I am Debbie Aliya and I run a small materials consulting service. I am working on a project which involves a small electronic gizmo that has a component with a gold plating layer over (probably electroplated) nickel which is over stainless steel.
SEM/EDS revealed the presence of a trace of silicon along with the gold in areas that were damaged potentially due to local overheating due to intermittent contact.
I am aware of the silicon peak interference with a minor gold peak position in the EDS. However, the PROBLEM area had a distinct VISIBLE SI PEAK (very small, but distinct) whereas the NON PROBLEM AREAS had no trace of silicon.
The trace of silicon appeared BOTH on the surface in the damaged area AND in the core of the plating thickness when tested on a cross section.
I am wondering if anyone knows anything about silicon potentially being a contaminant in a gold electroplating process.
Debbie Aliya consultant - Grand Rapids, Michigan, USA
Debbie, Silica is the first contaminant that comes off of a DI column as it becomes exhausted - so perhaps the plating company was using bad DI water to replenish the gold bath.
Pat Mentone St Paul, Minnesota
Yes, I heard of it....it could be from:
1. The degreasing, degreasers often contain silicates, especially the older formulas.
2. A surfactant. There are surfactants used, either in the electrolytes or sometimes in the final rinsing steps, that could contain silicon.
3. Other possibility is a DI installation, nearby the regeneration point, which could already release silicon in the rinse-water (non-conductive, so no increase of conductivity yet.)
Easiest way to go is to contact the supplier of the parts and ask them (be willing to sign a NDA) if they use a cleaner with silicates, any surfactants containing Si anywhere in the process and what the trigger for regeneration of the DI installation is. Sorry to say, but don't take a "no" for granted, sometimes people even don't know themselves.
But be also aware as that the fact that it's used, doesn't mean that it should be the source for your specific case.....as:
4. Silicon could be present in the base-material (e.g. in the simple form of sand-particles, or as silicon oxide, formed from Si present in the alloy. Many alloys contain purposefully Silicium) and on a Si-rich area you could have a pore after electroplating and these pores can have liquid spotting out.
Harry van der Zanden - Budapest, Hungary
May 9, 2011
Thank you very much.
Sorry it took so long to answer.
Life has been crazy in the last 8 months.
I am glad that there is a reason that I was finding these traces of Si in the Au.
Debbie Aliya - Grand Rapids, Michigan
(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)
Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.
If you are seeking a product or service related to metal finishing, please check these Directories: