Electroplating was developed as a combination of Direct Current (DC) and a chemical bath. It was understood that this simple waveform and bath composition had considerable limitations. Numerous innovations followed to optimize the plating process for the desired deposit characteristics. There were advances in cell geometries, anode materials, temperature controls, monitoring, instrumentation and numerous others.

A key advancement was the use and optimization of chemical additives for the DC electroplating bath. We recognize the need to change our bath (electrochemical process) based on the required deposit characteristic (i.e. throwing power, flatter deposit, conductivity, etc.). Additives change the process parameters and mediate the desired results.

Performing the electroplating operation as a process (sequence of steps) enables us to properly level complex parts (such as PCBs) and achieve otherwise difficult deposit characteristics. For example, at a specific point during electroplating, we need to utilize an exact quantity of a specific additive. A second example is to stop the plating process, mask the section which was just plated, unmask another section to be plated in the next step of the process, and continue on. The point is that electroplating was developed and successfully utilized by creating processes. A process allows the user to accomplish the task by performing multiple measurable steps each specifically defined to yield a desired result. The sum of the incremental steps is a completed process with a desired result.

The timeless truth I referred to in the subhead is that “electroplating needs to be viewed and executed in terms of processes, regardless if it involves DC or pulse waves. This is especially true as our work pieces are composed of multiple geometries (fine-line traces, vias, PTHs) requiring multiple deposit characteristics.”

Somewhere in our search for continuous improvement, six-sigma quality, and reduced cycle time, we discovered pulse plating and forgot that timeless truth. Thus began our search for the “magic pulse waveform.” You know the one. You set your dials on this waveform and electroplate fine-lines, plated though holes (PTHs) and blind vias with bright deposits and high conductivity using any proprietary chemistry and additives developed for DC. The only reason we cannot find the magic pulse waveform is that those who have it will not share the information with us. We keep looking and waiting for someone to demonstrate it so that we can upgrade our plating operations.

We would not attempt to drill different sized holes with a single drill bit. Nor should we attempt to electrochemically fill different sized holes with a single pulse waveform. This approach is similar to our ancestors frustrated search for the mythical fountain of youth; they returned after several centuries with increased value placed on the old knowledge. Prior to the search for the fountain of youth, that knowledge consisted of a healthy diet, genetics, hygiene and exercise, to name a few.

Today we know to value diet, genetics, hygiene and exercise in the pursuit of a long and prosperous life. The pursuit of such ideal solutions is not itself bad; it motivates us to pursue a noble goal. What we find, however, may not be what we expected. In the pursuit of the fountain of youth, through medicine, technology and other efforts, we have in fact extended our life expectancy considerably, eliminated many deadly plagues, and are now stronger and healthier than at any other time in history. Clearly, we’ve not reached the ultimate goal, nor are our methods that which Juan Ponce de León expected to find in the 15th century, but it all adds up to a longer and more prosperous life.

Similarly with electroplating, as we search for a magic pulse waveform, we advance technology and solutions. This is not as effective as if we had the end goal in mind at the start, but it is progress, and these advances benefit our manufacturing capability and bottom line.
There are many modern examples to indicate that we will not find the magic pulse waveform, but rather, the need to incorporate new pulse technology with the old wisdom of performing the job as a process or sequence of steps. The sum of these tangible steps can yield a more efficient and higher performance process while providing time and cost reductions.

Faraday Technology, during IPC 2000, demonstrated a single waveform was not optimally able to geometrically level both PTHs and blind vias. This is important if we hope to reduce process time and cost by eliminating multiple plating baths.

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Traditional electroplating of such components as bearings, pistons, andlanding gear parts often results in an uneven finish as well as wastageas the plating technician tries to achieve uniformity through grindingand polishing. HNKTech’s FEA software works by creating a densitymodel. The model is displayed after inputting your electroplatingset-up including the geometric profile, material properties, andboundary conditions. Using these variables, the software simulates theelectroplating process then displays the density model with predictedplating thickness and uniformity.

Engineers can review the density model and make changes to thepositioning of the jig, voltage, time, and temperature. The simulationis re-run until the engineer is satisfied with the thickness anduniformity predicted. The company says that the variation in thicknessand uniformity between what is predicted and what is achieved in thefactory is 95% accurate.

HNKTech’s software uses a customized user interface that is said to beeasy to use. No specialist training is necessary and even thosewith limited training can use the software effectively, according tothe company.

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First things First
Quick solutions to problems on an electroplating line can save thousands of dollars. Experience is by far the most valuable tool a troubleshooter can possess. So successful troubleshooting begins when the line is at its best! Build your experience by walking the line when everything is running smoothly. Take note of solution color, smells, gage settings, etc. Intimate knowledge of your plating line and its idiosyncrasies will expedite the solution to future problems.

Now that a problem has developed, you must walk the line looking at temperature gages, current, anode baskets, pumps, etc. You must rule out the cleaning section of the line and the post plate section of the line. These steps may take some time but they must be done. Ninety five percent of plating problems have nothing to do with the plating bath. Occasionally a problem develops, though, which persists despite experience.

Into the Lab
Once the problem has been determined to be a result of the plating solution or the material being coated, the troubleshooting should be done in the laboratory.

Before starting a laboratory investigation, the first thing to do is ship samples of the plating bath and reject work to your supplier. Suppliers often have sophisticated labs with experienced people. Follow up with a phone call to your supplier. Speak directly with a technical service representative and discuss your problem and investigation.

Once in the laboratory, define the condition of the bath with a routine analysis and a routine hull cell. Correct any chemistry problems found by the routine analysis. The routine hull cell should be one you re used to looking at. Suggested conditions for a routine panel are:

1. A two amp, five minute, unagitated panel for acid zinc.
2. A one amp, ten minute, agitated panel for alkaline zinc.
Compare the routine hull cell panel to ones from when the problem was not present. Measure thicknesses across the panel and again compare them to past hull cell panels. If the routine hull cell panel appears normal, chances are your problem lies outside of the plating bath. Re-walk the line and review your observations. Pay particular attention to the electrical portion of the plating bath, as poor electrical connections will make the plating bath appear to be at fault. Investigate the material of the parts exhibiting the problem. Again, material problems will not manifest themselves in the lab. If you are still convinced that the plating bath is the source of the problem, continue with the lab investigation.

The next step is to use a hull cell to generate the problem. Make sure the conditions and time all hull cells were run are clearly marked on the resulting panel. Vary the conditions in the hull cell to give yourself the best opportunity to produce the problem. Some variations, which may prove useful, are:
1. Panels run at low amperage
2. Panels run at high amperage
3. Bent panels to create a shelf area
4. Bent panels to create an extreme low current density area
5. Panels run at a high temperature
6. Panels run for thirty minutes then scribed with an exacto knife (to reproduce blistering Knowing how your bath appears when operating normally will make the interpretation of these hull cells easier. Once the problem has been produced, we can proceed to the next step.

Target Identified
With the ability to produce the problem, one now needs to know how to remove the problem. The problem probably will fall into one of several broad categories:
1. Organic contamination
2. Metallic contamination
3. Poor filtration
4. Imbalance of proprietary chemicals
5. Unknown

With an unlimited supply of solution, take the opportunity to begin multiple treatments. After each of the following treatments, rerun the hull cell test, which produced the problem. First, for organic contamination, treat three hundred milliliters of solution with two grams of activated carbon. Mix the solution continuously for at least thirty minutes, then filter and run the hull cell. Second, for metallic contamination, treat three hundred milliliters of solution with one-half gram of zinc dust. Again, mix the solution continuously for at least thirty minutes, then filter and run the hull cell. Third, filter the solution thoroughly. The solution must be clear after this step. Use a filter aid if necessary. Fourth, if the solution is an acid bath, metallic or organic contamination may be affected by adding one tenth of a gram of potassium permanganate to three hundred milliliters and mix the solution for five minutes. Filter thoroughly and run the hull cell. For an alkaline solution, freeze out carbonates by putting three hundred milliliters in a lab refrigerator. Cool the solution to 30….F for fifteen minutes. Decant the solution, raise the temperature, and run the hull cell test. If one of these treatments affects the problem, you may be well on your way to solving the problem. Give yourself a pat on the back! Not too fast though. You now must translate the lab results to the production line. You must also locate and eliminate the source of the contamination. The quick results in the lab may take a couple of days to accomplish in production. But don t give up. Plug away until the job is finished.

Unknown
If the above treatments did nothing to affect the problem, things just got a lot tougher. Get on the phone to your supplier and ask for their assistance on-sight. Review their analysis of your bath. Is your bath low on carrier, high in brightener, out of balance, etc? Many suppliers have doctor solutions. By comparing notes with your supplier, they will be able to send in a new arsenal of weapons along with technical assistance. Meanwhile, there are still a few hull cells to run:

For an alkaline bath try:
1. Adding 1% sodium
hypochlorite to the hull cell
2. Adding one-half ounce per gallon of EDTA or Rochelle salts
3. Diluting the bath by 25% with virgin solution
For an acid bath try:
1. Heating the bath above the cloud point, then carbon treat
2. Reduce the pH of the solution with 50% hydrochloric acid to kick-out most organics.
Usually a pH of 2.5 is sufficient. Filter the bath, raise the pH, and add carrier.
3. Diluting the bath by 25% with virgin solution
Out of all the tests you have now run, hopefully something you can build on has emerged. If not, you are into the rare problem, which falls into the unknown classification. This type of problem will take time and effort to resolve. Calling in electricians, sending samples to outside laboratories, etc. are examples of the steps that may be necessary to solve the problem. In this case, the economics of dumping the bath and making a new one must also be considered.

Conclusion
Troubleshooting a zinc-electroplating bath will be much easier if one takes the time to observe the line when things are running well. When a problem develops, split the line into a pre-cleaning section, the plating bath, and a post-plate section. Run tests to isolate the problem to one of the three sections. When the plating bath is identified, follow these steps:
1. Send samples and reject parts to your supplier.
2. Use the hull cell tests outlined above to treat the problem. Remember, even if you can treat the problem, you will also have to eliminate the source of the problem.
3. Demand prompt service from your supplier.
4. Label or identify all tests run during the troubleshooting process.
Once the problem is solved, go back and review the troubleshooting process and learn from it. This will build your troubleshooting skills and shorten the duration of future problems

With the study of zinc electroplating process by Electrochemical Noise (EN), it was found that the EN generated during the electroplating of large conglomerate zinc deposit has large potential oscillation amplitude and positive potential drift. However, small noise amplitude and little potential drift was seen in the case of compact zinc deposit. Any metal can be plated through zinc electroplating process, but the most common are steel and iron, on which the process offers sacrificial protection.

Steps of Commercial Zinc Electroplating Process
On the commercial scale, zinc electroplating is done by the following steps.
1. Surface of the metal is cleaned in alkaline detergent type solutions, and it is treated with acid, in order to remove any rust or surface scales. Cleanliness is essential for successful zinc electroplating, as the molecular layers of oil or rust can prevent adhesion of the coating.
2. Next, the zinc is deposited on the metal by immersing it in a chemical bath containing dissolved zinc. A DC current is applied, which results in zinc being deposited on the cathode. Alkaline zinc baths are used by the finished products, to produce a more consistent zinc thickness, especially in recesses.
3. Hence an increased protection from corrosion is provided, as the corrosion of the deposited zinc is reduced. The zinc coating can increase the time required for the formation of white rust, by ten times. Finished Products also apply sealers, which are now commonly being specified by the automotive industry, further increasing corrosion protection.

It is very difficult to obtain a uniform thickness of coating, with electroplating technique. The thickness of the coating is very much dependent on the geometry of the object being plated, and it is preferentially on the external corners and protrusions of the metal body, hence not much of it is deposited on internal corners and recesses. Zinc electroplating process is used to make a clean, smooth and corrosion resistant surface. It also makes an excellent undercoat for powder coating or paint and can leave recesses on complex shaped components without sufficient zinc coating, in order to provide corrosion protection.

The process of electroplating (also referred to as electrodeposition) is fairly simple. To start, a negative charge is placed on the object that will be coated. The object is then immersed in a salt solution of the metal that will be used to plate the object. From there, it’s simply a matter of attraction; the metallic ions of the salt are positively charged and are thus attracted to the negatively charged object. Once they connect, the positively charged ions revert back to their metallic form again and you have a newly electroplated object.

Controlling the thickness of the electroplated object is generally achieved by altering the time the object spends in the salt solution. The longer it remains inside the bath, the thicker the electroplated shell becomes. Of course there must also be an adequate amount of metallic ions in the bath to continue coating the object. The shape of the object will also have an effect on the thickness. Sharp corners will be plated thicker than recessed areas. This is due to the electric current in the bath and how it flows more densely around corners.

Before electroplating an object, it must be cleaned thoroughly and all blemishes and scratches should be polished. As mentioned, recessed areas will plate less than sharp corners, so a scratch will become more prominent, rather than being smoothed over by the plated material.

The process of electroplating began at the beginning of the 20th century and continues to evolve today. Many common objects such as tin cans are actually electroplated steel with a protective layer of tin. Medical science has experimented with electroplating to create synthetic joints with electroplated coatings, and new advances in electronics have been made with electroplated materials.