WO2002031027A1 - Coating composition - Google Patents

Coating composition Download PDF

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Publication number
WO2002031027A1
WO2002031027A1 PCT/US2001/031907 US0131907W WO0231027A1 WO 2002031027 A1 WO2002031027 A1 WO 2002031027A1 US 0131907 W US0131907 W US 0131907W WO 0231027 A1 WO0231027 A1 WO 0231027A1
Authority
WO
WIPO (PCT)
Prior art keywords
coating composition
coating
resin
added
solid content
Prior art date
Application number
PCT/US2001/031907
Other languages
French (fr)
Inventor
Abbas A. Sadriwalla
Original Assignee
Wireless Raincoat, Inc.
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Wireless Raincoat, Inc. filed Critical Wireless Raincoat, Inc.
Priority to AU2002213153A priority Critical patent/AU2002213153A1/en
Publication of WO2002031027A1 publication Critical patent/WO2002031027A1/en

Links

Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05K—PRINTED CIRCUITS; CASINGS OR CONSTRUCTIONAL DETAILS OF ELECTRIC APPARATUS; MANUFACTURE OF ASSEMBLAGES OF ELECTRICAL COMPONENTS
    • H05K3/00—Apparatus or processes for manufacturing printed circuits
    • H05K3/22—Secondary treatment of printed circuits
    • H05K3/28—Applying non-metallic protective coatings
    • H05K3/285—Permanent coating compositions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
    • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
    • B23K35/3612—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest with organic compounds as principal constituents
    • B23K35/3613—Polymers, e.g. resins
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D175/00—Coating compositions based on polyureas or polyurethanes; Coating compositions based on derivatives of such polymers
    • C09D175/04—Polyurethanes
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D183/00—Coating compositions based on macromolecular compounds obtained by reactions forming in the main chain of the macromolecule a linkage containing silicon, with or without sulfur, nitrogen, oxygen, or carbon only; Coating compositions based on derivatives of such polymers
    • C09D183/04—Polysiloxanes
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
    • B23K35/02—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape
    • B23K35/0222—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by mechanical features, e.g. shape for use in soldering, brazing
    • B23K35/0244—Powders, particles or spheres; Preforms made therefrom
    • B23K35/025—Pastes, creams, slurries

Definitions

  • the invention relates to a water resistant coating composition made from a combination of urethane, acrylic and silicone resins, and for the use of such coating as a conformal coating on printed circuit boards to protect the circuit boards from shorting or corrosion due to exposure to water or non-corrosive liquids.
  • the coating composition is manufactured as bulk liquid which can be incorporated into spray can format if desired.
  • the coating composition can also be manufactured as part of a solder paste. Upon exposure to heat, the metal particles in the solder paste sinter, causing the coating composition to be exuded from the paste, to encapsulate the fused colder with non-conductive , non- corrosive coating.
  • Epoxy resin can be added to the coating composition or solder paste, to provide greater adhesive qualities if desired.
  • the coating composition described herein was developed after specifically seeking a coating with strong water repellence, but which could be applied as a thin, even coat so as to offer uniform coverage with easy application. Through extensive formulations trial and error, it was surprisingly found that the best results for creating a truly water repellant coating were achieved with a combination of urethane, acrylic and silicone resins as identified herein. There has not previously been a coating with solid content composed of significant parts of urethane resin, acrylic resin and silicone resin combined together into a single chemical composition.
  • Acrylated-urethane products are available, which offer fast curing times under UV exposure, and provide somewhat better protection than acrylic alone, but such combination does not significantly improve upon the limited water resistance provided by urethane alone.
  • the difficulty with current conformal coatings are that they fail to provide other than simple moisture resistance for limited exposure.
  • the coating composition described herein was developed to provide not just limited moisture resistance, but full protection to the printed circuit board from exposure to water or salt-water spray, and even complete immersion for limited periods, without permanent damage or corrosion.
  • Many of the currently available coatings including the acrylated- urethane are difficult to rework or remove, and those that can be easily reworked provide very little protection.
  • the coating composition described herein can be worked through for repairs, and if necessary is easily removed with chemicals, without damaging the board. Parylene is difficult to apply, as it requires the boards being placed in a special vacuum container. Extensive and detailed masking of the board is also required, as parylene is applied as a gas, and permeates indiscriminately into every area that the gas can reach. The fact that none of the available coatings provide sufficient water resistance was identified as the basis for Patent No.
  • the coating composition described herein combines urethane, acrylic and silicone resins to form a novel chemical, which can be used to create a uniform coating on printed circuit boards or other surfaces, which coating is highly resistant to water, salt water and other non- corrosive liquids.
  • the surface to be protected is cleaned sufficiently to remove any dirt and dust, and to clear away any oils or grease left - from individuals handling the boards or other sources.
  • the surfaces must be protected from additional contamination during the application of the coating.
  • the coating composition identified herein is non-conductive , those areas of the printed circuit board, or other surface to be coated, that are to remain conductive, must be masked before application.
  • the coating composition is applied by dipping, brushing or spraying, so that the entire surface is uniformly coated with 1.5 mil to 2 mil thick coating.
  • Both sides of the printed circuit board should be coated, and then permitted to air cure for 36 hours. A quicker curing time can be provided with use of a heat source, provided that such heat will not damage any of the components being coated.
  • the coating is thin and will flow over the surface of the printed circuit board, covering all components attached thereto.
  • the coating which contains a UV tracer will glow under UV light to assist in determining if the entire board is sufficiently coated.
  • the coating composition should also provide a water repellant coating for surfaces other than printed circuit boards , provided that the surfaces are of a material that the coating can adhereto .
  • the coating composition of claim 1 (a) is comprised of 10-15% solids, comprised of:
  • Printed circuit boards to be coated must be removed from their housings. Where possible plastic parts should be detached to prevent possible damage from solvents. Use of facemask and safety glasses is highly recommended.
  • Used circuit boards may have existing corrosion due to prior exposure to water or other liquids .
  • the process of cleaning may further weaken or damage corroded areas. Therefore it is essential to test the device and conduct repairs as necessary to ensure proper function of the unit before commencing the steps of masking and spraying.
  • LCD's, copper contact surfaces, connectors, battery terminals , switches or any surface that needs to remain conductive must be properly masked before spraying. These components are generally found on communication devices such as pagers and cell phones. Other electronic devices will need masking of appropriate surfaces . Failure to properly mask may result in component and/or device failure since the protective coating is non- conductive. Overspray can be cleared off by scrubbing gently with a fine wire brush or scraping with a sharp tool such as a razor blade.
  • the actual thickness per spray is operator dependent and will dictate the number of coatings required and the ultimate thickness of the coating.
  • Portable ultra violet fluorescent lights sometimes referred to as black lights, are available at lighting or hardware stores.
  • the coating composition containing a UV tracer is used, so that it will glow in the dark in the presence of UV light. Insufficient coating or missed areas can be corrected with addiional spraying.
  • the sprayed side should be tack free in 15 to 20 minutes. Spray the opposite side of the circuit board using the steps outlined above. If the boards are sprayed in an ambience with high humidity the coating composition will show a blushing effect (haziness or opacity) . This condition is easily eliminated by heating the coated assembly in an oven for 30 minutes at 170 degrees F.
  • Full cure of the coating composition requires a minimum 24 hours, however, 36 hours is recommended for optimal cure.
  • the treated circuit boards may be reassembled into their cases once they are tack free and prior to reaching full cure. Care must be taken not to damage or penetrate the film in the assembly process. Curing will continue within the housings but at a lightly slower rate.

Landscapes

  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Materials Engineering (AREA)
  • Wood Science & Technology (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Mechanical Engineering (AREA)
  • Non-Metallic Protective Coatings For Printed Circuits (AREA)
  • Paints Or Removers (AREA)

Abstract

A water repellant coating composition, comprised of a combination of urethane resin, acrylic resin and silicone resin, with the remaining solids content being comprised of the usual aromatic solvents and suspension agents belonging to chemicals in the acetate, butane, propylene, ketone and toluene families. The coating can be air cured and is also curable by IR or other heat source.

Description

COATING COMPOSITION Field of the Invention
The invention relates to a water resistant coating composition made from a combination of urethane, acrylic and silicone resins, and for the use of such coating as a conformal coating on printed circuit boards to protect the circuit boards from shorting or corrosion due to exposure to water or non-corrosive liquids.
The coating composition is manufactured as bulk liquid which can be incorporated into spray can format if desired.
The coating composition can also be manufactured as part of a solder paste. Upon exposure to heat, the metal particles in the solder paste sinter, causing the coating composition to be exuded from the paste, to encapsulate the fused colder with non-conductive , non- corrosive coating.
Epoxy resin can be added to the coating composition or solder paste, to provide greater adhesive qualities if desired. BACKGROUND OF THE INVENTION
As more electronic equipment is being used in outdoor environments, such as handheld wireless communication devices, automobile electronics, marine electronics, avionics, computers, toys, etc., a large number of devices with printed circuit boards are exposed to condensation, water spray, water immersion or beverages .
A group of coatings generically known as conformal coatings, have been available to provide some additional moisture resistance to printed circuit boards. There are basically five categories of these coatings, being acrylic resin, urethane resin, silicone resin, exposy resin and parylene . The coating composition described herein was developed after specifically seeking a coating with strong water repellence, but which could be applied as a thin, even coat so as to offer uniform coverage with easy application. Through extensive formulations trial and error, it was surprisingly found that the best results for creating a truly water repellant coating were achieved with a combination of urethane, acrylic and silicone resins as identified herein. There has not previously been a coating with solid content composed of significant parts of urethane resin, acrylic resin and silicone resin combined together into a single chemical composition. Acrylated-urethane products are available, which offer fast curing times under UV exposure, and provide somewhat better protection than acrylic alone, but such combination does not significantly improve upon the limited water resistance provided by urethane alone. The difficulty with current conformal coatings , are that they fail to provide other than simple moisture resistance for limited exposure. However, during the use of pagers, cellular phones and other portable electronic devices, the threat of exposure to rain and other liquids requires much greater water repellants . The coating composition described herein, was developed to provide not just limited moisture resistance, but full protection to the printed circuit board from exposure to water or salt-water spray, and even complete immersion for limited periods, without permanent damage or corrosion.
A necessary feature for any coated boards used by professionals, is the ability to rework the board to repair or replace components, when necessary. Many of the currently available coatings including the acrylated- urethane are difficult to rework or remove, and those that can be easily reworked provide very little protection. The coating composition described herein can be worked through for repairs, and if necessary is easily removed with chemicals, without damaging the board. Parylene is difficult to apply, as it requires the boards being placed in a special vacuum container. Extensive and detailed masking of the board is also required, as parylene is applied as a gas, and permeates indiscriminately into every area that the gas can reach. The fact that none of the available coatings provide sufficient water resistance was identified as the basis for Patent No. 6,127,038, which provides for a secondary coating to be applied to a printed circuit board after first applying a coating of acrylic, urethane, silicone, epoxy or parylene. This secondary coating is for the purpose of offering additional protection from water damage that is not provided by the currently available coatings . Summary of the Invention
The coating composition described herein combines urethane, acrylic and silicone resins to form a novel chemical, which can be used to create a uniform coating on printed circuit boards or other surfaces, which coating is highly resistant to water, salt water and other non- corrosive liquids. As an initial step, the surface to be protected is cleaned sufficiently to remove any dirt and dust, and to clear away any oils or grease left - from individuals handling the boards or other sources. The surfaces must be protected from additional contamination during the application of the coating. As the coating composition identified herein is non-conductive , those areas of the printed circuit board, or other surface to be coated, that are to remain conductive, must be masked before application.
The coating composition is applied by dipping, brushing or spraying, so that the entire surface is uniformly coated with 1.5 mil to 2 mil thick coating.
Both sides of the printed circuit board should be coated, and then permitted to air cure for 36 hours. A quicker curing time can be provided with use of a heat source, provided that such heat will not damage any of the components being coated.
The coating is thin and will flow over the surface of the printed circuit board, covering all components attached thereto. The coating which contains a UV tracer will glow under UV light to assist in determining if the entire board is sufficiently coated.
After the board has fully cured, and is reassembled in the appropriate device, such board will not short circuit, or corrode when exposed or immersed in water or non-corrosive liquids. The coated board will continue to function even if receiving electrical power at the time of such water exposure or immersion, as the coating is non-conductive. The coating composition should also provide a water repellant coating for surfaces other than printed circuit boards , provided that the surfaces are of a material that the coating can adhereto . Detailed Description of the Preferred Embodiment
The description is of the preferred embodiment of te invention, and is not intended in any way to limit the applications for which the coating composition identified herein may be used.
The coating composition of claim 1 (a) is comprised of 10-15% solids, comprised of:
(al) 20-45 urethane resin (a2) 20-45% acrylic resin (a3) 20-45% silicone resin
Printed circuit boards to be coated must be removed from their housings. Where possible plastic parts should be detached to prevent possible damage from solvents. Use of facemask and safety glasses is highly recommended.
Surfaces to be coated must be thoroughly cleaned of dirt, grease, flux residue and all similar contaminants for successful application of coating. Use cleaning agents such as isopropyl alcohol for light cleaning or lacquer thinner for more entrenched grime. A soft bristle brush may be used to facilitate cleaning. Cleaned boards must be protected from re-contamination. Use latex gloves during handling to prevent transfer of dirt or body oils which may impede good adhesion.
Used circuit boards may have existing corrosion due to prior exposure to water or other liquids . The process of cleaning may further weaken or damage corroded areas. Therefore it is essential to test the device and conduct repairs as necessary to ensure proper function of the unit before commencing the steps of masking and spraying.
LCD's, copper contact surfaces, connectors, battery terminals , switches or any surface that needs to remain conductive must be properly masked before spraying. These components are generally found on communication devices such as pagers and cell phones. Other electronic devices will need masking of appropriate surfaces . Failure to properly mask may result in component and/or device failure since the protective coating is non- conductive. Overspray can be cleared off by scrubbing gently with a fine wire brush or scraping with a sharp tool such as a razor blade.
Set up the parts to be sprayed on a tabletop and preferably in a wood or cardboard tray for ease of handling. Use proper ventilation.
Hold the can 8" to 12" from the object being sprayed and lean it in about 10 to 15 degrees. Use steady and smooth left to right strokes. Spraying the PC board from each of its four edges constitutes one spray cycle and will ensure proper coverage with the coating composition. Complex components like IC ' s should be first sprayed individually so that good coverage is achieved on leads and edges. Then proceed with the spraying of the board in general.3 to 4 spray cycles are required to achieve a 1.5 mil minimum to a 2 mil optimum coating which in turn will provide the basic to most effective protection.
Allow 3 to 5 minutes between coatings. The actual thickness per spray is operator dependent and will dictate the number of coatings required and the ultimate thickness of the coating. Check and make sure that the necessary coating has been applied and no vital areas have been left unprotected. This can be done by viewing the board in a darkened area and in the presence of an ultra violet light source. Portable ultra violet fluorescent lights, sometimes referred to as black lights, are available at lighting or hardware stores. The coating composition containing a UV tracer is used, so that it will glow in the dark in the presence of UV light. Insufficient coating or missed areas can be corrected with addiional spraying. The sprayed side should be tack free in 15 to 20 minutes. Spray the opposite side of the circuit board using the steps outlined above. If the boards are sprayed in an ambience with high humidity the coating composition will show a blushing effect (haziness or opacity) . This condition is easily eliminated by heating the coated assembly in an oven for 30 minutes at 170 degrees F.
Full cure of the coating composition requires a minimum 24 hours, however, 36 hours is recommended for optimal cure. The treated circuit boards may be reassembled into their cases once they are tack free and prior to reaching full cure. Care must be taken not to damage or penetrate the film in the assembly process. Curing will continue within the housings but at a lightly slower rate.
Exposure to harsh environments prematurely may result in damage or permanent failure of the device. Those skilled in the arts will adjust the proportion of urethane resin, acrylic resin and silicone resin contained in the composition, within the parameters set forth therein, to suit specific applications.

Claims

What is claimed is:
1. A coating composition comprising:
(a) from 10-25% of the solid content being a combination of :
(al) 10-75% urethane resin (a2) 20-75% acrylic resin (a3) 10 to 75% silicone resin
(b) with the remaining solids content being comprised of the standard aromatic solvents and suspension agents belonging to chemicals in the acetate, butane, benzene, xylene, ketone and toluene families.
2. The coating composition of claim 1, packaged in a spray can with the use of standard propellants.
3. The coating composition of claim 1, added to a solder powder, with the solder powder comprisng 70% to 97% of the solid content, and the coating composition of claim 1 comprising 20 to 30% of the solid content, with fluxing agent added if necessary.
4. The coating composition of claim 1, with an epoxy resin added, the epoxy resin being 1 to 10% of the combination described in claim 1(a).
5. Applying the coating composition of claim 1 to a printed circuit board by brushing, dipping or spraying, after first cleaning the board of dust, dirt and oils, and applying the coating to a thickness of from 1.5 mil to 2 mils, although a thicker coating can be used to provide additional protection and to enhance shock.
6. The coating composition of claim 1, using lower or no solvent content, to produce a low VOC coating composition.
7. The coating composition of claim 1, with a UV trader added to identify areas covered by the coating.
PCT/US2001/031907 2000-10-12 2001-10-12 Coating composition WO2002031027A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2002213153A AU2002213153A1 (en) 2000-10-12 2001-10-12 Coating composition

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US68996000A 2000-10-12 2000-10-12
US09/689,960 2000-10-12

Publications (1)

Publication Number Publication Date
WO2002031027A1 true WO2002031027A1 (en) 2002-04-18

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Application Number Title Priority Date Filing Date
PCT/US2001/031907 WO2002031027A1 (en) 2000-10-12 2001-10-12 Coating composition

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AU (1) AU2002213153A1 (en)
WO (1) WO2002031027A1 (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103436154A (en) * 2013-09-04 2013-12-11 安徽华东光电技术研究所 Conformal coating formula and conformal coating usage method
CN106280937A (en) * 2016-08-30 2017-01-04 乐凯特科技铜陵有限公司 A kind of waterproof anti-corrosion three-proofing coating used for printed circuit board and preparation method thereof

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5085364A (en) * 1989-09-05 1992-02-04 Senju Metal Industry Co., Ltd. Pressure-sensitive adhesive for temporarily securing electronic devices
US5215601A (en) * 1991-04-17 1993-06-01 Yuho Chemicals Inc. Additive for fluxes and soldering pastes
US5294459A (en) * 1992-08-27 1994-03-15 Nordson Corporation Air assisted apparatus and method for selective coating
US5820697A (en) * 1997-04-18 1998-10-13 International Business Machines Corporation Fluorescent water soluble solder flux
US5871822A (en) * 1996-09-26 1999-02-16 Honeywell Inc. Low emissions method for spray application of conformal coating to electronic assemblies
US6127038A (en) * 1997-12-11 2000-10-03 American Meter Company Printed circuit board coating and method

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5085364A (en) * 1989-09-05 1992-02-04 Senju Metal Industry Co., Ltd. Pressure-sensitive adhesive for temporarily securing electronic devices
US5215601A (en) * 1991-04-17 1993-06-01 Yuho Chemicals Inc. Additive for fluxes and soldering pastes
US5294459A (en) * 1992-08-27 1994-03-15 Nordson Corporation Air assisted apparatus and method for selective coating
US5871822A (en) * 1996-09-26 1999-02-16 Honeywell Inc. Low emissions method for spray application of conformal coating to electronic assemblies
US5820697A (en) * 1997-04-18 1998-10-13 International Business Machines Corporation Fluorescent water soluble solder flux
US6127038A (en) * 1997-12-11 2000-10-03 American Meter Company Printed circuit board coating and method

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103436154A (en) * 2013-09-04 2013-12-11 安徽华东光电技术研究所 Conformal coating formula and conformal coating usage method
CN106280937A (en) * 2016-08-30 2017-01-04 乐凯特科技铜陵有限公司 A kind of waterproof anti-corrosion three-proofing coating used for printed circuit board and preparation method thereof

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