Toll processing can benefit specialised processes such as plasma treatments and diffusion bonding
Manufacturers will often turn to toll processing when looking to utilise specialised expertise, advanced processing capabilities, or proprietary technologies without bearing the financial burden of acquiring and maintaining dedicated equipment or facilities
Toll processing is when a manufacturer processes customer-supplied materials or parts for a predetermined fee. The customer maintains ownership of the materials, but the toll provider applies specialised technologies, equipment, and expertise to produce the final component.
Toll processing enables manufacturers in sectors such as medical devices, aerospace, and electronics to significantly enhance the performance, functionality, and market appeal of their products by integrating speciality materials, precision surface treatments, and other processing features. Manufacturers can achieve these benefits without the capital expenditure and operational complexities associated with in-house production.
The result is often an increase in product value, allowing companies to command higher price points in the marketplace. It is also a cost-effective approach, particularly for small or intermittent volumes.
These benefits can be further amplified when manufacturers engage in toll processing directly with the Original Equipment Manufacturer (OEM) of the processing equipment. Despite this approach offering significant value, it is uncommon because most toll processing is performed by independent third parties using equipment purchased from OEMs.
Third-party providers can lack the in-depth knowledge of the equipment's design, capabilities, and operational limits that only the OEM possesses. This specialised expertise enables the OEM to provide greater customisation, optimised process performance, and tighter quality control.
Manufacturers can gain access to engineering resources, equipment modifications, and technical support that third parties cannot offer when working with the OEM. This is particularly important in scenarios involving materials or novel surface modifications where process flexibility and rapid technical responsiveness are essential.
One example includes plasma treatment systems and diffusion bonding services offered by PVA TePla America, headquartered in Corona, CA. The company acts as an OEM and a toll processor for plasma treatment and diffusion bonding technologies.
While the two processes differ in function and application, both provide performance and quality benefits across a variety of high-tech industries. Plasma treatments enhance bonding and adhesion and enable multiple critical surface modifications. Diffusion bonding facilitates the joining of similar or dissimilar metals to achieve superior thermal performance, mechanical strength, and structural integrity.
Due to the distinct requirements, substrates, and material combinations involved, each customer application is inherently unique, and so successful outcomes depend on carefully tailored process development customised to the demands of each use case.
Suraiya Nafis, director of research and development at PVA TePla America, said, “A single recipe or standardised process cannot be universally applied. Each application requires a tailored approach to ensure optimal performance and compatibility.”
Plasma treatments
In manufacturing, plasma treatments are often used to address problems that other methods cannot. Plasma treatments can add value to products by improving the adhesion of dissimilar metals, depositing coatings, cleaning surfaces, applying a protective coating to repel water or biological fluids, or enhancing surface wetability or a functional coating.
Nafis says one of the most common applications of toll processing is plasma treatment to enhance the bonding of chemical adhesives, coatings, and inks to parts.
Adhesion promotion can be achieved by increasing surface free energy through several mechanisms, including precision cleaning, chemically or physically modifying the surface, increasing surface area by roughening, and applying primer coatings. The materials that can benefit from this process include metal to plastic, silicon to glass, polymer-to-polymer interfaces, biological content to microtiter plates, and non-stick materials, such as PTFE.
The net effect is an improvement in bonding, with some cases achieving a 50-fold increase in bond strength. The wide range of materials, chemistries, and application-specific requirements means that a significant portion of PVA TePla's toll processing work involves developing customised processes for each customer.
Nafis said, “Even when multiple customers request a hydrophilic surface [one that attracts water, allowing it to spread rather than bead up], the underlying process cannot be assumed to be identical. A hydrophilic coating that works well on PEEK may not perform the same on PTFE or a polymer due to the distinct surface chemistry of each material. Each material responds differently to plasma, and variations in substrate material, surface energy, and other factors require a customised process to achieve consistent, reliable results.”
When required, PVA TePla can tailor its equipment to meet specific customer needs, making custom modifications to tools, hardware, or system configurations to support specialised applications and performance objectives.
Once the process has been fully developed, all parameters are standardised and controlled. The recipe is locked, and a formal Standard Operating Procedure (SOP) is established to ensure repeatability and consistency.
Nafis said, “While [plasma treatment] tools may come with a standard recipe, we treat that as a starting point. Our team brings significant expertise in customising processes to meet the unique needs of each application."
An example Nafis highlighted was a project focused on improving the adhesion of silicone to printed circuit boards (PCBs). Silicone is typically used as an over-moulding compound to protect electronics from external conditions. However, the complex topography of a PCB means the silicone must bond to several materials, including polymers, metals, alloys, ceramics, and the FR-4 board itself, each with distinct surface chemistries and surface energies.
Without proper adhesion, silicone can delaminate at the edges of the PCB and form small air pockets on and around components, leading to moisture ingress and subsequent corrosion or electrical shorts.
PVA TePla developed a process that deposits a thin-film coating over the entire board to harmonise surface energy to address this challenge. The process begins with a detailed cleaning and surface activation step, followed by the application of an inert chemical primer to establish consistent bonding. This preparation is vital to achieve a strong, durable adhesion of the silicon over-moulding.
In another application, PVA TePla created a specialised process to render polystyrene microtiter and multiwell plates highly hydrophilic, improving liquid coverage and enhancing the adhesion of biomolecules. Water-based solutions bead on the surface instead of spreading due to polystyrene being naturally hydrophobic. The solution involved molecular-level precision cleaning of the substrate, followed by a surface activitaion step to increase surface energy.
Diffusion bonding
Diffusion bonding is a joining method used to achieve a high-purity interface when two similar or dissimilar metals require superior structural integrity. The process involves applying high temperatures and pressure to metals mated together in a hot press to cause the atoms on solid metallic surfaces to intersperse and bond. Toll processing is utilised for diffusion bonding due to the equipment being large, complex, and costly.
Diffusion bonding is increasingly valuable for joining dissimilar metals, enabling engineers to design components and assemblies with the best properties of each metal. For example, one metal offers superior corrosion resistance while the other provides greater strength.
Diffusion bonding also has applications for conformal cooling. The concept involves bonding layers of sheet metal that contain machined channel/microchannel structures to provide a path for heat dissipation. Today, much of the innovation involves aluminium as one or more of the bonded metal layers. Aluminium’s compatibility with diffusion bonding enables the creation of complex cooling channels in high-power electronics, injection moulds, and specialised heat exchangers.
Turnaround
Whether for plasma treatments or diffusion bonding, PVA TePla supports a broad range of customer engagement models. Some clients send large batches of parts once or twice a year, while others may submit only a few parts on an occasional basis. Regular customers operate on a consistent monthly schedule, often reserving tool time in advance and providing a three-month rolling forecast to ensure sufficient capacity and alignment with their ongoing production requirements.
Turnaround times depend on part volume and processing requirements. With nine dedicated plasma system lines, PVA TePla can run up to three distinct jobs in parallel. For projects with tight deadlines, expedited services are available at an additional cost.
Straightforward, well-defined requirements can often be addressed within days, whereas more complex projects that involve testing protocols, validation steps, or equipment customisation can take weeks to months to finalise.
For manufacturers looking to adopt sophisticated technologies without incurring the costs of capital investment, OEM-based toll processing provides a scalable and technically robust solution that supports both immediate project needs and long-term strategic goals.
