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US5137780.Pdf |||||||||||||| US005137780A United States Patent (19) (11) Patent Number: 5,137,780 Nichols et al. 45) Date of Patent: Aug. 11, 1992 54 ARTICLE HAVING A COMPOSITE Appl. Polym. Sci.: Appl. Polym. Symp., 1984, 38, NSULATIVE COATNG 55-64. Charlson et al., "Electrical Properties of Glow Dis 75 Inventors: Michael F. Nichols; Allen W. Hahn, charge Polymerized Films', Org. Coat. Appl. Polym. both of Columbia, Mo. Sci. Proc., 1982, 47, 146-50. 73) Assignee: The Curators of the University of Hahn et al., "Biocompatibility of Glow Discharge Poly Missouri, Columbia, Mo. merized Films', Org. Coat. Appl. Polym. Sci. Proc., 1982, 47, 386-90. 21 Appl. No.: 439,491 Raschke et al., "Polyparaxylylene Electrets Usable at 22) Filed: Nov. 21, 1989 High Temperatures", J. Appl. Polym. Sci., 1980, 25(8), 1639-44. Related U.S. Application Data Yasuda et al., “Improvement of Blood Compatibility of Membranes by Discharge Polymerization', Am. Chem. 62) Division of Ser. No. 109,079, Oct. 16, 1987, Pat. No. Soc., Div. Org. Coat. Plast. Chem., Pap. 1974, 34(1), 4,921,723. 574-7. (51) Int. Cl. .............................................. B32B 27/08 Lee et al., "Polymer Films for Semiconductor Passiv 52) U.S. Cl. ...................................... 428/336; 427/41; ation. II. Sputtering', Soc. Plast. Eng., Tech. Pap. 1972, 428/411.1; 428/426; 428/446; 428/457; 18 (Pt. 1), 419-23. 428/698 Primary Examiner-Paul J. Thibodeau (58) Field of Search ............... 427/41; 428/411.1, 336, Assistant Examiner-D. S. Nakarani 428/426, 446, 457, 698 Attorney, Agent, or Firm-Senninger, Powers, Leavitt & (56) References Cited Roedel U.S. PATENT DOCUMENTS 57 ABSTRACT 4, 23,308 10/1978 Nowlin et al. ...................... 156/272 A process for applying an adherent electrically insula 4,176,209 11/1979 Baker et al. ......................... 427/248 tive moisture-resistant composite coating to a substrate. 4,291,245 9/1981 Nowlin et al. ...................... 307/400 A thin, adherent, highly cross-linked, substantially liq 4,500,562 2/1985 Jahn et al. ............................. 427/4 uid moisture-impervious primer coating is provided on 4,693,927 9/1987 Nishikawa et al. ................. 428/216 the substrate by glow discharge polymerization of a low molecular weight hydrocarbon monomer in a low pres FOREIGN PATENT DOCUMENTS sure chamber containing the substrate, the monomer 1445546 8/1976 United Kingdom. being selected from among methane, ethane, propane, ethylene, and propylene. A second polymeric coating OTHER PUBLICATIONS layer is provided over the primer coating by glow dis Sharma et al., “Effect of Surface Energetics of Sub charge polymerization of a second precursor compris strates on Adhesion Characteristics of poly-p-xyly ing a hydrocarbon or substituted hydrocarbon. The lenes', J. Adhes., 1982, 13(3-4), 201-14. precursor exhibits a hydrogen yield of not greater than Sharma et al., "Effect of Glow Discharge Treatment of about 0.75 hydrogen atoms per molecule under the Subtrates on Parylene-Substrate Adhesion', J. Vac. glow discharge polymerization conditions under which Sci. Technol., 21(4), Nov./Dec. 1982. the second layer is deposited, whereby the second poly Nichols et al., "Evaluating the Adhesion Characteris meric coating layer is substantially resilient and tics of Glow-Discharge Plasma-Polymerized Films by strongly bonded to the primer coating and the second a Novel Voltage Cycling Technique", J. Appl. Polymer layer comprises a high concentration of surface and Sci.: Applied Polymer Symposium, 38, 21-33 (1984). bulk free radicals. An article produced by the process H. Yasuda, Plasma Polymerization, Academic Press, and an apparatus for carrying out the process are also (1985), pp. 193-194. disclosed. Hahn et al., "Biocompatibility of Glow Discharge Poly merized Films and Vacuum Deposited Parylene', J. 9 Claims, 6 Drawing Sheets SS NAY. ASA O MANYXY /X ZŽ, NSN2222222222 U.S. Patent Aug. 11, 1992 Sheet 1 of 6 5,137,780 NYYYY.M.Ž, Ž Ž-5 9 ZZZZZZZZZZZZ U.S. Patent Aug. 11, 1992 Sheet 2 of 6 5,137,780 /M2/937,7€/ W/77 (x /o/&g U.S. Patent Aug. 11, 1992 Sheet 4 of 6 5,137,780 S NoSN S; 42 Valee/M/6 s 47647 N-AA'44% (2070 (224 (242 (272 Mao A2A 440 A/-2e22ay WAZAAA%WOAe/70/46/46 U.S. Patent Aug. 11, 1992 Sheet 5 of 6 5,137,780 U.S. Patent Aug. 11, 1992 Sheet 6 of 6 5,137,780 4A-7/4 ax/aa //V54472/v (46. AAA, as/2/V Aze 42,47A 57764/472/aas / 7.6 x/24 73 WA2 A/A6 A. 4. (ever 42.445/ew 2a) 2 S.i 2éia (ver 42%.5/ew 42) NS. o,6 A-AA-AA a y A-(AyyyyA dea. A AN 44th -O-O-O-O-O OO-O-O-O-O 42 O-O-O-O-O V 4. 54.06a A se/a47aa7 a Ø 4 a /2 a 20 24 26 77-74 (245) 5,137,780 1. 2 Although parylenes have generally advantageous ARTICLE HAVING A COMPOSITE INSULATIVE electrical, chemical resistance and moisture barrier COATING properties, it has been found that these polymers do not adhere well to many substrate surfaces, particularly The research upon which this application is based under wet conditions. Although these polymers are was supported in part by funds granted by the U.S. quite resistant to liquid water under most conditions, Department of Health and Human Services. they are subject to penetration by water vapor which This is a division of Application Ser. No. 109,027, may condense at the interface between the parylene film filed Oct. 16, 1987, now U.S. Pat. No. 4,921,723. and the substrate, forming liquid water which tends to 10 delaminate the film from the substrate. Vapor deposited BACKGROUND OF THE INVENTION parylene films are also generally quite crystalline and This invention relates to the provision of insulative are subject to cracking which may also create paths for protective coatings on substrates, and more particularly penetration of moisture to the substrate surface. to a novel process for providing a tough, thin, adherent, Substantial efforts have been made in the art to devise insulative coating that constitutes a barrier against pene 15 means for pre-treating a substrate to enhance adherence tration of liquid water and ions to the surface of the to subsequently applied parylene. Other work has re substrate. lated to the treatment of a pre-formed parylene film to Numerous applications require protection of a sub improve its adhesiveness to another surface to which it strate against contact with liquid water, ions or ioniz is subsequently mated. able species. In many mechanical or electrical devices, 20 One factor which has reportedly affected the adher contact of the surface with moisture may cause galvanic ence of parylene is the hydrophobicity of the substrate. corrosion. In electrical devices such as integrated cir Certain of the work previously conducted in this art has cuits, protection of the substrate surface from moisture involved plasma treatment of the substrate, which has may be essential to prevent the generation of stray cur been found to render the substrate more susceptible to rent paths which may result in short-circuiting of the 25 adhesion of subsequently applied vapor deposited pary device. lene. As found, for example by Sharma et al., "Effect of Insulative or other protective materials which work Surface Energetics of Substrates on Adhesion Charac well in dry air are often inadequate in high humidity or teristics of Poly-p-xylylenes". J. Adhes., 1982, 13(3-4). liquid environments. Both corrosion and electrical 201-14, glow discharge treatment of a glass surface breakdown problems are exacerbated if a device is ex 30 with an argon or methane plasma reduces the surface posed to water that contains inorganic ions. One partic energy and leaves the substrate surface in a hydropho ularly difficult and sensitive application of integrated bic condition. Sharma et al. suggest the application of a circuits, semiconductors and metal electrodes is in elec glow discharge polymerized methane primer coating to trical or electronic device implantation in a human or the substrate prior to vapor deposition of the poly-p- animal body. Extra-cellular fluids within the body are 35 xylylene. They also investigated preliminary glow dis saline, and often contain a number of other ions or other charge treatment of the surface with either argon or electrolytes. At body temperatures, severe and rapid oxygen, but found treatment with methane plasma to be corrosion may lead to rapid and untimely failure of the the most effective. Oxygen plasma treatment was found device. Short of corrosive failure, the operation of the to render the surface hydrophilic and was detrimental device may be disturbed by stray currents in a manner to adhesion. In the course of Sharma et al.'s experimen which can, in some instances, be catastrophic to the tal work, the walls of the reactor became coated with host. parylene and some of this material was sputtered off and Various materials have been developed to provide an deposited on the substrate during plasma treatment. electrically insulative moisture barrier over a substrate. However, this effect was reported to be much less pro Among the more prominent of these are aromatic polyi 45 nounced during treatment with methane than with ar mides such as those sold under the trade designation gon. "Kevlar" by E.I. DuPont de Nemours, & Co. However, Sharma et al, "Effect of Glow Discharge Treatment polyimides must be applied by wet processes such as of Substrates on Parylene-Substrate Adhesion', J. Vac. deposition from organic solution, requiring the han Sci. Technol, 21 (4), Nov./Dec. 1982 also describes the dling, recycle, and/or disposal of organic solvents, and 50 pretreatment of metal and glass surfaces with argon, thus implicating the materials cost, environmental con oxygen or methane plasma prior to the vapor deposition trol, and capital and operating costs that attend solvent of poly-p-xylylene.
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