Q) My questions relate to silver and gold plating of aluminum parts:
We are in the Microwave and RF microelectronic communication industry.
I am trying to develop questionnaires that will help me determine the required characteristics of a reliable plating house.
I am seeking information on the essential processes, which type of plating typically produces less defects (electroless plating or electroplating), sources to learn more about plating, etc.
Can you send me any documents, suggest people or organizations to call, etc.?
A) Thank-you for your question.
In my opinion, the basic elements of a reliable plating facility can be summed up in two words? “ Knowledge ” and “control ” . The trick is to create a questionnaire which accurately captures these elements, and in particular how they are applied to your parts.
As you suggest, a better knowledge of the processes used when plating aluminum with silver and gold would certainly be an asset. Be aware that while resources exist to help you learn more about these processes, it is unlikely that they will make you an “ instant expert ” in plating.
There are a host of resources available, but I urge you to take advantage of the AESF Foundation training courses. The National Association of Surface Finishing (NASF) website gives you an overview of available training here.
This website also has an excellent section located here on available training.
Local resources are most likely available to you. The best way to take advantage of all of these resources is to become active in the NASF, or in your local organization. Click here to a link to these organizations.
Finally, click here for a link to our annual trade show, where you can find a virtually anything related to surface finishing.
Q) We have a captive EN plating department and moved into a new plating facility in March of 07. The new tanks are virgin polyproplen and were cleaned per the procedure provided by Palm Int. After three new baths we failed the 100 hour salt spray test on a 4" x 6" mild steel test panel coated with .0015" of mid phos EN. The samples had two very small indications of failure. In review of our process with the chemical supplier we are doing everthing per the book for error free plating. Yet we failed the salt spray test.
If you have any insight to what could be causing the defect I would appreciate any suggestions.
A) Thank-you very much for your question. I am assuming that you used to meet this requirement, but have failed it since you moved your plating department.
The first thing I would do (if you have not already done so) is to verify that you do have a problem by repeating the salt spray test. If you get another failure, then look for sources of particulate matter getting into the plating tank, since salt spray failures are due to porosity in the coating. The devil is finding the root cause of the porosity!
Since you moved your entire plating operation, I’d recommend you pay particular attention to the differences in the two plating systems, such as the process chemistry, rinsing, water source, process sequence, dwell time, plating bath filtration, surrounding environment, etc. Below is a chart outlining the more common causes, which may assist you in locating the root cause of the porosity.
COMMON CAUSES OF PITTING |
MECHANISM |
Suspended solids |
Particles in the bath are a common cause of pitting. If the particles stay on the work, they cause roughness. If they fall off, they cause pitting.
This pitting is usually seen on shelf areas. |
Contaminated bath |
Organic contamination is a leading cause of pitting. This type of pitting looks unique—usually a spherical dimple in the plate, typically on the underside of the parts.
Filter bags and cartridges are a common source of organic contamination. Leach filters in dilute sulfuric acid prior to use.
Low organic stabilizers can lead to pitting. Copper and nitric acid consume sulfur stabilizers |
Porous or pitted substrate |
Electroless nickel will not typically fill in voids in the substrate, resulting in a pitted deposit. |
Poor pretreatment |
Poor pretreatment cycles that leave oils and organics on the work can cause pitting. |
Gas pitting |
On thick deposits gas pitting is a major problem.
Reducing the surface tension usually helps.
On the sides of the work it causes “fish eye” pits. |
Low complexors
|
Low complexor allows the formation of nickel phosphite and nickel hydroxide. |
Additions made directly on top of parts
Make-up or replenishment
chemistry mixed together prior to adding to the bath
|
Chemical additions made directly on top of parts or mixing the replenishment chemistry together prior to adding to tank can form nickel hydroxide particles, which will eventually dissolve and leave a pit behind. |
To reduce or eliminate pitting, I’d recommend the following:
1) Improve filtration - Ten to 15 solution turns/hour through a 1 micron filter.
2) Change the filters frequently, and leach the filters prior to use in dilute (0.5 to 3% by volume) sulfuric acid to remove tramp organics.
3) Maintain good housekeeping on the line.
4) Maintain good chemical control of the bath. Look for oil on the bath and on the tank walls. Look for foaming in the electroless nickel bath.
These are signs of organic contamination.
5) Pay attention to the pretreatment. Check the parts prior to plating.
6) As a last resort, use additives in the plating bath, such as a wetter or a dispersing agent.
Q) My name is Leon Vernovsky. I'm Estimating Engineer at Micro Stamping Corporation.
One of Medical customers send me request for quote. It is stamped part made of 316L Stainless steel. This part is Post-plated (on the print) with Platinum / Iridium 80/20. No thickness of plating. I have feeling that it is a mistake.
My question is: Does this type of plating exist? If it does, may be you can recommend me a Comnpany which can make this coating and I'll send them request for quote.
Thank you.
Leon.
A) Mr. Vernovsky: The elements ruthenium, rhodium, palladium, osmium, iridium, and platinum are commonly referred to as the platinum group metals, or PGM. They all have comparatively high melting points, and all are very inert. Many of these elements have found widespread use in various industrial, electronic, and commercial applications. Often they are alloyed with each other to enhance their performance.
There is widespread use of platinum-iridium compounds for medical devices due to the advantages it offers. Iridium is typically added to the platinum from 5 to 20% by weight to increase the hardness of the resulting alloy. Since the alloy is very inert, it does not react or corrode inside the body. The incidence of allergic reactions to this alloy is extremely low. Also, the electrical conductivity of the alloy is good, making it an excellent choice for an electrode.
One of the more common uses is for pacemakers, which use platinum-iridium coated electrodes to pass electric pulses to stabilize the heart’s rhythm.
Another heart related use is for internal defibrillators, which will pass an electric charge to the heart.
Platinum-iridium alloys are also commonly used for stents and catheters.
The inert nature of the alloy as well as the fact that it is quite opaque to x-rays (allowing doctors to keep an eye on the implant) makes this an excellent choice for these applications.
When discussing platinum-iridium plating the first thing that comes to my mind is jewelry plating. Platinum-iridium alloys are commonly used in plating jewelry, due primarily to its white deposit color, relative hardness, and its ease of soldering, welding, and brazing.
Platinum-iridium alloys are also used for spark plugs, where they reduce the spark wear of the plug and prolong its life.
You should confirm the alloy content, as 80/20 platinum/Iridium can refer to either mass or volume (which coincidently in this case are similar, but not exact), as well as in regards to deposit thickness requirements.
Q) I plate parts for several different customers, most of which have contracted pricing. Needless to say, the price of nickel metal is killing me. I have very little leeway on my contracts until next year, but I need to do something to reduce costs now. What options do I have to reduce my nickel usage?
A) Oh, Boy! This is one hot topic, and I could write a book on the subject. I will try to give a concise yet informative answer, but be aware that the methods below are by no means all inclusive. Also, you do not specify what type of nickel plating system you are using, so I will answer for both electrolytic and electroless nickel products.
For the sake of simplicity, conserving nickel can be grouped into three main categories:
- Recovery
- Reduction
- Substitution
Recovery consists of minimizing wasted metal. Spray rinses over process tanks, recovery of the plating solution by a drag out tank, and modifying the plating cycle to include longer drip times over processing tanks are a few examples of commonly used recovery methods. There are potential complications, which include diluting the plating process, the introduction of microorganisms which can grow in recovery tanks, and increased potential for cross contamination of the plating systems.
Another recovery method which is becoming more popular is reclaiming nickel by utilizing ion exchange or electrowinning. Many ion exchange methods offer a process to convert the recovered nickel into a salt suitable for use in the plating bath. Contact your chemical supplier to see if they offer this type technology.
Reduction refers to lowering the metal content of the plating processes. By running the plating process at lower metal content you automatically reduce the drag out losses. This technology is available for both electroless nickel as well as electrolytic nickel. Care must be taken when changing the basic operating parameters of your plating bath, so consult your chemical supplier prior to making any major changes.
Substitution refers to replacing a portion of the plated nickel with something else. There are a host of commercially available options, such as nickel-iron alloy plating. This technology can successfully replace electroplated nickel in most applications. Another substitution method for electrolytically deposited nickel is to use multilayer nickel coatings. Using multilayer nickel allows an overall reduction in deposit thickness while still offering the same or better corrosion performance on a part while using substantially less nickel.
The first step in your nickel cost reduction strategy should be a detailed audit of your existing plating lines and processes to quantify the amount of nickel wasted by drag-out losses. Next, consult with your customers and determine their willingness to consider alternative coatings, alloys or substitutes. Finally, enlist the assistance of your chemical supplier and other technical resources to determine the best course of action and alternatives to recover, minimize or eliminate the loss of your nickel metal throughout your process. |
