مقالات آنالیز و کنترل در آبکاری

troubleshooting, testing & analysis
TROUBLESHOOTING ELECTROLESS NICKEL
APPLICATIONS

BY JAMES WETHERALD, TECHNICAL SALES REPRESENTATIVE, ELECTROLESS

NICKEL DIVISION OF RONATEC, C2C, INC., CARLSBAD, CALIF.

Q: I have been told that passivating 13-8ph material prior to electroless nickel plating willcause problems with adhesion. Is this true, and if so, why?

A: I am very familiar with electroless nickel plating over stainless steel. I havealways passivated with HCL prior to plating. I would like to see a Woods nickelstrike used between passivation and electroless nickel plating. If you are tryingto activate bare stainless in the electroless nickel tank, you will need to use anelectrolytic start for a few seconds so the stainless surface will begin plating.

Q: Can a gold pattern with isolated features on a ceramic substrate (Pd activated) beelectroless nickel plated and pass tape test?

A: Please note that you cannot plate EN top of gold. Gold, like lead, is a poisonto EN and it is not autocatalytic. Putting palladium on top of gold may make itplate, but adhesion will be poor.

Q: Could you point me to a method for determining the % phosphorous in a thickness testpanel from the electroless nickel process?

A: 1. Analyzing phosphorus percent with ICP and AA are very inaccurate due tointerferences and the form that phosphorus is in (phosphides). We haveboth seen very low and very high (chemically impossible) phosphoruslevels from these methods.

2. X-ray analysis also gives inconsistent values due to the localizednon-uniform distribution of the nickel phosphide complexes at thesurface-meaning two local areas could have a higher and one lower phosphoruscontent, when the average of the Ni-P matrix is somewhere inbetween those two values.

3. All major EN suppliers have found that there is only one consistent wayto analyze phosphorus percent. Using a spectrophotometer, the lightabsorbance of phosphorus is measured, which has a linear relationshipto the percent of phosphorus in the deposit. This method is accurate andrepeatable.

Q: I am trying to find out the proper way to activate Thermcon 83 prior to placing partin an electroless nickel tank. The material is 25% copper and 75% tungsten. Do you haveany suggestions?

A: I am assuming you are using a RoHS-compliant electroless nickel (doesn’thave lead or cadmium)?Tungsten can be tricky, and my experience has been limited with it whencombined with copper. With that said, copper should act as a conductoronce “set off ” so I would suggest either an electrolytic strike (Woods) prior toyour electroless nickel tank or electrolytically charging the electroless nickel byrunning negative current to the part and positive current to the solution with asmall rectifier for 15 seconds (maybe less).Just a quick note on electroless nickel over 100% tungsten: It should beactivated with a diluted percentage of palladium chloride. We are not doing sohere as we have 25% copper in the substrate.

Q: We have a sink that is hand hammered copper, plated with nickel and brushed. Weare experiencing a problem with the sink discoloring and turning black. It can be cleanedand polished, but the black returns. I understand this comes from a problem in the platingprocess. Can you help me understand that?

A: I have actually faced this exact issue in the past. (I am assuming that youare referring to electroless nickel when you mention nickel?) A great way toresolve it is by using an electroless nickel with a slightly higher phosphorouscontent.It sounds like you are using either a low phosphorous or “low-medium”phosphorous electroless nickel on these sinks. What is happening is that the lowpH(a.ka. acidness) of the water or tomato juice – or whatever else you are puttingin the sink – is reacting with the low-phos of the electroless nickel, causingit to turn black. By increasing the phos content to over 7% you should be ableto eliminate the problem. Either way, the plating process sounds fine – you justneed a bath with higher phos content.

Q: We are having pitting/porosity issues with our high-phos electroless nickel process. Afterextensive testing, we found the pitting begins after 0.004" of deposit. This is a problem whenwe need to build up to around 0.020" . I feel like we’ve tried everything. Do you have anysuggestions on how to stop this?

A: Please check the following: pH, temp, Ni concentration, and plating rate.Assuming that you are using a standard semi-bright, high-phos electrolessnickel, I would like to see your temp dropped to 183°F, pH at 4.7, and nickelconcentration at 100% of manufacturer’s recommendation. This will slow yourplating rate, which will help increase high build without stressing the surface.We might even let the pH drop to 4.5 later.It is also possible that you have contamination in the bath or in your pretreatment.Please check for nitric in the electroless tank with nitric test strips (makesure they are not old). Also, shut off all agitation to the pretreatment baths(including rinse tanks), wait 5 minutes, and check for oil slicks at the solutionsurface. If you have oil, you will have pits. Try “spray rinsing” to avoid the rinsetanks and see if this helps as a test.Also check your concentrations while plating. It sounds like the pitting is happeningat around the first hour mark. Do you replenish while in production? Ifnot, you are plating too much of the wetter out of the bath while plating. Youshould be replenishing while in production for thicknesses which require over 1hour of plating. TIP: Make sure you add the “A” or nickel component first, thenthe “C” or hypo/stabilizer component.If the substrate is aluminum: Are you using a caustic or acid-based etch? Iwould recommend an acid etch for most high build/high-phos applicationsto avoid porosity at the part’s surface, which can lead to hydrogen “leakage” ataround 1 hour of plating.

Q: What is the ideal post-plating treatment over high phosphorus EN plated regions ( apartfrom local removal of phosphorus) that need to receive tin-copper solders? Should regionspecificbronze plating be tried?

A: A fluoride pickle is always recommended before soldering an EN coating.However, an RMA (rosin mildly active) flux will allow you to solder to anyphosphorus type EN. Fresher plated EN is also preferred, if given the choice, toreduce oxidation of the nickel surface.

Q: I have a question about mid-phosphate electroless nickel: How many hours (salt spraytest) are required to pass with 15 micron thickness? We are plating over aluminum 6061,and we require 48 hrs of salt spray test to pass. Note: Any white spots on the component willbe rejected after salt spray test.

A: The standard for most mid-phos electroless nickel is 100hr salt spray protectionwith 1mil of thickness. Over 6061 aluminum, you should not see anywhite spots after testing. Note: not all electroless nickels are created equal. Pleasecontact me if you need information on a product that is guaranteed pass your48 hour test (standard for the aerospace connector industry).

ABOUT THE AUTHOR

James “Jim” Wetherald serves as a technical sales representative for the ElectrolessNickel Division of Ronatec, C2C, Inc., based in Carlsbad, Calif. He works closelywith direct customers and distributors addressing issues with a “hands-on” approach.Jim graduated from San Diego State University with degrees in Integrated FinancialSystems and Applied Mathematics, and has studied chemical engineering andJIT systems management. Ronatec works with facilities across the United States,Mexico, Canada, China, Brazil, Thailand, and Ireland. Ronatec operates warehousingfacilities in eight convenient locations, providing shipping on a same-day basis. For more information, please call (760) 451-9081 or visit www.ronatecchemical.com

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