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
• • 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
  • C23F1/32—Alkaline compositions
  • C23F1/34—Alkaline compositions for etching copper or alloys thereof

Definitions

• This invention relates to solutions for etching copper in the production of printed wire boards. More particularly, this invention relates to additives for use with an alkaline ammoniacal cupric chloride etching bath which significantly increases the etching rate.
• PWBs Printed wire boards
• Printed wire boards also known as printed circuit boards, are generally manufactured by laminating copper foil onto a non-conductive substrate such as phenolic or epoxy-glass.
• a circuit is made by applying an etch resistant material to the copper foil in a pattern defining the circuit, and then subjecting the P B to the action of an etching solution which dissolves all of the copper not covered by the etch resistant material.
• etching baths may be used.
• the most commonly used etching bath is alkaline ammoniacal cupric chloride, although an alkaline ammoniacal cupric sulfate bath is sometimes used.
• Each of these etching baths has advantages and disadvantages.
• the chloride baths have a higher etch rate than the sulfate baths.
• additives have been developed which can increase the etch rate of the sulfate baths by up to 100%.
• an alkaline ammoniacal copper sulfate etching bath including a mixture of an ammonium halide (preferably 4 - 5 g/L) , a water-soluble salt containing sulfur, selenium or tellurium in the anion (preferably 0.004 - 0.01 g/L), an organic s thio compound containing the group NH_—c—NH— (preferably 0.004 - 0.01 g/L), and, optionally, a water-soluble salt of a noble metal such as silver (preferably 0.004 - 0.01 g/L).
• the sulfate etching bath developed by Cordani et al. has an etch rate almost twice as fast as previously used sulfate baths. Although this is a distinct improvement in the etch rate for the sulfate system, it is still one-half, or less, the rate of an ammoniacal copper chloride bath.
• Chloride etching baths have also been improved by certain additives to increase the etching rate.
• U.S. Patent Number 4,311,551 to Sykes teaches that the addition of cyanamide, or a cyanamide precursor such as thiourea, in amounts of 0.005 - 0.3 g/L, to an alkaline ammoniacal cupric chloride bath increases the etching rate by up to 38%. Given the higher etch rate of the chloride baths over the sulfate baths, this 38% increase is significant and chloride baths containing thiourea are the most commonly used today.
• a conventional aqueous alkaline ammoniacal cupric chloride etching bath may contain the following ingredients: 1.0 - 2.8 Moles/L Cupric ions as metallic copper
• cupric ions are supplied in the etching solution by cupric salts such as cupric chloride, cupric nitrate, cupric acetate, etc.
• cupric salts such as cupric chloride, cupric nitrate, cupric acetate, etc.
• the etching bath is used to dissolve copper, the resulting oxidized metallic copper and reduced cupric ions cause a buildup of cuprous ions (Cu + ) .
• a replenisher solution containing ammonium hydroxide, ammonium salts and/or chelating agents and other ingredients is normally used to control the pH range of the system, to make up for the withdrawn complexing agents for the copper and other ingredients, and to dilute the copper concentration to an optimum level.
• thiourea as an additive in alkaline ammoniacal cupric chloride etchant baths has remained unquestioned in the industry even though the mechanism of the additive is not fully understood. However, it has recently been suggested that thiourea may be carcinogenic. There is therefore a need to find alternative means for increasing the etching rate of alkaline ammoniacal cupric chloride without using thiourea.
• the copper etchant solution additives of the present invention include several compounds, each of which is believed to stabilize the copper(I) state (cuprous ions) .
• the accelerant compounds of the present invention include iodide ions such as potassium iodide, ammonium iodide, sodium iodide, calcium iodide and magnesium iodide and other copper (I) stabilizers such as thiocyanate ions (e.g. ammonium thiocyanate, potassium thiocyanate, sodium thiocyanate, magnesium thiocyanate, and calcium thiocyanate) and thiosulfate ions (e.g.
• ammonium thiosulfate, potassium thiosulfate, sodium thiosulfate, magnesium thiosulfate, and calcium thiosulfate were studied. The results of controlled experiments revealed that adding concentrations up to approximately 600 mg/L of any one of these compounds to the alkaline ammoniacal cupric chloride etchant resulted in a 90- 130% increase in etch rate.
• Figure 1 is a schematic diagram of a prior art PWB etcher and etching process in which the accelerants of the present invention could be used;
• Figure 2 is a graph of the relative etch rate as a function of iodide ion concentration in the etchant
• Figure 3 is a graph of the relative etch rate as a function of thiocyanate ion concentration in the etchant
• Figure 4 is a graph of the relative etch rate as a function of thiosulfate ion concentration in the etchant; and Figure 5 is a comparison graph of the relative etch rate with and without the inventive additive at different temperatures and pressures.
• the prior art PWB etcher 10 which could use the accelerants of the present invention includes a reactor 11 having a spray nozzle 12 and a sump 14.
• a printed circuit board 16 of a standard size is located under the nozzle 12 and subjected to the action of a known concentration of copper ammonium chloride. Replenishers can be introduced into the sump via port 18. The etchant in the sump is recycled to the spray nozzle 12 via line 20 and pump 22. The entire process is monitored by temperature sensor 24 and pressure sensor 26.
• reaction 3b It is believed that the surface oxidation of copper with oxygen in reaction 3b is self-limiting by formation of a protective copper(I) oxide film over the surface of the metal.
• the oxide coating needs to be removed by dissolution for reaction 1 (the reverse disproportionation reaction) to be able to occur.
• the copper(I) stabilizing moiety has particular affinity for the copper(I) oxide and should facilitate its removal.
• compounds believed to stabilize the copper(I) state include iodide ions (e.g. potassium iodide, ammonium iodide, sodium iodide, calcium iodide and magnesium iodide) , thiocyanate ions (e.g. ammonium thiocyanate, potassium thiocyanate, sodium thiocyanate, magnesium thiocyanate, and calcium thiocyanate) , and thiosulfate ions (e.g. ammonium thiosulfate, potassium thiosulfate, sodium thiosulfate, magnesium thiosulfate, and calcium thiosulfate) .
• iodide ions e.g. potassium iodide, ammonium iodide, sodium iodide, calcium iodide and magnesium iodide
• thiocyanate ions e.g. ammonium thiocyanate, potassium
• the preferred embodiment of the invention is the use of a thiosulfate ion accelerant in concentration of 50 to 400 mg/L (400 mg/L preferred) at temperatures up to 50°C.

Landscapes

• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• ing And Chemical Polishing (AREA)
• Preventing Corrosion Or Incrustation Of Metals (AREA)
• Manufacturing Of Printed Circuit Boards (AREA)
• Agricultural Chemicals And Associated Chemicals (AREA)

Priority Applications (10)

Applications Claiming Priority (2)

Publications (1)

Family

ID=22378530

Family Applications (1)

Country Status (18)

Families Citing this family (20)

Citations (7)

Family Cites Families (10)

• 1993
  • 1993-09-08 US US08/118,429 patent/US5431776A/en not_active Expired - Lifetime
• 1994
  • 1994-09-05 MY MYPI94002316A patent/MY111132A/en unknown
  • 1994-09-08 CA CA002168013A patent/CA2168013C/en not_active Expired - Fee Related
  • 1994-09-08 AU AU76830/94A patent/AU676772B2/en not_active Ceased
  • 1994-09-08 IL IL11088594A patent/IL110885A0/xx unknown
  • 1994-09-08 SG SG1996008558A patent/SG50682A1/en unknown
  • 1994-09-08 BR BR9407432A patent/BR9407432A/pt not_active IP Right Cessation
  • 1994-09-08 ES ES94927357T patent/ES2146662T3/es not_active Expired - Lifetime
  • 1994-09-08 DE DE69423904T patent/DE69423904T2/de not_active Expired - Fee Related
  • 1994-09-08 HK HK98105633A patent/HK1006580A1/xx not_active IP Right Cessation
  • 1994-09-08 GB GB9602280A patent/GB2295585B/en not_active Expired - Fee Related
  • 1994-09-08 JP JP7508767A patent/JPH09502483A/ja not_active Ceased
  • 1994-09-08 CN CN94193307A patent/CN1057800C/zh not_active Expired - Fee Related
  • 1994-09-08 DK DK94927357T patent/DK0722512T3/da active
  • 1994-09-08 KR KR1019960701176A patent/KR100330634B1/ko not_active Expired - Fee Related
  • 1994-09-08 WO PCT/US1994/010035 patent/WO1995007372A1/en not_active Ceased
  • 1994-09-08 EP EP94927357A patent/EP0722512B1/en not_active Expired - Lifetime
  • 1994-09-21 TW TW083108662A patent/TW412601B/zh active

Patent Citations (7)

Non-Patent Citations (1)

Also Published As

Similar Documents

Legal Events