What Is Vacuum Plasma?

An Introduction to Vacuum Plasma

Vacuum plasma, also known as low pressure plasma is a process that takes place in a contained vacuum chamber to create an energetic plasma that is highly controllable.

The typical pink and purple glow of a plasma system is usually because air is being used. The characteristic colours of plasma do change depending on what gas and what energy levels are being used.

Creating a whole chamber of plasma is very useful for complex components with geometry and parts that need whole area exposure. Treating a large plastic moulding with a plasma nozzle is likely going to be tricky to get every evenly and consistently, but it’s exactly what happens in vacuum plasma.

What Does Plasma Do?

For more information on what is plasma in general, and what does it do the a material, see our other blogs dedicated to this for more in depth descriptions. But as quick overview, plasma is an energetic gas which is created by applying high voltage to air in most cases. This highly energetic gas interacts with the material surface to give it new chemistry and useful surface energy that’s perfect for liquids to wet the surface as well as improving adhesion of coatings, inks or adhesives.

While we talk about Vacuum Plasma here, this is very similar technology to both corona treatment and atmospheric plasma treatment.

How Does Plasma Work?

The simplest way to understand how Vacuum Plasma works is to take a look at one…

A typical vacuum plasma system will have four common components:

1. Generator (usually built in)
   • The heart and brains of the machine, this is where the control of the plasma takes place which means taking incoming mains power and stepping up the voltage high enough to create a plasma as well as controlling air flow, frequency and handling incoming and outgoing signals.
2. Control Panel
   • In the photo above, the control is a simple HMI which has several options for changing parameters and observing live information, but this can be replaced with external PLC or other control units or integration into a wider production line.
3. Vacuum Plasma Treatment Chamber
   • The working area of the machine, the chamber is where the parts are placed to be treated. Thick walled systems to be able to cope with the pressure being so much lower inside than outside without deflecting or warping. The chamber contains an energy source to create the plasma and some kind of carrier to hold parts. Pictured above is a smaller production machine, but these could be very large, have multiple doors, shelves or other designs to fit with the production environment requirements.
4. Vacuum Pump (below the machine)
   • To get the chamber down to pressure it is connected to a vacuum pump system. This might be a single large pump or a system of pumps depending on the speed and level of vacuum required. They can be expensive parts of the system so it’s important to balance the size of the machine, the process time and the part throughput to make a sensible system.

What Vacuum Plasma Systems Are Available?

The process of creating plasma and controlling it is similar in most machines, while some may be more sophisticated, have greater control or be tailored to suit the part, the systems themselves contain a lot of common components and designs.

Here are some of the common systems available.

Laboratory Vacuum Plasma Treater

Small scale lab system VacuLAB is a great way of treating small components and is most commonly used for individual parts or for process testing such as creating lap shear or peel test coupons for adhesion testing.

The most useful points with the VacuLAB is that they are quick and easy to use and move, keeping parameters simple and being easy enough to place on a desk or bench and move from room to room. Because of this they need very little training or technical knowledge, most people change treatment time only and use the systems as one button start machines.

Standard Series VacuTEC

The Tantec VacuTEC standard series has four main systems that range from the smaller VacuTEC 2020 model up to the large VacuTEC 100100 model.

Each system has fixed tray sizes relating to their name:

System	Number of Trays	Size of Trays (Width x Depth x Height)
VacuTEC 2020	1	20cm x 20cm x 10cm
VacuTEC 5050	2	50cm x 50cm x 10cm
VacuTEC 8080	2	80cm x 80cm x 20cm
VacuTEC 100100	2	100cm x 100cm x 25cm

Standard systems are very useful for customers and offer common spare parts, fast delivery times and well understood systems that can be trialled and seen before buying.

Custom Vacuum Plasma VacuTEC

Tantec VacuTEC series is available as predesigned machines, or they can be custom built to meet specific part sizes and machine specifications so that they fit perfectly into your manufacturing site.

Design options include:

• Chamber size
  • Fitting a part or jig in perfectly minimises excess space which improves cycle time. For parts that don’t fit the standard series, the custom machines can be much bigger in any dimension.
• Number and type of trays
  • Loose trays are sensible for keeping flexibility, but single large spaces or many small spaces might be sensible for different part sizes and volumes. Loose trays are quick and easy but a specific jigged tray might be sensible, or a captive tray might be a smart option for heavier items.
• Number of doors and door automation
  • Through doors to bridge between clean and non-clean areas, or automatic doors to save floor space or operator intervention are popular choices and can mean the chambers integrate with robot loading and unloading.
• Number of vacuum pumps and their location
  • Using the right size pumps for the machine is important, but putting them in the right place might be a key consideration for where the unit is located. Some place pumps on the roof of the machine which saves floor space but makes maintenance trickier, while others keep them separate so they can be isolated for noise and air movement.
• Process gases
  • Most systems don’t use process gases and rely on air for processing which is highly effective, others might have a tailored process or need a process gas that has zero oxygen to avoid surface oxidation. Multiple gases or gas mixtures can be used an digitally controlled.
• Part handling
  • The majority of systems put to work an operator to load, run and unload the machines but they can also be automated with conveyors, robot loading, jig systems or other part movement system. This works especially well if the factory has a part movement system already in place.
• Software and controls
  • Keeping things simple, the user display screen has quick access for changing parameters, saving information and reviewing runs. Many customers are looking for more specific information or control either for full line safety integration, or for part traceability and machine uptime information. Much of this is standard, but can be enhanced to suit specific requirements.
• Electrode type and location
  • Standard electrodes or high power versions, along with side to side treatment or top and bottom are decided at the design stage.

Rotating Vacuum Plasma RotoVAC

While it’s sensible to have a static part in most cases, some components are too small to handle or even place on a tray. Small items such as rubber o-rings can be tumbled and powders and nanomaterials can be placed in a drum to contain and treat safely.

The ability to treat and change the material surface without the need for wet chemistry or the need for purification and rinsing is something still being recognised by manufacturers as new and exciting. The control and precision of these systems, along with the ease of use and fast cycle times means that they can do things that other systems and processes can’t compete with.

Using Vacuum Plasma – Parameters and Considerations

Vacuum Plasma Parameters

Vacuum Plasma can be tuned to work quickly, work slowly and gently, provide higher hits of power or run specific process methods so you get a tailored process. Many of these parameters are factory set and there isn’t a big need to change them, but they’re there is needed!

• Time is the key parameter; expose the parts to more time and the more plasma will be able to do its work. Especially for trial work its sensible to fix all other parameters and change just this to get a feel for how more and less treatment works with your materials.

• Power is usually second on the list of things to investigate and can be the way to increase treatment levels while still keeping time to a minimum which is often critical in high volume manufacturing. With increased power can also come increased temperature which is unlikely to be a problem on a large part, but might be a problem on delicate materials.

• Pressure is usually used as more of a fine tuning parameter, but it can have a big impact. Run at a relatively high pressure and there’s more molecules in the chamber so while there’s more movement available for the plasma, the energy is shared more. Less molecules can give a more reactive plasma but at the cost of time, especially as it can take a lot longer to reach the lower limits of pressure than a high pressure.

• Gases and purge cycles are avoided where possible to keep machine simplicity and cycle time to a minimum, but for a process that needs a gas and a purge cycle to ensure purity you can add them. Having a highly controlled system that can introduce gases at the right time in the right purity creates an environment that meets very critical standards.

• Machine design features including voltage and electrical considerations and chamber shape and electrode type can have an impact on treatment and while not always a parameter, their consideration in designing the machines can be important.

Machine parameters can be monitored and exported to central systems and each parameter is controlled through the PLC to ensure repeatable treatment, with any deviation resulting in a system alarm if required.

Plasma Treatment Differences

The difference between plasma (and other surface treatments) is often subtle, with atmospheric plasma, corona discharge, vacuum plasma and flame treatment all performing in a similar way. There may be some differences on specific materials, but not often.

In reality, the big difference between the systems is simply choosing the right tool for the job. A large and expensive vacuum plasma chamber to treat an extrusion would not make sense, however the same chamber could treat an aerospace part or an automotive interior dashboard very sensibly.

Many customers start their investigations with the idea that bigger is better, and while the large systems are great for those that need them, they are often overkill for others. A small chamber with a fast pump might be much more sensible, or even two machines rather than one to ensure production keeps running in case or emergencies.

Really we assess this on a case by case basis but here’s a quick overview of these points:

• Part size is often step one, with the key question being “Does it fit in the machine?”.

• Volume of manufacturing is usually the second consideration as it dictates how many parts we need to fit and how fast the process needs to go which helps to size vacuum pumps too.

• Part presentation can make a lot of changes to thinking if existing automation or handling is in place. Some customers move products down their line in sets and require an entire set to be treated at once regardless of timing.

• Budget is always an important factor and with machines ranging from £10,000 up to over £500,000 it is important that realistic expectations are discussed.

Vacuum Plasma Health and Safety

Vacuum Plasma is a really nice machine from a health and safety point of view because all the real work takes place within the vacuum chamber which can’t be turned on with the door open.

There are a few things to consider, especially for different machines so here are a few points:

When machines are used with gases, the bottles and what’s coming out of the pump might be something that requires consideration.

Material movement can be hazardous if the handling system is tricky to use or the parts are heavy, but these systems and components are usually understood throughout the factory.

These machines are really very safe because hazards are within the chamber and within the machine itself. Keeping safety interlocks untampered with ensures safe operation.

Vacuum Plasma Running Costs

Plasma chambers can be very cheap to run, with the smaller end of the systems all working from single phase 13A power suppliers. Even the larger systems don’t use a lot of power, usually under 2kW of power.

However, the vacuum pumps have large motors and the larger the pump, the bigger the motor. This often makes the larger systems in particular a little hungrier and more the power supply to a full 3-phase supply.

For more information, read our running costs blog here!

Vacuum Plasma Uses and Industries

Plasma treatment using vacuum systems has been common for a number of years now, but the technology has really jumped forward since early 2000s and with the replacement of flame treatment and chemical treatment the number of systems installed has increased significantly.

Here are some common uses for Vacuum Plasma technology:

• Metal cleaning and treatment is a big user of the technology because the cleaning potential is high and as with treating a complex moulding, the geometry makes little or no difference. Plasma treatment is a powerful cleaner, and requires no consumables but might not be quite as powerful as a wet cleaner on its own. Combining the two but having much reduced cycle times often gives above and beyond the performance either could achieve alone. This is especially good for machined parts covered in fluids.

• Electrical component cleaning and treatment is becoming more and more common, with PCBs, electrical components and populated assemblies being safe and sensible to place within a chamber. Even with a highly populated and complex board, the plasma will clean and enhance the entire assembly, including under components and in miniscule crevices. This creates a perfect surface for wire bonding, potting or conformal coating.

In each of these applications we are usually looking to improve adhesion of something, most commonly a coating, printing inks, glues and sealants or a tape. We usually refer to this as plasma treating, but actually there is also a high degree of plasma cleaning done in the first place on some materials. Plasma treatment can only occur on the clean material surface, so cleaning must take place first to get to the bare material. It’s not easy to spot the difference here so it’s easy to think that both happen on most materials.

Other Vacuum Plasma Considerations

Vacuum Plasma is a wonderful and versatile tool, but it often comes at a cost and for some the fact that the process is batch is a nonstarter. Even with automation, integration and making the system more of a indexing batch process only taking 2-3minutes it can be the wrong tool for the job – the prime example being products such as profiles and extrusions.

But integration and cost aside, these systems are usually considered the top standard for surface treatment and their repeatability, control and ease of use is difficult to find in any other technology.

When we start a project, we look at each material as if it’s never been seen before because in a way, it hasn’t. The material supplier, manufacturing process to make, the age of the material and the storage and handling conditions can all play a big part in the quality of the part we’re evaluating. With this in mind, questions like ‘how long does plasma treatment last?’ and ‘which is better, plasma or corona?’ are often impossible to answer without working on the problem.

In general, plasma treatment lasts minutes to days on oily materials, days to weeks on metals and flexible, but clean materials, and then weeks to months on clean, rigid materials. Would you see any difference in this theory between plasma and corona? Often no, but sometimes it can be very different.

When working with Tantec UK, we offer full lab support and testing so we can put answers to these considerations and others to make sure you get an answer that’s right for you, your process and your material rather than an outdated text book response that doesn’t work for industrial applications.

Other Forms of Low Pressure Plasma

Tantec manufacture systems that predominantly clean and treat materials, but there are a number of technologies that are sometimes different and sometimes just different names for the same thing.

Some examples include:

Plasma Etching – there are specific etching machines, but using plasma etching for surface treatment to improve adhesion is often the same machine as a plasma treater.

Plasma Cleaner – cleaning using a plasma treatment unit is going to happen as the energy in the plasma vaporises contamination from the material. It’s not likely there’s a specific cleaner than won’t treat, or the other way around.

Plasma Asher – Ashing using a plasma machine is the process of turning a contaminant in to ash which is easily blown away or removed. Very similar to plasma cleaning, it may again be a different name for the same process.

Plasma Deposition – Depositing a material such as a metal film is specifically another process, but for some coatings it is possible to use standard plasma treatment to apply.

We find there’s a lot of supplier specific names and ideas for plasma treating and our advice if your unsure is just to speak with us and explain the problem, it’s often quite a quick discussion if you’re looking to do something completely out of the normal treatment systems.

Conclusion

Vacuum Plasma is a really versatile and powerful tool for many applications and finds its way in to lots of industries, treating a wide range of materials and solving a number of problems. It can be expensive for larger systems but there’s normally a system to suit, and where there isn’t there is the availability to use subcontract treatment services offered by Ebble Manufacturing.

Tantec UK are happy to offer atmospheric plasma trials, rental systems which are available to book through our shop site Ebble.shop and contract treatment which has more information here.