Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23F—NON-MECHANICAL REMOVAL OF METALLIC MATERIAL FROM SURFACE; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL; MULTI-STEP PROCESSES FOR SURFACE TREATMENT OF METALLIC MATERIAL INVOLVING AT LEAST ONE PROCESS PROVIDED FOR IN CLASS C23 AND AT LEAST ONE PROCESS COVERED BY SUBCLASS C21D OR C22F OR CLASS C25
  • C23F1/00—Etching metallic material by chemical means
  • C23F1/10—Etching compositions
  • C23F1/14—Aqueous compositions
  • C23F1/16—Acidic compositions
  • C23F1/18—Acidic compositions for etching copper or alloys thereof

Definitions

• the present invention concerns a process for etching the portions of the copper printed circuits which are not protected by printing ink.
• an insulating backing is first provided with a copper coating 35 or 70 m. thick which is then printed with an etch resistant printing ink on the portions which should be retained as conductor lines after the etching.
• the etching is effected by spraying the printed plates with an etching liquid or by dipping such printed plates in an etching bath in order to dissolve the copper which is not protected by the printed resist. 5
• Usual etching liquids are strong mineral acids such as H 50, and HNO as well as chromic acid, iron chloride or ammonium persulfate solutions. The use of such solutions, however, entail certain disadvantages.
• ammonium persulfate While several disadvantages could be avoided by the 4 use of ammonium persulfate, its use still has several drawbacks. As ammonium persulfate only attacks the copper slowly, it is necessary to add activators or the solution is activated with heat. In spite of this the'etching periods necessary, even though not very great, are still longer than those required from iron chloride. Ammonium persulfate solutions can only effectively be used in a concentration range of 150 to 250 g./liter of water. Therefore the capacity of such solutions for take up of Cu is correspondingly smaller than when iron chloride solutions are employed. The recovery of copper from the spent ammonium persulfate solutions is somewhat simpler than from spent iron chloride or chromic acid solutions. It, for example, can be effected by cementation with aluminum or by electrolysis, nevertheless the removal of the remaining ammonium ions requires additional measures.
• dilute H 80 or HNO only attack ggppgr slowly they do not come into consideration for etching printed circuits where complete dissolution in the shortest e possible is equired. It is Ffiwhrongh addition or an oxidi i5 ent such as, H or other peroxygen compo tfig sii ch amsilmr perborates that dissolgtion of copper can be accelerated when dilute mineral acids 3153 551. 'BathsTif' mafia have been suggested in the literature for the surface treatment of metals especially for polishing such surfaces. See
• H 0 activated mineral acid baths could be successfully used for etching printed circuits when certain definite requirements are met.
• the essence of the process according to the invention resides in the use of aqueous H 0 containing mineral acid solutions which in addition contain urea or functional urea derivatives, as stabilizers, for the etching of printed circuits.
• etching velocity is to be accelerated still further this can effectively be accomplished by the addition of other activators, namely, salts of heavy metals which are more noble than copper, such as, for example, Hgcl
• activators namely, salts of heavy metals which are more noble than copper, such as, for example, Hgcl
• the activating effects ,Iof r such heavy metal salts are known in connection with etching processes with ammonium persulfate.
• the etchiiirg baths according to the invention possess sufficient stability for use in the etching process although it was to be expected that an accelerated decomposition of the bath would take place.
• HgCl solution (6.8 g. HgCl /l. corr. to 5 p.p.m.
• the aqueous mineral acid solutions by weight expediently contain 15%-10%, preferably, 3.5%7.0% of H (100%), 1%-15% of urea or functional urea derivative, preferably, 3%-7% of urea and 1 p.p.m.-50 p.p.m., preferably, p.p.m.-10 p.p.m. of heavy metal salt activator.
• the etching solution should contain 1.54 g. H 80 per 1 g. of copper.
• the content of sulfuric acid within the etching solution is between about 0.01 and about 0.7 kg. per liter of the solution, preferably between about 0.1 and about 0.2 kg.
• a mineral acid solution consisting essentially of water, 0.01 to 0.7 kilogram per liter of sulfuric acid or phosphoric acid, 1.5 to 10% H 0 and 1 to of a stabilizer for the H 0 selected from the group consisting of urea, semicarbazide, biurct. barbituric acid and dipropyl barbituric acid.
• the mineral acid is sulfuric acid and the solution also contains 1 to 50 p.p.m. of a heavy metal salt wherein the heavy metal is selected from the group consisting of silver, mercury, rhodium and platinum and the salt is a chloride, nitrate or sulfate.

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Citations (8)

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• 1964
  • 1964-08-22 DE DED45262A patent/DE1255443B/de active Pending
• 1965
  • 1965-07-31 FR FR26819A patent/FR1442847A/fr not_active Expired
  • 1965-08-17 BE BE668424D patent/BE668424A/xx unknown
  • 1965-08-17 GB GB35244/65A patent/GB1055009A/en not_active Expired
  • 1965-08-18 US US480775A patent/US3463733A/en not_active Expired - Lifetime
  • 1965-08-20 NL NL6510927A patent/NL6510927A/xx unknown

Patent Citations (8)

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