Guest Editorial -For Plateworld.com                         

 Don Baudrand, Don Baudrand Consulting,   e-mail:donwb@tscnet.com


Procedure for Electroless Plating High Permeability Metallic Deposit onto Ceramic Substrates

I Preparation of ceramic for electroless plating

  1. The ceramic must be clean, no fingerprints or soils of any kind. The best way to accomplish this is to use an alkaline non-silicated cleaner. There are many proprietary products available from plating chemical suppliers. Alternate, make up a solution of 30 g/L sodium hydroxide 10 g/L sodium carbonate, 10 g/L sodium pyrophosphate and 0.1% surfactant (Triton x-100, or many other choices) Heat to 75C . Immerse the ceramic for about 2-3 minutes, rinse and proceed with the preparation.
  2. Acid treat using 20% by vol. hydrofluoric acid for about1 minute. This step may vary with the type of ceramic.
  3. Rinse using DI water
  4. Catalyze the surface as follows. A. Use stannous chloride solution for 1-2 minutes. The solution is made as follows: 10 g/L stannous chloride and 20 ml/L hydrochloric acid.
  5. Rinse
  6. Immerse in a solution of palladium chloride for 2-3 minutes. 1g/L palladium chloride and 10 ml/L hydrochloric acid.
  7. Rinse
  8. Hydrochloric acid dip 5% by vol. 20-30 seconds
  9. Rinse
  10. Electroless plate to desired thickness. About 1 hour will deposit 0.0002" (5 uM)

II Electroless plating solution

Formula: Add ingredients in the following order:

Two Liter plating solution

Sodium citrate 28 g/L 56 Grams

Sodium glycolate 10 g/L 20 "

Ammonium sulfate 34 g/L 68 "

Erythorbic acid 5g/L 10 "

Nickel sulfate.6H2O 13 g/L 25 "

Ferrous sulfate.7H2O 20 g/L 40 "

Dimethyl amine borane 3 g/L 6 g/L

Adjust pH to 9.2 (+-1) Using a sodium hydroxide solution. 40 g/L, add very slowly with constant stirring

Operating temperature 70C

Comments: Citric acid must be synthetic grade. (Do not use fermentation grade.) Available from many chemical supply houses.

Sodium glycolate must be pure, use analytical grade, Available from lab chemical suppliers. Ferrous sulfate and ammonium sulfate should be AR grade also.

Dimethyl amine borane (DMAB) is available form Bayer (Germany) through US chemical suppliers. Bayer supplies a pure form. Others are not satisfactory. Callery Chemical supplied DMAB of good quality, but I believe they no long produce it.

Erythorbic acid is iso ascorbic acid (vitamin C is ascorbic acid) Eyrthorbic acid is much less expensive than vitamin C and equally effective for deoxidizing. ( but 1/20 as effective if used as the vitamin)

Alternate for the catalyzing steps:

Proprietary materials are available from plating suppliers such as MacDermid, Shipley -(Rhome and Haas) Enthone and others. The steps are as follows: 1. Dilute hydrochloric acid dip, rinse, catalyze using the proprietary produce (contains palladium/tin colloidal suspension). Rinse, Accelerator dip, (proprietary) Rinse then electroless plate.

Maintaining the plating solution:

Adjust pH using dilute sodium hydroxide or ammonium hydroxide. I prefer ammonium hydroxide, but it is unpleasant and it takes a fair amount to raise the pH. Sodium hydroxide works well but it must be added very slowly with constant stirring from a dilute solution of NaOH.

Nickel, Iron and DMAB will be consumed during plating.

It is best to analyze the nickel content and add DMAB and Iron in proportion to the nickel needed during plating. Analyze the solution for nickel and iron after plating cycle to make fine adjustments. For each gram of nickel as metal add 1.5 grams of DMAB (dimethyl amine borane). Nickel sulfate.6H2O contains 22.3% nickel. Additions should be made every 15 to 30 minutes of plating time. Temperature should be constant +- 2 degrees if possible. Plating rate and composition of the alloy change with temperature to some degree. High temperature will decompose the DMAB ( the most expensive ingredient) at a faster rate than the 1.5:1 ratio. The theoretical ratio is 1:1 DMAB to I Nickel, but at 70C more DMAB is consumed.

Erythorbic acid will be consumed also. It is there to prevent oxidation (rusting) of iron that is exposed to the air at the solution surface. Add about 1g/L ( 2 grams in the plating solution) after each run.

If corrosion resistance improvement is necessary, the addition of cobalt can be made to the plating solution. This addition will require adjustments in all other ingredients, and the addition of another organic (Glylcine) to the formula.

An alternate formula using sodium hypophosphite can be worked out. However, the literature indicates lower Oersteads (Oe) using Boron i.e. dimethyl amine borane. There are also formulas using sodium borohydride. However, these solutions tend to be very unstable and must operate at pH 12 or higher, I do not recommend this formula.

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