www.metalfinishing.com May 2012 I metalfinishing I 39

High-Build, High-PhosphorusElectroless Nickel Plating

Process achieves plating to 20mils—without pitting.

I ntroduction. Over the past year,Ronatec has been developing new

and innovative products that allowelectroless nickel (EN) users toachieve high-build thicknesses oversteel and aluminum substrates,with some customers reachingbuilds of 24mil without edge pullback, blistering for pitting—the lat-ter of which has plagued the ENindustry for years. For the purposesof this article, we are using a RoHS-compliant high phosphorus (10-12%) electroless nickel, as it is themost commonly used for high-build applications.

The most common causes of pit-ting (MCCP) are as follows:

1. Particulate matter that is air-borne or dragged in by sub-strates (i.e., dirt, soap, oil, cutting solutions).

2. Foreign matter sticking to the substrate (glass bead, alterna-tive substrates trapped in the porous surface, etc.)

3. Particulate matter formed in solution—nickel which has “plated out” on itself or on thetank.

4. Gas Pitting—air bubbles attachto the substrate, not allowing the solution to reach the surface of the part.

Problems created by MCCP num-bers 1 and 2 can be eliminated by ver-ifying that pretreatment proceduresand operating parameters are beingfollowed per the requirements of aparticular substrate.

Prefered Steel Pretreatment1. Soak Clean—time will vary

with part/substrate to achieve a water break free rinse

2. Rinse3. Electroclean—30 seconds to 5

minutes (Don’t burn the parts)4. Rinse5. HCL based activator—30

seconds to 2 minutes6. Rinse7. DI Rinse8. RoHS Electroless Nickel -

Prefered Aluminum Pretreatment1 Soak Clean—time will vary

with part/substrate to achieve a water break free rinse

2. Rinse3. Caustic or Acid Based

Aluminum Etch—time will vary with part/substrate

4. Rinse5. Aluminum Deoxidizer—time

will vary with part/substrate6. Rinse7. DI Rinse8. Aluminum Zincate—1.5

minutes9. Rinse10. Zincate Strip—10% Nitric Acid11 DI Rinse12. Aluminum Zincate—1.5

minutes13. DI Rinse14. RoHS Electroless Nickel -

Easy Tips to Eliminate MCCP 1 &2:

• Constantly filtering solution via a 1 or 5 micron filter will help eliminate Ni-based particulate matter created in the tank through plate out.

• Use substrate specific media ifparts require blasting prior to pretreatment (example: Do not use the same media for steel and aluminum).

• Overly aggressive pretreatment can actually create more pitting issues. Be sure to verify that the substrate is not damaged in thepre-treatment process.

TECHNICALLYspeaking

BY JAMES WETHERALD, TECHNICAL SALES REP, RONATEC, C2C,INC., CARLSBAD, CALIF.

Fig. 1. (Top view) Mild solution agitation via eductor angled off the wall of the tank then onto the part.

most important part of the processwas actual tank configuration. Pleasenote that air agitation is not recom-mended for this process. The bestresults were found with the follow-ing configuration:• Mild solution agitation (approxi-

mately 1 tank revolution per hour) via eductor angled off the wall of the tank then onto the part. See Figure 1.

• Solution filtration should utilize a 1 micron poly pro filter. Filter bags are preferred.

• Solution should be filtered at a turnover rate no less than 10 times per hour.

• Part needs to be mechanically agitated. Our study showed that best results were achieved when the part was lifted and dropped in order to release air bubbles that attach to the substrate’s surface, thus eliminating “gas pitting.”

• While lifting/dropping the part was moved side to side. The studyused an agitator rod moving at

20 RPM with a “falljoint” of 2.25 inches.

Reactivation. In someextremely high-buildapplications, reactivationof the part may berequired as the EN sur-face can become passive.This can be very useful ifparts are going to be

“ground down.” after plating.Reactivation can only work if thecause of the pit is removed during thereactivation process. This can bedone in a number of ways. Researchfound that for parts with buildrequirements over 10mil can be:

• Taken out of the EN solution• Rinsed• Exposed to an low amperage

electrocleaner for 5-15 seconds• Rinsed• Reactivated in a 30% by volume

HCL solution for 10-15 seconds• Rinsed• Rinsed• Put back into the EN solution

Assuming that the pretreatment isperfect, we can then address the actu-al EN tank and chemistry (SeeMCCP 3 and 4).

RoHS compliant. Extensive testinghas found that using a non-RoHS-compliant solution is difficult. Thelead and cadmium found in tradi-tional EN solutions cause the EN to“plate out” on themselves faster thanthat of their RoHS-compliant coun-terparts. Our study showed thatachieving a thickness higher than7mil with non-RoHS-compliantsolutions was not possible. We alsonoted that using material designedbefore the “1-to-1” era of electrolessnickel proved difficult, as differentcomplexor packages limit the stabili-ty of the solution.

EN Manufacturing. The nickel com-ponent should be of the purest qual-

ity. We have found that by filteringthe nickel component at our manu-facturing facility (through a 1micron filter) decreased internal par-ticulate pitting by 41%.

EN Chemistry. We noticed thatoptimal operating parameters areslightly different than those utilizedwith traditional high-phos EN plat-ing. By lowering the pH to 4.6, keep-ing temperature at 188°F, and nickelconcentration between 98-101%,results were conclusively superior tomultiple alternatives. Note: This mayrequire chemical additions as oftenas four times per hour.

Tank Set-Up/Configuration. The

Note: It is advisable to do this every4 hours after the 10mil point isreached.

Additional wetters—Wetting agentswhich reduce the surface tension ofthe part can be made available bymost EN suppliers. Research showedthat these can assist in a pit-free sur-face, on occasion.

Substrate—Parts that showextreme “outgassing” during theplating process will be difficult topast 2mil. This will change with thesubstrate composition.

CONCLUSION We hope this information helps withany high-build applications youhave. This information is based on acollective analysis of our team, butwe are always looking to expand ourknowledge and appreciate your sug-gestions. Please contact Ronatec at(760) 476-1890.

BIOJames “Jim” Wetherald serves as a tech-nical sales representative for theElectroless Nickel Division of Ronatec,C2C, Inc., based in Carlsbad, Calif. Heworks closely with direct customers anddistributors addressing issues with a“hands-on” approach. Jim graduatedfrom San Diego State University withdegrees in Integrated Financial Systemsand Applied Mathematics, and he hasstudied chemical engineering and JITsystems management.

REFERENCES1. Please visit http://www.metalfin-

ishing.com/mf/ask-the-experts/james-wetherald/recentfor Ronatec’s preferred pretreat-ment of various substrates.

TECHNICALLYspeaking

Figure 2. Side view of EN plating

40 I metalfinishing I May 2012 www.metalfinishing.com