functional components are being embedded with the printed circuit boards. Such functional components can be easily be damaged by static discharges.

SUMMARY

Various aspects of the present invention are defined in the independent claims. Some preferred features are defined in the dependent claims.

According to a first aspect of the present disclosure is a PCB separator comprising:

a substrate, such as a polymeric film; and an anti-static material or additive is disposed on or in the substrate; and/or the substrate is an electrically conductive polymer film.

The anti-static material may be or comprise a nanomaterial. The anti-static material may be or comprise particles such as nanoparticles. The anti-static material may have an average particle size or maximum particle size in the order of nanometres, e.g. between 1 and 500nm, such as between 10 and 120nm, for example, between 50 and 100 nm.

The anti-static material may be or comprise an electrically conducting material. The antistatic material may be or comprise a carbonaceous material. The anti-static material may be or comprise an open and/or 3D structured or porous material. The anti-static material may be or comprise a nanostructured material, such as nanotubes. The anti-static material may be or comprise a carbon nanostructured material, e.g. carbon nanotubes. The nanotubes may be single walled nanotubes.

The anti-static material may be dispersed within the polymeric film, e.g. within a body or matrix of the polymeric film. The anti-static material may be provided within the polymeric film at a concentration of at least 0.1% w/w. The anti-static material may be provided within the polymeric film at a concentration of at least 0.1% w/w but less than 40%, e.g. less than 20%, such as less than 10% w/w, e.g. so that the polymeric film may retain suitable processability and handling properties. The anti-static material may be evenly or uniformly dispersed within the polymeric film or may be dispersed within the polymeric film with a varying concentration or having a concentration gradient, e.g. through the thickness of the film. For example, the concentration of anti-static material may be greater at or towards one or more or each surface (e.g. planar surface) of the polymeric film than in the core or centre of the polymeric film.

The anti-static material may be provided in a coating on the polymeric film. The coating may be electrically conducting, e.g. due to the anti-static material. The anti-static material may be coated or otherwise disposed onto one, both or each surface of the polymeric film. For example, the polymeric film may comprise opposing planar surfaces and the anti-static material may be provided in a coating on one or both planar surfaces. The coating may comprise the anti-static material dispersed in a coating matrix. The anti-static material may be provided in the coating at a concentration of at least 0.1% w/w. The coating matrix may be a polymeric matrix. The coating may comprise at least 20%w/w, e.g. at least 50% or at least 70% w/w of the coating matrix. The coating matrix may be, or comprise one or more of, an acrylic, polyurethane and/or epoxy. The coating may be or comprise an anti-static coating.

The coating comprising the anti-static material and/or the polymeric film having the anti-static material dispersed in it and/or the electrically conductive polymeric film and/or the PCB separator as a whole may have a surface resistance of less than 10¹² Ohms, e.g. less than 10⁹Ohms, such as less than 10⁷ Ohms.

The coating may be retro-coated onto the polymeric material. The coating may be applied by gravure coating, reverse gravure coating, doctor blade, dip coating and/or the like.

By providing the anti-static material either locked into the matrix of the polymeric film or embedded into the coating matrix of the coating on the polymeric film, shedding of the antistatic material is reduced or prevented. Shedding of the anti-static material may otherwise cause short circuits or contamination of the PCB or result in false readings with certain PCB inspection tests.

The coating may be a black or other dark coloured coating, e.g. which may be due to the anti-static material being carbonaceous, e.g. carbon nanotubes or other nanostructures. The polymeric film may be of a contrasting colour to the coating, e.g. the polymeric film may be a white or other light colour. In this way, when the anti-static coating is starting to wear thin, the polymeric film will become visible through the thin parts of the coating to provide a visual alert, e.g. to allow an operator to replace the PCB separator film.

The coating and/or the polymeric film may be embossed and/or otherwise provided with 3D patterning, e.g. on one or both of the planar surfaces. This may improve the anti-stick I separation properties of the PCB separator.

The polymeric film may be or comprise a polyolefin film, such as polypropylene or polyethylene film.

The polymeric film and/or the PCB separator sheet may have a thickness (e.g. a dimension perpendicular to the planar direction) of greater than 200pm, e.g. between 200 and 750pm, such as between 200 and 500pm. In this way, the PCB separator may provide sufficient self-support and/or rigidity. If the PCB separator is too thick or too thin, then there may be handling issues, but the above thicknesses may result in beneficial handling properties.

According to a second aspect of the present disclosure is a method of producing a PCB separator sheet comprising disposing an anti-static material or additive disposed on or in a substrate, such as a polymeric film.

The anti-static material may be a nanomaterial. The anti-static material may be provided as nanoparticles. The anti-static material may have an average particle size or maximum particle size in the order of nanometres, e.g. between 1 and 500nm, such as between 10 and 120nm, for example, between 50 and 100 nm.

The anti-static material may be or comprise an electrically conducting material. The antistatic material may be or comprise a carbonaceous material. The anti-static material may be or comprise an open structured or porous material. The anti-static material may be or comprise a nanostructured material, such as nanotubes. The anti-static material may be or comprise a carbon nanostructured material, e.g. carbon nanotubes. The nanotubes may be or comprise single walled nanotubes.

The method may comprise dispersing the anti-static material within the polymeric film, e.g. within a body or matrix of the polymeric film. The method may comprise forming the polymeric film with the anti-static material disposed within the polymeric film, e.g. by extruding, casting, bubble-blowing or otherwise forming a film from a feedstock comprising a polymeric material having the anti-static material dispersed within.

The method may comprise evenly dispersing the anti-static material within the polymeric film. The method may comprise dispersing the anti-static material within the polymeric film with a varying concentration or having a concentration gradient, e.g. through the thickness of the film. For example, the method may comprise providing a greater concentration of antistatic material at or towards one or more or each surface (e.g. planar surface) of the polymeric film than in the core or centre of the polymeric film.

The method may comprise coating or otherwise disposing a coating comprising the antistatic material onto one, both or each surface of the polymeric film. For example, the polymeric film may comprise opposing planar surfaces and the method may comprise providing a coating comprising the anti-static material on one or both planar surfaces. The coating may comprise the anti-static material dispersed in a coating matrix. The coating may be or comprise an anti-static coating. The coating may be electrically conductive, e.g. by virtue of the anti-static material.

The method may comprise retro-coating the coating comprising the anti-static material onto the polymeric material. The method may comprise applying the coating by gravure coating, reverse gravure coating, doctor blade, dip coating and/or the like.

The method may comprise providing a black or other dark coloured coating, e.g. which may be due to the anti-static material being carbonaceous, e.g. carbon nanotubes or other nanostructures. The method may comprise providing a polymeric film that is of a contrasting colour to the coating, e.g. the polymeric film may be a white or other light colour.

The method may comprise embossing and/or otherwise 3D patterning the coating and/or the polymeric film, e.g. on one or both of the planar surfaces.

The PCB separator film may be the PCB separator film of the first aspect.

According to a third aspect of the present disclosure is a method of using the PCB separator sheet of the first aspect, the method comprising providing the PCB separator sheet on a printed circuit board (PCB) or between printed circuit boards.

According to a fourth aspect of the present disclosure is an assembly comprising a printed circuit board (PCB) and the PCB separator sheet of the first aspect, the PCB separator sheet being provided on the PCB.

The individual features and/or combinations of features defined above in accordance with any aspect of the present invention or below in relation to any specific embodiment of the invention may be utilised, either separately and individually, alone or in combination with any other defined feature, in any other aspect or embodiment of the invention.

Furthermore, the present invention is intended to cover apparatus configured to perform any feature described herein in relation to a method and/or a method of using, producing or manufacturing any apparatus feature described herein. For any of the apparatus features described above as performing a function, the present invention also covers a method comprising performing that function.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present disclosure will now be described, by way of example only, with reference to the accompanying Figures, in which:

Figure 1 is a schematic cross section of a PCB separator film;

Figure 2 is a schematic cross section of an alternative PCB separator film;

Figure 3 is a schematic cross section of a further alternative PCB separator film;

Figure 4 is a schematic cross section of a yet further alternative PCB separator film;

Figure 5 is a schematic of another alternative PCB separator film; and

Figure 6 is a schematic of an assembly of a PCB separator film, such as any of those of Figures 1 to 5, and a PCB.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 shows an embodiment of a PCB separator 5 comprising a polymeric film 10 that has been coated on one side with an electrically conductive anti-static coating 15. The polymeric film 10 could be a polyolefin film, such as polypropylene or polyethylene film. In an example, the polymeric film 10 is at least 200pm thick, e.g. having a thickness between 200 and 500pm. This may provide suitable self-supporting and handling qualities for the separator 5.

The coating generally comprises an electrically conductive antistatic material 20 embedded within a coating matrix 25. The coating matrix 25 is optionally a polymeric or resin matrix, typically being formed of a different polymer to that of the polymeric film 10. For example, the polymeric film could be a polypropylene, polyethylene or other polyolefin film or a copolymer thereof. As examples, the coating matrix could be an acrylic, polyurethane or epoxy. The coating contains the electrically conductive anti-static material 20 in sufficient quantities so that a desired surface resistance or conductivity of the coating is achieved, e.g. at least 0.1 % with respect to weight (w/w). For example, a surface resistance for the coating material of less than 10⁹Ω would be suitable for many applications.

For example, the conductive coating 15 could be formed by dispersing the material for forming the coating matrix 25 with the electrically conductive material 20 in water or other suitable solvent and then coating it onto the polymeric film using a suitable coating technique such as gravure, reverse gravure, doctor blade, dip coating and/or the like.

In an embodiment, the antistatic material 20 may be a carbonaceous powder. In a specific example, the antistatic material 20 is in the form of a 3D structured or nanostructured carbon material such as carbon nanotubes. It has been found that this provides particularly effective anti-static properties along with advantageously low particulate loss. However, it will be appreciated that other electrically conductive materials could be used instead.

In an embodiment, the coating 15 is of a contrasting colour to the polymer film 10. For example, the coating 15 could be black or another dark colour and the polymer film 10 could be white or another light colour. In this way, it may be easy to visually identify when the conductive coating 15 is wearing thin, in use.

Optionally, the polymeric matrix 25 could be or comprise a conductive polymer. If a suitably conductive material is used for the coating 15, then the conductive anti-static coating 15 could, in certain embodiments, simply consist of the conductive material (e.g. a conductive polymer or some other suitable conductive material), without having the anti-static conductive material 20 dispersed within it. However, coatings in the form of a metallic layer could be disadvantageous as these could cause a sudden discharge. The coating 15 / coating matrix 25 would need to have suitable properties to allow it to adhere to the polymeric film 10.

In the example of Figure 1, the PCB separator 5 would be applied to the PCB such that the conductive anti-static coating 15 faces towards I contacts the PCB so as to provide the required anti-static properties. The example of Figure 2 comprises an electrically conductive anti-static coating 15 on both sides of the polymeric film 10. This provides improved antistatic properties at the expense of additional cost.

The provision of a conductive antistatic coating 15, e.g. of conductive material 20 within a polymeric coating matrix 25, or as a conductive polymer or other suitable conductive material may beneficially reduce shedding of electrically conductive anti-static material as the coating 15 suitably adheres to the polymeric film 10 and locks in the conductive antistatic material 20.

Another example of a PCB separator 305 is shown in Figure 3. In the PCB separator 305 of Figure 3, an electrically conductive antistatic material 320 is embedded within the polymer matrix of a polymer film 310. The electrically conductive antistatic material 320 is optionally carbon nanotubes provided in a concentration sufficient to impart the polymeric film 310 with a suitable conductivity and/or surface resistance. Again, a suitable surface resistance is less than 10⁹Ω and a suitable thickness range for the polymer film 310 is greater than 200pm thick, e.g. having a thickness between 200 and 500pm.

In the example of Figure 3, the electrically conducting antistatic material 320 is uniformly distributed throughout the polymeric film 310. For example, the electrically conducting antistatic material 320 could be mixed with the polymeric feedstock used to form the polymeric film 310 before the feedstock is used to form the polymeric film 310, resulting in a polymeric film 310 having the conductive antistatic material 320 already embedded within.

However, it will be appreciated that the distribution of electrically conducting antistatic material 320 need not be uniform, e.g. the concentration of electrically conducting material 320 may vary across the thickness of the polymeric film 310. In an example as shown in Figure 4, the concentration of electrically conducting material 320 is greater at or towards the surface of the polymeric film 310 relative to the core.

It will be appreciated that the above examples are not definitive and that variations or any combination of the features of the above examples of Figures 1 to 4 could be used. For example, Figure 5 shows an example of a PCB separator 505 comprising a polymeric film 510 having conductive antistatic material 520 embedded within it and dispersed throughout it and with an additional electrically conductive antistatic coating 515 provided on at least one surface.

In another example, the polymeric film could be or comprise an inherently electrically conductive film formed from an electrically conductive polymer, e.g. having a surface resistance less than 10⁹Ω. Examples of electrically conductive polymer include (but are not limited to) polyacetylene, polyphenylene vinylene, polypyrole, polythiopene, polyaniline, polyphenylene sulphide and/or copolymers thereof.

In use, regardless of which example of PCB separator 5, 305, 505 described above (or variation thereof) is used, in use, the PCB separator 5, 305, 505 is provided on a PCB 630, as shown in Figure 6 so as to protect the PCB from scratching, mechanical handling damage and oxidation and to reduce dust and other particulate from landing on the PCB.

Although specific examples are described above in relation to the Figures, it will be appreciated that variations on the above examples are possible. As such, the scope of protection is defined by the claims and not by the above specific examples.

For example, although the present invention is escribed above in relation to a polymeric film 10, the principles described herein are also applicable to substrates other than the polymeric film 10. Furthermore although carbon nanotubes are advantageously used in the above examples, it will be appreciated that other electrically conductive materials could be used.

Although various examples of polymeric films 10 and coating matrices 25 are described above, other polymers or other materials could be used.

Claims

1. A PCB separator comprising:

a polymeric film; and wherein an anti-static material or additive is disposed on or in the polymeric film; and/or the polymeric film is or comprises an electrically conductive polymer.

2. The PCB separator of claim 1 wherein the anti-static material comprises nanoparticles.

3. The PCB separator of claim 2, wherein the anti-static material is or comprises a carbon nanostructured material, e.g. carbon nanotubes.

4. The PCB separator of any preceding claim, wherein the anti-static material is dispersed within a body or matrix of the polymeric film.

5. The PCB separator of claim 4, wherein the anti-static material is evenly or uniformly dispersed within the polymeric film.

6. The PCB separator of claim 4, wherein the anti-static material is dispersed within the polymeric film with a varying concentration, or having a concentration gradient through the thickness of the film.

7. The PCB separator of any preceding claim, wherein the anti-static material is provided in a coating on the polymeric film.

8. The PCB separator of claim 7, wherein the coating comprises the anti-static material dispersed in a coating matrix.

9. The PCB separator of any preceding claim, having a surface resistance of less than 109Ohms.

10. The PCB separator of claim 7 or any claim dependent thereon, where the polymeric film is of a contrasting colour to the coating.

11. The PCB separator of claim 10, wherein the coating is black and the polymeric film is white.

12. The PCB separator of any preceding claim, wherein eh PCB separator is embossed and/or otherwise provided with 3D patterning on at least one planar surface thereof.

13. The PCB separator of any preceding claim, wherein the polymeric film is a polyolefin film.

14. The PCB separator of any preceding claim, wherein the PCB separator has a thickness of greater than 200pm.

15. The PCB separator of claim 14, wherein, the PCB separator has a thickness of between 200 and 750pm.

16. A method of producing a PCB separator sheet comprising disposing an anti-static material or additive on or in a polymeric film.

17. A method of using the PCB separator sheet of any of claims 1 to 15, the method comprising providing the PCB separator sheet on a printed circuit board (PCB) or between printed circuit boards.

18. An assembly comprising a printed circuit board (PCB) and the PCB separator sheet of any of claims 1 to 15, the PCB separator sheet being provided on the PCB.