Copper plating is the electro-chemical process involving the permanent deposition of a copper layer on a metal. It’s more of a finishing touch on metals to foster durability or add an aesthetic appeal, but other essential benefits exist. The process is straightforward but quite sequential, involving a few steps that need utmost care and precision for high-quality output. Copper plating is a mainstay and incredibly essential in the contemporary oil and gas industry. Still, other manufacturing sectors find this process incredibly practical, making it a pillar in virtually every metalwork process. This article explains the four copper plating steps you should know about.
Copper Plating Overview
Copper plating has been quite a rudimentary process familiar to the manufacturing industry since the early days of the industrial revolution. It’s become one of the essential metal finishing processes, giving metal a better aesthetic value while ensuring incredible durability. This process is sequential and involves massive electric currents, especially on the industrial scale. The idea is that plating metal using electric current makes it a more permanent method than simple painting. That’s made this process more preferred by manufacturers globally, stamping its presence for a while. Remember that the copper plating process isn’t one-fits-all but involves various techniques.
Main Copper Plating Techniques
Copper plating uses various techniques, all aiming at similar results. However, this disparity in these techniques depends on the access to the resources available and the time needed to complete the process. Here are the leading copper plating techniques you should be familiar with.
Dual Damascene Plating
This technique uses bottom-up copper plating where the accelerants, suppressors, and levelers work together. It prioritizes specific features on a metal part rather than the entire cathode and is incredibly useful in electroplating semiconductors and other tinier components. Given the expected result, this process isn’t widespread since most copper plating applications apply to entire metals.
Through Silicon Via Plating (TVS)
Like the dual damascene plating, this technique targets specific metal parts. However, the difference is that they electroplate more significant features and are somewhat slower. This technique is essential for high aspect ratio requirements and is ideal in interconnect technology like the stack, MEMS devices, CMOS image sensors, and 2.5D interposer architectures.
Copper Pillar Plating
Copper pillar plating is ideal if you don’t want to compromise on uniformity. However, it’s a pretty complex process but can be a bit quicker than TVs. It uses moderate polarizing agents as suppressors and low to medium accelerator concentrations, allowing no trade-offs on plating uniformity. The process is ideal for large-scale copper plating and industry sectors unwilling to compromise on uniformity.
Redistribution Layer Plating (RDL)
Like copper pillar plating, this technique promises much uniformity and precision of about 2 µm. This technique is ideal for advanced integrated circuits having fan-out and fan-in wafers. You can apply this process in either 2D or 3D methods since either is cost-effective and incredibly practical in giving metals their deserved copper coatings.
The Copper Plating Solution Steps
While various copper plating techniques exist, the idea is only similar. Copper plating uses a simple structure you can only see from a minimalist angle, where no complexities come into play. The results are usually identical but differ in quality, uniformity, and thickness. Here are the general copper plating steps you should know about.
Step 1: Choosing The Best Electrolytes
This process may require significantly huge electrolyte volumes spanning thousands of liters for large-scale electroplating. However, the process is similar in spite of the scale of preparation. Universally used electrolytes include those of a copper salt to facilitate a chemical reaction that detaches copper and patches it on the electrode requiring plating. The electrolyte bath should contain three essential inorganic components: copper sulfate, sulfuric acid, and chloride ions. The copper sulfate improves the electrolyte bath’s conductivity since it’s a charge carrier and the copper sulfate acts as a copper ions source.
The chloride ions help minimize plating in specific parts since it combines with organic substances to form a complex solution. You might also want to regulate the copper plating pace by adding a few additives: suppressors, accelerators, and levers. Remember, the plating may not be uniform in every part of the metal, and it helps to have control of the rates using these additives. Here’s a note about what each of these additives means.
Accelerators – This additive helps with enhanced plating rate and usually forms an electroactive species. You may have to vary the accelerator amount in your electrolyte bath to give your cathode some peak plating, with uniformity and consistency being the key.
Suppressors – Suppressors are wetting agents and combine with chloride ions to prevent plating on specific target areas. Technically, these substances reduce the plating rates in places you don’t need, and you must be more strategic when adding them to the electrolyte bath.
Levelers – These substances usually stabilize current distribution and polarize zones having high densities. They also even out the copper surfaces, ensuring they’re flat and don’t have any defects.
Step 2: Check If the Electrode Is Clean
The electrode needs to be debris-free and devoid of chemicals that may alter the binding of copper ions. This process is the most overlooked or manufacturers may not pay much attention to. However, using a dirty electrode will only compromise results, and the plating quality can be below par. Therefore, it helps to properly clean your electrode by scrubbing it with sandpaper or nitric acid solution. The latter can be more applicable in large-scale plating since it allows massive cleaning and eases the work.
As a metal manufacturer, quality finishing is essential and nitric acid can help you clean your electrodes. However, too much of it can wreak havoc on your electrodes, mainly corroding them, resulting in more rugged surfaces. Therefore, mixing one part of the acid with three parts of water is best to guarantee high-level care cleaning and leave your metals unscathed. Besides, you may need to immerse your electrodes in the solution for a short while, perhaps 20 to 30 seconds. That’ll help remove resistant dirt, leaving your metals tidier for better copper plating.
Step 3: Electroplating
After the preliminaries, the actual work ensues – electroplating. The process is straightforward and requires minimal effort. Therefore, having a power source is necessary to drive in current through the electrodes and the electrolyte. The power source must be massive for large-scale electroplating, and the voltage should be colossal.
The metal dissolved from the anode gets plated on the cathode during the process. The anode receives direct current and oxidizes the electrolyte solution, and the dissolved metal ions (the copper ions) get plated on the cathode. This process takes about 30 minutes, but that should depend on the copper amount or thickness you’d want on your plated metal. You can switch the metals you need to plate once you feel satisfied that it’s achieved your desired consistency.
Step 4: Cleaning and Assessments
Electroplated copper permanently sticks on metals, and you have nothing to worry about it detaching or getting bruised. Therefore, you can clean and assess it to determine whether or not it meets your expectations. And if not, you can still repeat the process. You can use clean water to remove the electrolyte solution before storage.
While removing the copper plated cathode from the electrolyte solution, it’s commendable that you prevent direct contact with your skin since this substance can be corrosive or irritating. For large-scale industrial copper plating, having body protective gear can come in handy since you might be dealing with substantial metal stacks and more significant electrolyte volumes. Once that’s in check, your copper-plated metals will be ready for use.
Types of Copper Electroplating Baths
Numerous things come into play during copper plating to make the process more effective. That includes the voltages, electrodes, and the type of electrolyte bath. For the above process, copper sulfate, an alkali, is commonly used. However, other electrolyte baths exist and include the following.
Alkaline Electrolyte Bath
Alkaline copper baths aren’t so common during copper plating but may be sophisticated and perhaps not so helpful in small-scale operations. It involves using an alkaline copper solution like pyrophosphate copper, which is mildly alkaline. Regardless, alkaline non-cyanide solutions and alkaline cyanide solutions still make the cut. However, remember that these solutions can be somewhat unsafe to handle and need more care when using them on an industrial scale.
Acid copper baths
Acid baths are ideal and more preferred due to their ability to handle massive currents, resulting in thicker copper plating. Besides, they’re cheaper and less complex, hence pretty straightforward to use. Acid copper baths are copper sulfate and copper fluoborate baths, which act as copper reserves for electrolysis. The latter, however, has the edge over every other copper plating electrolyte since they’re soluble and their saturation points come later.
Electroless copper plating
Unlike other copper plating processes, electroless copper plating doesn’t need electricity to dislodge copper ions and patch them on the metals that require a plate. Furthermore, they don’t use electrolytes but chemicals and non-conductive electrodes. This copper plating process is essential for metals with more complex geometries since it reaches virtually every metal surface. Besides, it’s a go-to electrolyte if you fancy uniformity and precision. However, this electrolyte isn’t so commonly used in industrial applications but is a mainstay in the small-scale copper coating.
The Benefits of Copper Plating
For viable reasons, copper plating is widely regarded as an essential metal finishing touch. This process is straightforward and effortless compared to other metal finishing touches, including polishing and color coating. Here are the copper plating benefits you should be aware of as an electroplating manufacturer.
Durability and Flexibility
Copper is highly malleable and doesn’t compromise metals’ structural integrity even when moved at angles. Bending or shaping copper plated metals shouldn’t be challenging, even for thicker plates, since copper is flexible. Even so, bending, twisting, or shaping your metal won’t affect the plating since this metal plating doesn’t come off regardless. That makes your finished metal parts more durable and will serve you for a long time.
Incredible Corrosion Protection
Despite rusting in the harshest conditions, copper offers cover to most metals highly prone to rusting and wear. For instance, copper plating iron boosts durability if it covers the exposed parts from moisture and air. Other metals also relish copper’s protective abilities since it helps create a protective barrier to lengthen metal lifespans.
Copper conducts heat and electricity more proficiently, thus a preferred metal for coating and plating. This metal has been a mainstay in the electronics industry since it gives little heat and current flow resistance compared to most other metals. Therefore, besides protecting metals and preventing corrosion, copper helps improve metal conductivity for metals that don’t measure up.
Improved antibacterial processes
Copper is a widely accepted coating for lab and hospital equipment due to its inherent ability to obliterate germ populations. No single bacteria can survive on copper since the metal kills them, inhibiting their breeding. With copper-plated equipment, you don’t have to go more profoundly into disinfecting your gear since the material does all the work for you.
Copper plating is minimalist regarding the processes, making it more cost-effective for giving metals an aesthetic appeal. Copper is a viable alternative to other more expensive coatings like silver and gold. And although it hardly comes close, copper can replicate this costly plating with an added benefit. Copper can conduct electricity and heat, giving metals a boost the same. Besides, this metal doesn’t quickly wear off and is incredibly durable, hence an ideal option for the costs.
Copper plating is an essential metal finishing process with a pretty straightforward process. And while it may involve using electric current and electrolytes, it’s not always the case since chemicals, and non-conductive electrodes come into play during electroless processes. Copper plating is a cost-effective process and accrues metal manufacturers numerous benefits, including metal flexibility and antibacterial properties. Hopefully, this article will shed some light on the four copper plating steps to help you improve your copper plating process.