EN Process Performance: Effect of Agitation, Loading and Stabilizer Level

EN Process Performance:Effect of Agitation, Loading

and Stabilizer Level

By Matthew J. Sisti and Jean LaPlante

Presentation Outline

Brief introduction and process reviewExperimental objectivesExperimental proceduresResultsConclusions/Recommendations

Brief Introduction & Process Review

Early formulations had many shortcomings

Turbidity, instability, short solution life as well as poor deposit characteristics were commonplace

Commercial success of EN led to technological advancements

Brief Introduction & Process Review (cont.)

Contemporary EN formulations: are easy to make up and operate.are typically consistent from lot to lot.offer many process and deposit benefitsare available in “all shapes and sizes”still suffer from a number of technical

flaws!

Periodic problems with current EN technology (the 6 P’s)

Poor corrosion resistance due to high deposit porosity.

Inferior deposit passivity resulting in poor chemical resistance and staining.

Pitting of thick depositsEdge pullback and related phenomenaSlow plating ratesModerate to high plate-out

Balance

EN is a process in a perpetual state of conflict

High purity solution yields highest quality deposit.

Impractical in terms of process performance:Not User-Friendly

Must find balance between optimum deposit and process performance.


Brief introduction and process reviewExperimental objectivesExperimental ProceduresResultsConclusions/Recommendations

Experimental Objectives

deposit porosity deposit passivity pitting edge pullback slow plating rates plate-out

Can we modify an EN process to maximize performance?

Deposit porosity

EN is cathodic to the substrate in more than 75% of current applications.

Corrosion of the anode (substrate) occurs through deposit porosity.

Porosity can be reduced through pretreatment and EN chemistry.

Current study will evaluate porosity reduction through modified solution operation.

Deposit passivityPassivity relates to a more “impervious”

condition of a particular metal or alloy.Indirect measurement of deposit purity and

phosphorus content.Co-deposition of impurities reduces passivity.RCA nitric acid test was used to compare

“passivity” of deposits plated under different conditions.

Deposit pitting

Thicker deposits (>1.0 mil) are more susceptible.

Medium phosphorus processes produce more pitting.HPEN has 1/4 of HM stabilizerHPEN plates 1/2 speed

Deposit pitting of a HPEN process under various conditions were evaluated.

Edge pullbackTypically caused by high concentrations of

HM stabilizers, brighteners and/or metallic contaminants.

Co-deposition is governed by diffusionHigher concentrations of stabilizers adsorb in

areas of high solution velocity (i.e edges)

Effect of loading, agitation and stabilizer level on edge effect phenomena will be evaluated.

Plating rateCritical process characteristicFunction of:

TemperaturepHSolution ageChemistry type, exaltants, hypophosphite level

Our study focused on the effect of :Stabilizer type and levelAgitationWorkload to solution volume

on plating rate

Plate out/solution stabilityMany factors play a role in process

stabilitySolution chemistryOperating parameters (pH, Temp., Conc.)Equipment and maintenance

Our study focused on the effect of :Stabilizer type and levelAgitationWorkload to solution volume

on solution stability



Experimental Procedures

Pertinent data can be found in the Conference Proceedings

Critical notesAll solutions tested were high phosphorusAll EN solutions were aged to 0.5 mto’sSubstrates were 1010 mild steel panels

and 1”x 1/4” sheet metal screws.

Experimental Procedures (cont.)

TestingPorosity

Ferroxyl per ASTM B733 of 1” bolts plated to 0.4 mils.

PittingPanels plated to 2.0 mils and examined at 20x.

PassivityPanels plated to 0.2 mils, dried and immersed in

concentrated nitric acid.Time to black edges as well as entire panel.

Experimental Procedures (cont.)

TestingPlate-out/instability

Palladium stability Evidence of plate-out

Cleaning cycleConventional cycle for low carbon steel

with two electrocleaning and acid activation steps.

Test Standardization Solution pH: 4.8 Temperature (F): 190 Agitation: moderate Loading: 0.4 ft2/gal Stabilizer level (ppm): varied

Heavy metalstabilizer(ppm)

Pitting panel(# of pits)

Ferroxyl results(# of blue spots)

0.3 4 140.3 3 80.3 5 90.3 3 100.1 0 00.1 0 00.1 0 00.1 0 0



Effect of Solution AgeMTO Ni

(g/l)Hypo(g/l)

Ortho(g/l)

Spec.Gravity(g/cc)

PlatingRate(mph)

HMppm

Passivity(min)

Pores Pits PlateOut

0 6.0 30.0 2.0 1.052 0.55 .35 8 4 11 No

1 6.0 29.4 41 1.080 0.52 .37 n.a 7 8 No

2 5.9 30.3 61.7 1.094 0.48 .31 n.a 5 15 Lt

3 6.1 30.3 85.1 1.118 0.46 .38 n.a 15 5 No

4 5.7 29.4 124.4 1.141 0.42 .41 n.a 12 5 Lt

5 5.8 31.5 157.5 1.168 0.40 .44 n.a 22 8 Lt

Effect of Stabilizer Level Solution pH: 4.8 Temperature (F): 190 Agitation: moderate Loading: 0.4 ft2/gal Stabilizer level (ppm) variable

HM StabilizerLevel (ppm)

Pores Pits Passivity(minutes)

Platingrate

(mils/hr)

Pullback Plate-out(mls Pd)

0.1 0 0 1/8 .51 No 6 mls0.3 13 4 1/8 .54 No 12 mls0.6 20 21 .75/5 .47 Yes 16 mls1.0 25 24 .33/4 .47 Yes 26 mls

Ferroxyl Porosity Test for

0.4 mil HPEN - 0.1 ppm HM Stabilizer

Ferroxyl Porosity Test for

0.4 mil HPEN - 1.0 ppm HM Stabilizer

Porosity of 0.4 mil HPEN deposit vs

Heavy Metal Stabilizer Level

0.1 ppm 0.3 ppm 0.6 ppm 1.0 ppm

Effect of Solution Loading Solution pH: 4.8 Temperature (F): 190 Agitation: moderate Loading: variable Stabilizer level (ppm) 0.3

Solutionloading(ft2/gal)

Pores Pits Passivity(minutes)

Plating rate(mils/hr)

Pullback Plate-out (mls Pd)

0.05 36 39 10 sec/2 .54 Yes n.a.0.10 20 15 40 sec/3 .46 No n.a.0.40 13 4 1/8 .54 No n.a.1.0 36 5 2/8 .56 N0 n.a

Effect of Agitation Solution pH: 4.8 Temperature (F): 190 Agitation: variable Loading: 0.4 ft2/gal Stabilizer level (ppm) 0.3

Agitation Pores Pits Passivity(minutes)

Platingrate

(mils/hr)

Pullback Plate-out(mls Pd)

Moderatestir bar

13 4 2 / 8 .54 no 12 mls

Noagitation

6 8 10/15 .52 no 8 mls

Excessive 16 2 1 / 5 .60 no 10 mlsModerate

air16 2 1 /10 .61 no 22 mls

Moderatenitrogen

15 2 2 / 10 .53 no 22 mls

Results (cont.)- Synergy

Results thus far are for experiments with only one operating parameter varied.

Real world operation of an EN process is not so static.

Optimized performance requires combination of ideal conditions.

SynergyThe final group of 120+ experiments

were run holding one parameter constant while all others were varied.

The results were tabulated, sorted and trends recorded.

Analysis of Synergy Data

Due to volume of data, averages of testing results were utilized.

Simplified analysis procedure and eased trend recognition.

Sorted porosity and pitting data can be found in the proceedings.

HM Stabilizer level vs Deposit Porosity and Pitting

0

20

40

60

80

100

120

140

# o

f p

its/

po

res

0.1 0.3 0.6 1

Heavy metal stabilizer (ppm)

pits

pores

Solution Loading vs Deposit Porosity and Pitting

0102030405060708090

100

# o

f p

its/

po

res

0.05 0.1 0.4 1

Solution loading (sq. ft./gal)

pits

pores

Agitation vs Deposit Porosity and Pitting

0

20

40

60

80

100

120

# of

pits

/por

es

moderate

excessive

airnitrogen

Solution loading (sq. ft./gal)

pits

pores



Conclusions

Effect of solution age:Deposit porosity increases

Deposit pitting appeared unrelated (to 5 mto)

Effect of heavy metal stabilizer:Higher levels promote porosity and pitting

Plating rate independent

Higher levels reduced passivity

Higher levels increased stability

More pronounced edge effect phenomena

ConclusionsEffect of workload to solution volume:

Higher loading reduced deposit pitting and increased deposit passivity.

Plating rate was independent of loading.

Effect of solution agitation:Pitting reduced with moderate air/nitrogen.High rotational agitation increased pitting and reduced passivityDeposit porosity increased with agitationHigh rotational or air agitation increased speedSolution stability increased with agitationNo benefits from nitrogen were realized

Suggestions

Pay close attention to solution loading.

Underloaded solutions should be run below 85% activity and agitation reduced. Monitor stability.

For heavy build applications-run at 85% activity or below and utilize air agitation.

Suggestions

To increase stabilityMaintain chemistry at or near 100%Increase solution movement (add air)

To eliminate edge effect phenomenaMaintain chemistry at or below 85%Reduce agitationIncrease workload Monitor concentrate age

Suggestions

To improve corrosion protectionMaintain chemistry at or below 85%Reduce agitation

To increase passivityMaintain chemistry at or below 85%Increase workloadMaintain plating speed below 0.5 mils/hr

Finally..........

Work with your supplier.Ask for type or class of

stabilizer and target level Ask about designer EN

Key to success is balance between deposit and process performance

Documents

EN Process Performance: Effect of Agitation, Loading and Stabilizer Level