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The Lost Art of Tin-Nickel Plating:
Compare the podcasts to published literature
 
by Tom Pullizzi, CEF, Secretary, finishing.com, inc.
Podcasts and webpage copyright 2011 by finishing.com, inc.


Methods

A tape titled "The Lost Art of Tin Nickel Plating" by L. Morin, dated 1990 was received by finishing.com, inc. from the author, Lou Morin in 2001. Notes were taken on the contents of the tape for the purpose of a study of this electroplating process. It is hoped that the information in this study, along with publication of podcasts of portions of the audio tape, will be useful to professional metal finishers who wish to add this alloy to their repertoire.

The author wishes to thank Wes Mingin, musician, teacher, and all-around nice guy, for converting the cassette tape to a digital file, and for his advice on all things to do with audio.

The information presented in the Morin tape, in the opinion of this writer, does indeed show differences between the experiences of Mr. Morin and the data presented in the literature. The reader should listen to the tapes and make their own judgement on how to use the information for their own use. Mr. Morin describes a simple control of his tin nickel formulation with only tin and nickel analysis, Hull Cell control of grain refiner, and one additive control for pH adjustment.


References

Lou Morin, 1990, audio tape "The Lost Art of Tin-Nickel Plating" finishing.com library, Brick, NJ

Electroplating, J.B. Mohler, Chemical Publishing Co., New York, 1969

Metal Finishing Guidebook and Directory (MFGD), 2002 Guidebook and Directory, Tin-Nickel Alloy Plating, S.K. Jolata,

Ibid, Test Methods of Electroplating Solutions


Warranty and Disclaimer

finishing.com gives no warranty, express or implied, on the accuracy of any information contained in this informational bulletin. The chemicals and procedures described in this document are hazardous and users of this information must verify any and all of it before using or testing in their own facility. The information is for review and use only by professionals trained and experienced in the art and science of commercial electroplating. The hazards associated with tin-nickel alloy electroplating require special techniques, experience, plant, and chemicals which need special treatment. The environmental, waste treatment, safety engineering, and plating of this alloy to commercial applications can only be done successfully in a quality controlled electroplating plant by experienced chemists and engineers.

No part of this bulletin should be considered complete as a guide to successful tin nickel alloy plating. The information is only a starting guide for those who wish to embark upon a process of learning, understanding, and research into the safe and efficient use of nickel alloy plating.

No chemical or device described in this informational bulletin should ever be purchased, stored, or used except in the confines of a secure commercial facility designed to prevent misuse or misappropriation by anyone in the general public.

by Tom Pullizzi, CEF, email pullizzi@verizon.net


Notes:


Potential uses/Special properties of Tin Nickel electroplate

  1. high productivity, high racking density
  2. improve tap life when used with wax as coating for brass to be subsequently drilled and tapped
  3. nickel/tin nickel substitute for nickel/chrome on wire racks
  4. 1/3 to 5 micron coating thickness on copper and copper based alloys
  5. super flat plating across current density
  6. polishes to optical figures
  7. tops to batteries containing Hg, KOH electrolyte at a slight positive pressure in the can
  8. Tin nickel forms an amalgam with Hg
  9. mechanical watch, brass barrel gears, gyroscope movements, components
  10. high gear tooth loading and pivot points
  11. ability to bond to lubricants
  12. extreme throwing and covering power into deep recesses
  13. plating at extreme high current densities (tips and projections)
  14. alloy of the deposit unaffected by cathode current density in plating range
  15. self regulated lubrication of deposit at pressure points
  16. activate Monel and stainless steel by 1 minute immersion in the tin-nickel plating solution (substitute for Wood nickel strike)
  17. barrel plate the inside of small diameter tubes (substitute for electroless chemical deposition)
  18. high compressive stress of coating limits elongation limits post plating dimpling or staking
  19. heat cup in the bottom of percolators
  20. compatible for food use and possibly medical uses
  21. corrosion resistant to chemically aggresive inks
  22. resistant to nitric bright dips
  23. resistant to caustic solutions
  24. pump parts
  25. ignition point sets
  26. mainspring components
  27. salt water hardware
  28. close tolerances
  29. polar attraction to organic acids/lubricants
  30. throwing power to plate the inside of deep recesses (e.g., ball point pen cartridges) without internal anodes
  31. equal to Ni/Co alloy gold in contact resistance
  32. base for thin coating of gold
  33. solderability better than straight nickel
  34. plating of valve components that will be fouled by salts of evaporation
  35. 0.003 inches plated on cast steel for extreme corrosion resistance for caustic solutions*
    *compressive stress makes this coating extremely brittle
  36. low contact resistance. Used in IBM (nickel iron wire card readers) punch card readers, paddles in reed relay electrical contacts. 0.01 diameter wire sealed in glass tube with tiny gap gold and rhodium. 400 milliwatt contact held together with a magnet from outside the evacuated device
  37. Non-magnetic
  38. high cavitation resistance, low coefficient of friction with water (e.g., racing boat propellers, bronze and carbon steel)
  39. fishing chairs coated with tin nickel, untouched by salt water after two years, requires only rinse with fresh water
  40. a coating sacrifical to copper based alloys that does not form a voluminous corrosion product
  41. hand tools, e.g. vise grip pliers, bright nickel, tin nickel, water soluble wax, plate 8 minutes nickel, 1 minute in tin nickel, water soluble wax
  42. twin brass eyelets, drilled and tapped after plating, on connector boards, 1 micron tin-nickel, water dip wax, very thin, would take forming, bending, phenomenal tap life because of the wax held by the tin nickel
  43. ways and guides for transporting parts, for example to and from an electroless nickel plated vibratory bowl, does not discolor tin plated parts
  44. boat hardware
  45. parts for water meters
  46. deep solder cups with corrosion resistance
  47. anode connections for submerged fluoborate plating solution for continuous coil, wire plating machines
  48. intermetallic compound
  49. promote the use of tin, and copper-based alloys by interested parties
  50. diffusion barrier for copper prior to tin/lead plating
  51. garment fasteners
  52. etch resist for printed circuit boards

Historical Information:

Developed in the 1950's. Dr. Parkinson, inventor, at Tin Research Institute in Middlesex, England


Cautions for specifying tin-nickel coatings


Operating Parameters

Recycling of Rinses, Dragout - Do not recycle because of precipitated tin

No agitation required, keep aeration to absolute minimum to reduce formation of stannic tin.

temperature: 150 minimum - 154 degrees Farenheit

material of construction of tank and plant - highly corrosive solution, contact vendors of plating plant.

anodes - rolled, depolarized nickel anodes and tin anodes (double bag tin anodes), tin chloride added to make up tin.

filters and bagging of anodes - Orlon

filters, plastic or stainless steel


Buffing

Definition of "fanning/color buffing", which is performed on a buffing wheel as described in L. Morin's tape.

Use lime on an open weave buffing wheel, removes tin, polishes the surface and enhances the pink color of the deposit.

fingerprints easily because of attraction to organics, use cotton gloves.


Analysis of nickel and tin

Analysis is by simple titration. Both Langford and Parker and the Metal Finishing Guidebook show the same procedures. Control of other additives is by pH and Hull Cell analysis.


Control parameters of the solution

current density: 25 ASF maximum

nickel chloride 40 ounces per gallon (opg)

ammonium biflouride makeup 7.5 opg

tin chloride 6.5 opg

Keep within 90 to 100 percent of this cencentration by analysis. and nickel and tin chloride for maintenance

Grain refiner control: sodium fluoride is 2 opg as makeup, Daily Hull Cell test.

Hoeing up: stratification of solution - hoe up the solution 2/3 down up and down 1/2 dozen times, heavy stuff will settle and no more hoeing is required for the rest of the shift. In a half hour, all solids will settle and the tank should run the rest of the day.

ammonium biflouride makeup: 7.5 opg. Control during use by use of pH Hydrion pH paper. 2.5 - 2.8 pH, low add ammonium hydroxide, if high add ammonium bifluoride.

Carbon treatment and dummying are not necessary. It is important to keep oils and other organics out of the plating tank by use of previous cleaning and rinsing steps.

Solution Maintenance: keep at 90 to 100% of makeup for nickel and tin, control pH to within NaF is the brightener and grain refiner. Hull Cell test, 1 amp, 10 minutes, 150F. should be bright to 25 ASF. Burn free to 40 ASF.

stannic tin removed by pumping solution at 150F to a treatment tank, filter back into cleaned plating tank at 100 F using a 10 micron filter.

Rack plating - 0.5 to 1.5 volts, do not need cathode rod agitation.

Shelf roughness caused by stannic tin, see hoeing up porcedure.

keep barrel well submerged to prevent aerating the solution

Post plating steps: after plating, 10% ambient temperature HCl, 30 seconds or less, the white cloud is the stannic tin (if you dehydrate the salt, you will need boiling HCl to remove it), follow by rinse, rinse in water.

Wise to use a gold chloride strike before gold

cyanide gold cathodic 4.5 V 30 sec

acid gold without gold chloride strike, go direct at HCD, 7 millionths of an inch, only needed for solderability, shelf life, moving line contact, more lubricous than indium alloy gold would be. PCB connector tabs.

More information about plating teapots, with the handles and spouts. If you have copper based alloy part with this kind of high and low current density areas, think about tin-nickel plating to forget about shields, robbers, internal or special anodes.

Reactivation of nickel: immersion in the tin-nickel solution without current.

fingerprints don't show as much on a curved surface.


Special Procedure for making anode connections for submerged fluoborate plating solution where anodes are submerged in a fluoborate plating solution (listen to podcast for L. Morin's description)

drill and tap copper terminal 1 inch square stock, one half 3/8-16 turned screw on one side. the other half a socket hole. Tin nickel this piece to 5 microns thickness.

vinyl insulated welding cable, trim the line cleanly. solder dip the end of the wire and solder into throat of the tin nickel plated brass piece.

Use rack coating touchup masking to cover solder area, use to terminate in fluoborate coating solutions under the solution. This connection should last for the life of the anode.


Just a few questions that have been answered in Lou Morin's excellent discourse about tin-nickel plating from the chloride-fluoride bath:

Why would you put a copper strike under the tin nickel plate?

Why would you put a tin nickel deposit in boiling concentrated phosphoric acid?

What is the main problem with plating thick deposits of tin-nickel?

What was the application of tin-nickel in electric percolators?

How did Mr. Morin demonstrate the amazing throwing power of this solution to customers?

What are the two functions of sodium fluoride in tin nickel plating?

How do you control the grain refiner in the bath?

What voltages would you expect in barrrel and rack plating?

What are the materials of choice for heating coils?

How do you maintain the anodes?

How do you maintain the bath for stannic tin?

How corrosion resistant is this deposit; several surprising examples

These and many more are discussed in the podcasts, don't miss them!

 

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