In order to maintain an EN solution a thorough understanding of its chemical and physical process variables is extremely important, as these govern the final deposit quality and properties.
Troubleshooting of EN baths may be grouped into: a) deposit problems such as poor adhesion, blistering, roughness, pitting, dull deposits, streaky deposits; or b) bath issues such as no plating, slow or fast plating rates, bath decomposition, solution turbidity. After identification of root cause of a given defect, proper measures should be adopted for remediation.
Problem: EN film exhibits blisters, tends to peel
Probable cause/solution: a) poor surface preparation; b) inadequate activation; or c) surface contaminations with embedded soils, organics, oils, etc.
Problem: EN bath manifests low plating rates
Probable cause/solution: a) low nickel concentration which may be ascertained by EDTA titration; b) low hypophosphite concentration determined by iodometric titrations; c) low pH which may be adjusted by using NH4OH or K2CO3; d) low temperature of the bath – corrected by adequate heating and improved agitation; e) higher concentration of stabilizer (follow directions from the bath supplier. This may make bath critical resulting in plate-out. A new bath preparation bath may be justifiable); f) apply optimum load ratio; g) bath is old and out of balance; or h) bath overheated without work.
Problem: The plating rate is too fast
Probable cause/solution: a) check solution chemistry; b) use 5µ, 1µ filters in succession to avoid excessive particles in the bath; c) high temperature; or d) pH is too high, which may render the bath critical and spontaneous plate-out.
Problem: The bath consumes too much nickel
Probable cause/solution: a) high drag-out, which can be eliminated by replacing stagnant rinses; b) bath may become critical and lead to sudden decomposition. (This can be remedied by adequate filtration); and c) high loading factor – decrease workload.
Problem: EN plating solution is murky and cloudy
Probable cause/solution: a) pH too high; add H2SO4 to lower pH; b) excessive drag-out losses; or c) complexing agents may be low, which can be replenished by addition of make-up additive.
Problem: Rapid changes in bath pH observed
Probable cause/solution: a) excessive drag-in of pretreatment chemicals, which can be improved by efficient rinsing; b) loading factor high; decrease work load; or c) improve buffering action to control pH.
Problem: Workload exhibits patchy step plating or skip plating
Probable cause/solution: a) metallic contamination; b) the substrate effect due to lead content; the skip plating can be corrected using a copper or nickel strike; c) over-stabilized bath (do dummy plate or dilute the bath); or d) incorrect pH.
Problem: No deposition on the work is observed
Probable cause/solution: a) solution is out of balance; b) contamination by foreign materials; c) pH too high; d) bath is excessively heated; e) over-stabilized bath- dilute bath; or f) low pH and temperature.
Problem: Plated parts are rough
Probable cause/solution: a) faulty surface preparation; b) drag of suspended solids; c) improper cleaning and rinses; d) pH too high; e) inadequate Ni chelation; or f) contamination from multiple sources such as water, rinses, oils, dirty filters, liners and airborne shop dust.
Problem: Non-uniform or skip plating on the parts
Probable cause/solution: a) imbalance in stabilizers or accelerators; b) rust on parts; improper pretreatment; or c) excessive stabilizer levels, which can cause pull back or no plate on edges. All these problems can be corrected by maintaining chemistry in optimal ranges and adequate pretreatment. Imbalance in chemistry is also the root cause of variability in appearance of parts being too dull or too bright. A well-established bath yields good parts. Stains on parts can be prevented with good rinses and adequate drying.
Problem: Flaking of plating film observed at random?
Probable cause/solution: Peeling or flaking is usually due to improper cleaning or activation of substrates. The importance of pretreatment cannot be overemphasized. Matching the proper cleaning and activation processes for the type of metal and the manufacturing method are the prerequisites to having a robust process to handle variations in soils and oils left on the part.
Problem: Why there are stains on parts?
Probable cause/solution: a) inadequate rinsing; b) parts not dry; or c) improper packing (pack with desiccant or under nitrogen).
Problem: The parts are pitted
Probable cause/solution: a) suspended solids in the bath; b) loading ratio too high; c) organic and metallic contamination; or d) poor hydrodynamics in the bath.
Problem: The parts are dull and cosmetically dark
Probable cause/solution: a) old bath; b) presence of organic and inorganic contaminants; c) low nickel and hypo; d) low temperature; e) low pH; f) inadequate surface preparation; or g) contaminated rinses.
Problem: The plating is streaky or patterned
Probable cause/solution: a ) poor agitation; b) poor surface preparation; c) metallic contamination; d) residues on surface; or e) gas pattern due to reactions.
Problem: The bath is unstable
Probable cause/solution: a) high temperature; b) high pH; c) local overheating; d) plating tank not passivated properly; e) airborne particles; or f) large additions to bath.
A thorough understanding of EN chemistry is a prerequisite to the evaluation of solution stability and purity, which have a direct impact on plating speed, product quality, and waste generation. Improper chemical balance and excess contaminants will hasten spontaneous decomposition of the bath or decrease the plating rate or quality below acceptable levels.
There are no short-cuts for achieving a reliable EN process. A decent quality product can only be obtained if the diligent efforts are made to robust solution control, eradication of organic and metallic impurities, implement clean rinses, periodic preventive maintenance of the line, keeping accurate records of additions, total area of processed parts, details of various metal substrates processed and impartial audits.
ABOUT THE AUTHOR
Sudarshan Lal, Ph.D. CEF, and industry consultant, specializes in electroplating, bath development and optimization, installation, monitoring and process control. He has extensive research and development experience as well as and hands-on evaluative experience in precious plating, alloy plating, electroless and electrolytic reel-to-reel plating. Dr. Lal holds seven U.S. patents and has contributed to scores of electrochemistry-related research publications. You may contact Dr. Lal at (717) 732-5899 or via e-mail: firstname.lastname@example.org