Process for depositing copper layers on shaped articles of a polyimide
United States Patent Brandt et al.  
 14 1 Apr. 29, 1975 PROCESS FOR DEPOSITING COPPER LAYERS ON SHAPED ARTICLES OF A POLYIMIDE [75] Inventors: Wilhelm Brandt, Wertach; lrmgard Bindrum, Wiesbaden-Biebrich. both of Germany [73] Assignee: Kalle Aktiengesellschaft,  
 Wiesbaden-Biebrich. Germany [22] Filed: Dec. 5, 1972 [21] Appl. N0.: 312,272  
 [30] Foreign Application Priority Data Decv 8. 1971 Germany 2160821 [52] US. Cl 428/458; 204/38 B; 427/306 [51} Int. Cl B44d 1/02 [58] Field of Search 117/47 A, 138.8 N. 160 R 156] References Cited UNITED STATES PATENTS 3.403.035 9/1968 Schneblc. Jr. et a1. 1 17/47 A 3.544.432 12/1970 lshii et al. 117/47 A Primary Examiner-Cameron K. Weiffenbach Attorney, Agent, or Firnz.lames E. Bryan [57] ABSTRACT This invention relates to a process for depositing a copper layer on a surface of a shaped article of a polyimide, which process comprises a. treating the surface with a solution of a noble metal salt and a halogenated alkanoic acid, and then drying the surface at an elevated temperature,  
 b. treating the surface with a solution including a reducing agent but which does not include a halogenated alkanoic acid,  
 steps (a) and (b) being carried out in either order, and then c. treating the surface with a solution containing a copper salt and a reducing agent.  
 25 Claims, No Drawings PROCESS FOR DEPOSITING COPPER LAYERS ON SHAPED ARTICLES OF A POLYIMIDE The invention relatesto a process for depositing copper layers on shaped articles of a polyimide.  
  It is known to provide shaped articles of electrically non-conductive plastics, for example polystyrene, acrylonitrile-butadiene-styrene copolymers (ABS plastics), polyolefms and polyesters, if necessary after a suitable pre-treatment, with thin metal coatings, the coating being carried out non-electrolytically or electrolytically. A coating process that has proved particularly successful involves depositing a very thin layer of noble metal nuclei on the plastic surface by sensitizing the surface with a noble metal salt solution and activating it with the solution of a reducing agent. Coherent metal layers then can be deposited on the noble metal nuclei by means of chemical or electrolytic metallization baths. The sensitizing pretreatment can be carried out, for example, by first treating the surface with a palladium salt solution, for example PdCland then with a hydrazine hydrate solution, whereupon small amounts of elemental palladium are deposited on the surface.  
  In order to anchor the metal layers subsequently to be applied, so that they adhere firmly, it is customary to roughen the plastic surface mechanically or, preferably, chemically, before the pre-treatment step described above. In the case of ABS plastics the chemical roughening may be effected, for example, with concentrated sulfuric acid which additionally can contain an oxidizing agent.  
  Copending application Ser. No. 207,966, filed Dec. 14, 1971, provides a process for depositing a metal layer on a surface of a shaped article of a polyester, which process comprises a. sensitizing the surface with a noble metal salt solution,  
 b. activating the surface with a reducing agent, and  
 c. chemically metallizing the surface with a metal salt solution, e.g. a copper salt solution,  
 steps (a) and (b) being carried out in either order. The first of the steps (a) and (b) or each of both steps or at least step (a) is carried out with a solution additionally containing a halogenated alkanoic acid, preferably trichloroacetic acid, and, immediately after treatment with the solution containing halogenated alkanoic acid, the shaped article is dried with heating.  
  If the metallizing processes hitherto known are applied to the copper plating of polyimide shaped articles, firmly adhering coatings are not obtained.  
  The present invention provides a process for depositing a copper layer on a surface of a shaped article of a polyimide, which process comprises a. treating the surface with a solution which comprises a noble metal salt and a halogenated alkanoic acid, and then drying the surface at an elevated temperature,  
 b. treating the surface with a solution which comprises a reducing agent but does not include a halogenated alkanoic acid,  
 steps (a) and (b) being carried out in either order, and then c. treating the surface with a solution comprising a copper salt and a reducing agent.  
 The invention makes it possible to provide shaped articles of polyimides with a firmly adhering copper coat- Polyimides which can be provided with a copper coating by the process of the invention include essentially all high molecular weight condensation products of aromatic diamines with dianhydrides of aromatic tetracarboxylic acids. Examples of suitable aromatic diamines are 4,4&#39;-diamino-dipheny-propane, 4,4- diamino-diphenylmethane, benzidine, 4,4&#39;-diaminodiphenylsulfide, 4,4&#39;-diamino-diphenylsulfone, 4,4- diamino-diphenyl-ether, m-phenylene-diamine, and pphenylenediamine. Suitable dianhydrides are, for example, the dianhydrides of the following tetracarboxylic acids: 2,3,6,7-naphthalene tetracarboxylic acid, 3,3&#39;,4,4&#39;-diphenyl tetracarboxylic acid, bis-(3,4-dicarboxy-phenyl)-propane, bis-(3,4-dicarboxy-phenel)- ether and pyromellitic acid.  
  The halogenated alkanoic acid is advantageously a chlorinated acetic acid, preferably trichloroacetic acid. However, it is also possible to use other halogenated alkanoic acids, for example 2,2,3-trichloropropionic acid or trifluoroacetic acid.  
  The treatment solution which contains the haloge nated carboxylic acid preferably contains water as the solvent. The solvent, however, also may consist of one or more organic liquids, for example acetone or butanone, or may be a mixture of one or more organic liquids with water.  
  The amount of halogenated alkanoic acid, especially trichloroacetic acid, in the noble metal salt solution can vary very greatly. In general, solutions of about 5 to 25% by weight, preferably 10 to 15% by weight, are used.  
  Noble metal salts which may be used include the salts of platinum, palladium, gold or silver. Palladium chloride, which may be present in concentrations of between 0.001 and 5% by weight, preferably between 0.005 and 0.5% by weight, is preferred.  
  The reducing agent is preferably tin-ll chloride, but it is also possible&#39;to use an organic reducing agent, for example hydrazine hydrate. Tin-ll chloride may be used in aqueous solution containing hydrochloric acid, the concentration of the tin-ll chloride preferably being between 0.1 and 10% by weight, advantageously 0.5 to 5% by weight. Hydrazine hydrate may be used inalkaline aqueous solution, advantageously in concentrations of between 0.1 and 5% by weight, preferably of 0.5 to 1% by weight.  
  The noble metal salt solution and the reducing agent solution may be allowed to act on the polyimide at room temperature for 10 seconds to 10 minutes, perferably 30 seconds to 3 minutes.  
  Before the sensitization or activation of the polyimide shaped articles, the latter are preferably subjected to a cleaning process or surface hydrolysis in order to achieve uniform wetting by the treatment solution. Cleaning can be effected in a known manner with an organic solvent, or with an acid, or alkali. A particularly suitable agent for treating the surface is an aqueous solution which contains 1 to 5% by weight of chromic acid, 30 to 60% by weight of phosphoric acid and 30 to 50% by weight of sulfuric acid. The bath temperature is preferably between 50and C and the period of action is advantageously 5 to 15 minutes. After the treatment the acid is rinsed off and the chromic acid which still adheres to the surface of the polyimide molding may be removed with an alkaline sodium thiosulfate solution. This avoids an uncontrolled local rection of the noble metal salt with remaining chromic acid when the sensitizing solution is applied.  
  Shaped articles which may be copper plated by the process of the invention include all types of rigid polyimide moldings, for example those manufactured by injection molding. [t is, however, also possible to plate flexible shaped articles, for example fibers, filaments and films of polyimides by the process of the invention. The process of the invention is of particular advantage for the production of copper plated films, which find extensive industrial use, since naturally the adhesion of a metal layer presents a greater problem in the case of flexible films than in the case of rigid moldings.  
  A substance which improves the wettability is preferably added, in known manner, to all the treatment solutions described above in order to achieve as uniform an action as possible. In order to achieve constant wetting even during the drying process a small amount, for example 0.01 to 2%, of a water-soluble substance of high molecular weight, for example polyvinyl alcohol, also may be added to the solution which contains the halogenated carboxylic acid. The content of wetting agent in the solution can in general be about 0.1 to 5% by weight. If a hydrazine hyrdrate or tin-ll chloride solution is used as the activating solution, it is not necessary to add a wetting agent to this solution.  
  After application of the sensitizing solution containing the halogenated alkanoic acid the molding is dried at elevated temperature. During drying it is important that the temperature of the treated surface should not exceed 150C when a palladium salt solution containing a halogenated carboxylic acid is used; in general, a temperature of 120to 130C is used. The drying should not take place too rapidly since apparently a certain period of action of the treatment solution at elevated temperature is necessary if good adhesion of the copper layer to the substrate is to be obtained. The drying time is preferably 1 to 3 minutes, advantageously about 2 minutes. The drying can be carried out in hot air but also can take place under infrared radiators, for example.  
  After deposition of noble metal nuclei on the surface of the polyimide shaped article the copper can be deposited non-electrolytically on the surface from a copper salt bath containing reducing agents, i.e,, the surface is chemically metallized.  
  When a copper layer thickness of the order of magnitude of 0.2 to 0.3 am has been reached, any desired further thickening of the copper layer can be effected electrolytically or again non-electrolytically, in known manner.  
  Electroplating baths with or without the addition of levelling and polishing agents are suitable for the electrolytic thickening of approximately 0.2 to 0.3 um thick copper layers deposited according to the invention. The deposition of copper in the electrolytic baths may be carried out at current densities of between 0.1 and 2 A/square decimeter. The electrolytically depos ited copper layers together with the nonelectrolytically deposited layer underneath adhere firmly to the polyimide substrate.  
  The conditions and procedures for the metallizing steps described are in themselves known and do not form part of the present invention.  
  Using the process according to the invention, firmly adhering copper layers can be applied to a part of the surface or to the entire surface of the shaped article.  
 Thus films, for example, can be copper plated on one side or on both sides.  
  The adhesion of the copper layer to the substrate increases in the initial period after deposition of the metal and reaches its final maximum value after 1 to 3 days. The copper layers obtained according to the invention adhere so firmly to the substrate that, even if the copper plated shaped articles are stored for weeks in an atmosphere saturated with water vapor, their good adhesion is retained.  
  If a polyimide shaped article is subjected to the same treatment process as a shaped article treated by the process of the invention but without addition of a halogenated alkanoic acid to the noble metal salt solution, either no copper deposition takes place at all in the non-electrolytic bath (if the film has first been treated with palladium chloride and then with reducing agent), or copper deposition does take place in a nonelectrolytic bath (if the film has first been treated with reducing agent and then with palladium chloride), but after thickening of the non-electrolytically deposited layer in an electrolytic bath the thickened copper layer can be easily removed from the substrate. 1n the latter case the adhesion of the electrolytically thickened layers declines greatly within three days in air saturated with water vapor.  
  Because of the extremely good heat resistance of polyimide films, copper plated polyimide films made by the process of the invention can be used, for example, for the manufacture of printed circuits. Printed circuits may be made from films which have been electrolytically thickened with copper or from the films which carry only the non-electrolytically deposited thin copper layer.  
  The following Examples further illustrate the invention. Unless otherwise stated, percentages are by weight.  
 EXAMPLE 1 A pm thick polyimide film of a polycondensate of diamino-diphenyl-ether and pyromellitic dianhydride was immersed for 7 minutes in an aqueous solution warmed to 70C which contained 1.7% of chromic acid, 49.0% of phosphoric acid, 40.0% of sulfuric acid and 9.3% of water as well as 0.005% of perfluorooctane carboxylic acid as the wetting agent.  
  The film was then sprayed with water for 1 minute and immersed for 5 minutes in an aqueous solution, warmed to 40C, which contained 3% of sodium hydroxide and 1% of sodium thiosulfate.  
  The film was again sprayed with water for 1 minute and was then immersed for 30 seconds at room temperature in an aqueous solution which contained 0.15% of palladium chloride, 0.25% of hydrogen chloride, 0.5% of polyvinyl alcohol of K-value 30 and 12% residual acetyl group content (Mowiol N 30-88 of Farbwerke Hoechst AG), 0.4% of sodium dodecylbenzene sulfonate and 13% of trichloroacetic acid.  
  The treated film was fired for 2 minutes at C. The dried film was immersed for 30 seconds at room temperature in an aqueous solution which contained 0.6% of hydrazine hydrate and 1.25% of sodium hydroxide. The film was sprayed down and introduced for 2 minutes into a non-electrolytic copper bath warmed to 49C which had the following composition:  
 6.2 g of CuSOrS H O 0.1 g ofNiSO4 H 5 g of formaldehyde 8.5 g of sodium hyposulfite 3.5 g of sodium hydroxide 6 g of sodium tartrate 8.5 g of N.N.N&#39;.N&#39;-tctra-(Z-hydroxypropyl)- ethylenediamine. and 0.25 g of the ethylene oxide adduct of isopropanol. made up to l liter with water.  
  A 0.29 am thick copper layer was deposited on the film surface. When a cross-pattern of fine lines spaced about 1 mm apart was scratched in this layer by means of a razor blade and a pressure-sensitive adhesive tape was stuck over the pattern, no copper was removed from the substrate when the adhesive tape was abruptly pulled off.  
  The copper layer was thickened to am over the course of 3 hours in an electrolytic bath having the composition shown below. The bath was at room temperature and l A per square decimeter current density was used.  
 Bath Composition:  
 250 g of CuSO 5 H 0 g of sulfuric acid (98% cone.) made up to l liter with water.  
  A stripping force for stripping the copper layer from the polyimide film (1 cm wide film strip) could not be measured in the peel test according to DIN 40,802 since when an attempt was made to separate the copper film from the polyimide film the latter plit before the copper layer tore.  
  Similarly, an electrolytically deposited copper layer only l0 pm thick could not be detached from the substrate.  
 in an aqueous solution which contained 0.15% of palladium chloride, 0.25% of hydrogen chloride, 0.5% of polyvinyl alcohol as in Example 1, 0.4% of sodium dodecylbenzene sulfonate and 13% of trichloroacetic acid. The treated film was dried for 2 minutes at 130C. The film was then immersed in the copper bath of Example l, warmed to 49C, for 2 minutes.  
 The thickness of the copper layer was 0.24 am. The  
 0 layer adhered inseparably in the adhesive tape experiment described in Example 1.  
  Electrolytic thickening of this layer was carried out as in Example 1 until a layer thickness of 30 82 m was reached.  
  As in Example 1, the force for pulling off the copper layer could not be measured.  
  When the electrolytically deposited copper layer was only 10 pm thick, it could not be detached from the substrate.  
 EXAMPLE 3 8 polyimide films were treated in the manner described in Examples 1 and 2.  
  The Table shows the test results for different sequences of the sensitizing solution (a) and the reducing solution (b) with and without the addition of trichloroacetic acid (TCA) to the solutions (a) and (b).  
  A copper deposition in a non-electrolytic copper bath (0.2 to 0.3 pm) and adhesion of the nonelectrolytically deposited copper layer.  
  B thickening of the layer A to 10 am in an electrolytic copper bath and adhesion of the electrolytically thickened copper layer.  
  It can be seen from the Table that good adhesion is obtained only if the trichloroacetic acid is added only to the palladium chloride solution.  
 TABLE Experiment lst Step 2nd Step A B l Palladium chloride Tin-ll chloride or No Cu deposit hydrazine hydrate ll Tin-ll chloride or Palladium chloride Cu deposit more or Separablc hydrazine hydrate less separable Ill Palladium ehloridc/TCA Tin-II chloride or Cu deposit inseparable lnseparable hydrazone hydrate IV Tin-ll chloride or Palladium chloride/T CA Cu deposit inseparable lnscparable hydrazine hydrate V Palladium chloride Tinll chloride/TCA No Cu deposit Vl Tin ll chloride/T CA Palladium chloride Cu deposit separable Separable Vll Palladium chloride/TCA Tin-ll chloride/TCA No Cu deposit Vlll Tin-ll chloride/T C A Palladium chloride/&#39;1&#39; CA Cu deposit separable Separable An inseparable adhesion is thus achieved only if trichloroacetic acid is added only to the palladium chloride solution.  
 EXAMPLE 2 A film as specified in claim I, which had been degreased and rinsed with alkaline sodium thiosulfate solution exactly as in Example 1. was activated for 5 minutes at room temperature in an aqueous solution which contained 0.5% by weight of tin-ll chloride and 0.7% by weight of hydrogen chloride.  
 I The film was sprayed down with water for 1 minute and then immersed for 30 seconds at room temperature It will be obvious to those skilled in the art that many modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.  
 What is claimed is:  
  l. A polyimide film having on its surface a copper layer which cannot be separated from said surface by mechanical means.  
 2. A process for depositing a copper layer on a surface of a shaped article of a polyimide, which process comprises a. treating the surface with a solution ofa noble metal salt and ,about to 25% by weight of a halogenated alkanoicacid, and then drying the surface at a temperatu re in the range of about 120to 130C.  
 b. treating the surface with a solution including a reducing agent but which does not include a halogenated alkanoic acid, steps (a) and (b) being carried out in either order, and then c. treating the surface with a solution containing a copper salt and a reducing agent.  
  3. A process as claimed in claim 2, wherein &#39;an aqueous solution of the noble metal salt and the halogenated alkanoic acid is used.  
  4. A process as claimed in claim 2, wherein the concentration of the acid is 10 to by weight.  
  5. A process as claimed in claim 2, whereinthe drying is carried out for a period of from 1 to 3 minutes.  
  6. A process as claimed in claim 2, wherein each of the treatment solutions used in steps (a) and (b) contains a wetting agent.  
  7. A process as claimed in claim 2, wherein the solution used in step (a) contains about 0.01 to 2% by weight polyvinyl alcohol.  
  8. A process as claimed in claim 2, wherein each of the treatments of steps (a) and (b) is carried out for a period of from 10 seconds to 10 minutes.  
  9. A process as claimed in claim 2, wherein the surface to be treated has previously been cleaned or subjected to surface hydrolysis.  
 . 10. A process as claimed in claim 2, wherein, after step&#39; (c). the thickness of the layer of copper is increased by electrolytic deposition of copper on the existing layer.  
  11. A process as claimed in claim 2, wherein the polyimide is a condensation product of at least one aromatic diamine with at least one aromatic tetracarboxylic acid dianhydride.  
  12. A process as claimed in claim 2, wherein the shaped article is an injection-molded article.  
  13. A process as claimed in claim 2, wherein the shaped article is a film. I  
  14. A process as claimed in claim 2, wherein the halogenated alkanoic acid is a chlorinated acetic acid.  
  15. A process as claimed in claim 14, wherein the acid is trichloracetic acid.  
  16. A process as claimed in claim 2, wherein the drying is carried out at a temperature not greater than 150C.  
  17. A process as claimed in claim 16, wherein the temperature is l20to C.  
 18. A process as claimed in claim 2, wherein the reducing agent in step (b) is tin-llchloride.  
 19. A process as claimed in claim 18, wherein the solution used in step (b) is an aqueous solution, containing hydrochloric acid, of tin-ll chloride, the concentration of the tin-ll chloride being between 0.1 and 10% by weight.  
  20. A process as claimed in claim 2, wherein the reducing agent is hydrazine hydrate.  
  21. A process as claimed in claim 20, wherein the solution used in step (b) is an alkaline aqueous solution of hydrazine hydrate, the concentration of the hydrazine hydrate being between 0.1 and 5% by weight.  
  22. A process as claimed in claim 2, wherein the noble metal salt is a salt of platinum, palladium, gold or silver.  
  23. A process as claimed in claim 22, wherein the salt is palladium chloride.  
  24. A process as claimed in claim 23, wherein the solution used in step (a) contains 0.001 to 5% by weight of palladium chloride.  
 25. A process as claimed in claim 24, wherein the concentration is 0.005 to 0.5% by weight.  
  UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3 3,881,049  
 DATED 1 April 29, 1975 INVENTOR(S) I Wilhelm Brandt and Irmgard Bindrum It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:  
  Item should read: &#34;Hoechst Aktiengesellschaft, Frankfurt/Main, Germany&#34; Column 2, line 6, &#34;dipheny-&#34; should read diphenyl Line 14, &#34;phenel)-&#34; should read phenyl) Column 5, line 2, &#34;0.1 g of NiSO -H 0&#39;&#39; should read 0.1 g of NiSO 71-1 0 Line 32, &#34;plit&#34; should read split Column 6, line 12, &#34;82&#34; should read p Signed and Scaled this twenty-ninth D3) Of July 1975 [SEAL] A trest:  
 RUTH- C. M AHSON C. MARSHALL DANN Arresting ()jjrzer (ummissimzcr nflarents and Trademarks