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Addition Agents in Electroplating Processes

Dr. R. J. Patolia SHREE HARI GROUP OF INDUSTRIES

5/9/2020

Electroplating is a science as well as arts also. We know that formulated ready to use proprietary chemicals are available in market for all short of purpose and application.

Idea of this review to you all, is to teach you well, understand the subject well, act effectively, save time, money, rejection and to achieve good quality work.

Now we will discuss the function, application and use of various Addition Agents. They are added in controlled quantities in electroplating baths to get required properties of the electro deposited metals or articles. They also differ from process to process. Their use and consumption depend on the quality and properties of the electrolyte such as chemical nature, pH, temperature, cathode polarization power and electro-deposition potential of the metals. In short we define these Addition Agents as

ADDITIVES / CARRIERS :
  • They are absorbed on cathode surfaces during plating process to form a monolayer film and works as a barrier to diffusion of metal ions to cathode surface and there by control the plating rate to get fine uniform deposition.

LEVELLERS :
  • They are absorbed strongly on cathode surface at the high current density region thus lowering the plating rate at peaks by polarization and simultaneously increase the plating rate at valleys due to low polarization.

BRIGHTENERS :
  • They get attached to the metal ions in electrolyte and make the deposition process easier, control grain structure and increase brightness, hardness and other properties of the deposit.

WETTERS :
  • They lowers the surface tension of the Electrolyte at cathode surface and release the gas molecules from the cathode surface to reduce the tress and hydrogen embrittlement of the deposit.
  • The wetting agents required are comparatively very high in case of acidic bath – such as Acid Zinc, Acid Tin and Acid Copper baths, while the brightening agents are very less because only a mild polarization is required to get levelled and bright electro deposits.

PURIFIERS :
  • To improve colour, brightness of the deposition at low current density area, specific metal chelating agents are used as a purifier to control or stop diffusion of unwanted trace metals. Eg., Cu in Ni. Cu, Pb, As in Zn.
  • Now we discuss some plating processes with respect to different addition agents used during electro deposition of metals.

HEXAVALENT CHROME PLATING :
  • Highly acidic and strong oxidizing nature of the bath react as, if you add any organic substance, it gets oxidized and lost totally. For brightness, fine grainment only Sulphuric Acid, Fluorosilicic Acid (H2SiF6 ) or Methane Sulfonic Acid are used for getting uniform, hard, bright deposits, plating efficiency is only 12 to 27% maximum, while rest current will utilized for hydrolysis of water to generate Hydrogen at cathodes and Oxigen at anodes surfaces. Accumulation of Hydrogen may leads to explosion. For fumes or mist suppressants Perfluoro Sulfonate are used.

ACID COPPER BATH :
  • Highly Acidic Bath, having free Sulphuric Acid from 50 - 110 gm/liter. Only high molecular weight polyethylene Glycol (PEG) from 6000-20000 grade are used as a carrier and stable simple Thiosulfonic Acid derivatives such as SPS, DPS, ZPS, MPS etc. are used as a brightener.

ACID TIN BATH :
  • Acidic bath, where short chain Non-Polar wetting agents such as Octylpenol, Nonyl Phenol EO condensate are used. Cresols, Napthols Sulfonic Acid are used as a carrier. OCB, BAR are used as a Brightener.

ACID ZINC BATH :
  • As a wetting Agents OP, NP or Beta Naphthol EO-20 Condensate are used. SB, DEG, IPA, TEMMOL (Phenol-Formaldehyde condensates) are used as a carrier OCB or BAR are used as a Brighteners.

ACID GOLD PLATING :
  • Polyhydroxy organic Acid or Phosphoric Acid are used as a Metal  complex formation, to slowdown the plating process. Methane Sulfonic Acid or Puridine-3-Sulfonic Acid are also used as a complexing agents to make process very slow and it result into fine grainment. For increasing the hardness of the deposit, cobalt, Nickle or Indium Complexes are used in required proportion. For more brightness of the deposit amines such as Diethlene Triamine (DETA), TETA, TEPA are used.

NICKEL PLATING :
  • This is stable, near to neutral bath of working pH 3.8 – 5.2. Nickel Sulfamates, Nickel Sulphates, Nickel Chlorides and Boric Acid are used for bath preparation. Wetting Agents like sodium Lauryl Sulphate and or Sodium 2-Ethylhexyl Sulphate are used in very less concentration of 2-5 mg/liter of bath. The chemistry of Nickel plating process is totally different from the other processed and it is used 65 to 75% as compare to all other processes.
  • Unsaturated reactive organic derivatives with double or triple bond and or their sulphonate or mono-bis ethylene /propylene oxide condensates and Betaines containing positive and negative charged molecules are used as a brighteners.
 
TABLE
Function, application and use of various Additives / carriers, Levellers, Brighteners wetters, Purifiers etc. in semi bright, Bright, Tri, Heavy and Satin Nickel plating processes.
No. Chemicals Bath Brightness Ductility LCD Area Micro Throwing Power gm / litre Remarks & Application
1 Coumarin G UDB Average Clear Good - Not Commercialized.
2 OTSA G DB Average Clear - - Used in Early time, Found Not so useful.
3 PTSA G DB Average Clear - - Used in Early time, Found Not so useful.
4 Saccharin B,T,S UDB Good Clear Good 0.900 Versatile, Highly Stable, Not Consumed in Electrolysis.
5 BBI B,T,S UDB Good Clear Good 0.125 Stable, Low cost in use, Effective at less concentration. Clear deposit up to far of LCD.
6 SVS B,T,S UDB Good Clear Good 1.500 Not used due to less availability.
7 SAS B,T,S UDB Good Clear Good 2.500 Versatile, Highly stable and used in maximum application.
8 NTSAG H DB Good Clear Good 2.000 Used in Electroforming for Heavy Deposit.
9 Salieylic Acid SB UDB Very Good Clear Good 1.500 In Sulfer free semibright bath. Stable and Less consumed
10 SPS S,T,S UB Good Clear Better 0.020 Very good leveller, used for thin deposited decorative parts.
11 DMP B, T, S UB Good Clear Better - Not commercialized, due to less unavailable in market.
12 DEP B, T, S UB Good Clear Better 0.005 Used for thin deposited decorative parts, very good leveller. Can we used at higher concentration.
13 BD SB,B,S UB Moderate Skip Good 0.040 Highly active strong molecules, used in decorative and SB process at minimum concentration
14 HD SB UB Moderate Skip Good 0.100 For Semi bright process.
15 PHD SB UB Good Clear Good 0.080 Versatile for SB Process.
16 BEO B,T,S UB Moderate Skip Good 0.080 Versatile for Decorative Parts.
17 BMP B,T,S UB Moderate Skip Good 0.025 For Decorative, Quick result
18 PAP B,T UB Moderate Skip Good 0.018 For decorative Formulations
19 PME B,T UB Moderate Skip Good 0.015 For decorative Formulations
20 PPS B,T EB Moderate Skip Good 0.025 Very useful for bright and decorative formulations, but costly
21 PPSOH B,T EB Moderate Skip Better 0.035 Very useful, cost effective in decorative formulations
22 MPPS B,T EB Moderate Skip Better - Useful, but high cost.
23 MPPSOH B,T EB Moderate Skip Good - Useful, but high cost.
24 SBS SB,B,T Dull Everage Best Coverage Better 0.015 Purifier for Cu, Fe etc.
25 SPTS SB,B,T Dull Everage Best Coverage Better 0.020 Purifier for Cu, Fe, Cd etc.
26 ATPN SB,B,T Dull Everage Best Coverage Better 0.006 Purifier for Heavy Metals -Cu, Pb, As, Sb.
27 SDTC SB,B,T - - - - 0.001 Purifier to remove heavy metals Cu, Pb, As, Sb, Fe etc. as insoluble form in filter pack.
28 SEHS SB,B,T - - - - 0.005 Wetter to reduce surface tension, Pitting in high current density area.
29 SLS SB,B,T - - - - 0.000 Wetter to reduce surface tension, Pitting in high current density area.
30 Carbon SB,B,T - - - - 0.250 To remove unwanted organic through filtration.
 

 

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