Cleaning Challenges for Medical Electronics

Mike Jones, MicroCare Corporation


Reducing challenging production and performance issues with proper post-assembly cleaning of the PCBs and mechanical assemblies.

Figure 1: Ball Grid Array (BGA) here

The market for medical electronics is huge and growing. The astounding capabilities of digital technology and broadband connectivity are “a perfect storm” enabling doctors to diagnose more accurately and offer therapies more precisely than ever before. They also offer labor-saving benefits that are important in these days of tight medical budgets. For example, products and systems that reduce costs and enable patients and families to do more for themselves — collectively called “wellness management” — are exciting new business opportunities. Remote patient monitoring systems can replace the need for expensive hospital stays. Modern electronics clearly can both improve care and reduce costs. Because of these advantages, the global medical electronics market is expected to reach $4.4 billion by 2022, growing more than 5% per annum over the next decade.

With this growth comes the need to ensure these devices work effectively and reliably. But with the increasing use of complex miniature components with ever-tighter tolerances, managingfaults can be problematic. Quality cleaning can make a big difference.

No Room for Error

Companies designing, manufacturing and certifying medical electronics face a host of challenges unfamiliar to the makers of traditional consumer electronics. Consumer electronics (CE) cannot be compared to medical electronics (ME). Consumer electronics are all about “good enough” manufacturing. In contrast, medical device companies value safety, quality and predictability in order to maximize performance and minimize liability. Unexpectedly, many challenging production and performance issues can be minimized with proper post-assembly cleaning of the PCBs and mechanical assemblies used in these systems.

Cleaning is critical for PCB manufacturers as smaller, more densely populated circuit boards become a standard feature in the medical electronic industry. Without it devices will not function as they should and will not stand up to the rigorous regulations put in place bygoverningbodies.

Consumer electronics can be built to some very generalized standards. The most commonly used are promulgated by the Institute of Printed Circuits (IPC) which defines the manner in which PCB assembly should be performed. This may sound rigorous, but for the medical world it’s not nearly good enough.

The processes used in the development and manufacture of medical electronics offer no room for error. This risk-averse strategy drives the need for products to pass tough regulatory requirements because patient safety is always the priority. Therefore, cleaning should be top of the check list for manufacturers.

The benchmark standard for medical devices is provided by the International Electrotechnical Commission (IEC) in a document called IEC 60601-1. This standard is applicable to any “electrical equipment having an applied part or transferring energy to or from the patient or detecting such energy to or from the patient.”

There is also the Food and Drug Administration (FDA) regulation ISO 10993. This standard evaluates devices within a risk management framework to ensure they are safe. Bioburden, pyrogens and sterility are all assessed with this process.

Cleaning is critical to the assurance that medical electronic devices work as they should and meet the standards and regulations we have discussed however, the increasing use of miniature components and complex PCBs make it a challenge.

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Figure 2: Printed Circuit Board (PCB)

Mission-Critical Cleaning Methods

The computing power and functionality of modern medical devices is directly proportional to the processing power of the PCBs within them. That power is the result of smaller, more densely populated PCBs that are hard to clean. Better cleaning enables engineers to specify stronger, more active fluxes which results in better solder joints. Failing solder joints cause a huge percentage of PCB failures so cleaning is key to their success. Problems with ‘cold joints’, insufficient wetting, bridging, and shorts also can be avoided. In short, better cleaning means better PCBs which means better medical electronics.

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Figure 3: Technician inspecting cleaned product

Plus, it’s not just fluxes that companies need to be concerned about. Adhesives, conformal coatings, fingerprint residues, etc. all need to be removed. This variety of contamination makes cleaning complex.

In decades’ past, aqueous cleaning was acceptable as it was cheap and worked with the PCBs of the time. But as electronic devices become smaller and hotter, with intricate shapes and delicate parts, many manufacturers are opting for solvent cleaning because it delivers better cleaning, more consistently, more quickly and at a lower cost.

In previous decades, vapor degreasing was the default cleaning process for most industries. In the 1990s, aqueous cleaning became more popular as a “greener” option. Many young engineers today have never seen a vapor degreaser and are unfamiliar with the thermodynamics involved. When the performance and operations of vapor cleaning are explained the whole process seems like magic, especially when compared to the familiar but large, wet and noisy aqueous cleaning systems with which they are familiar.

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Figure 4: Vapor Degreaser

So here’s the punchline engineers need to realize: advances in solvent technology have changed the game. Innovations are leading to environmentally-acceptable cleaning options that out-perform aqueous cleaners on today’s modern electronics. Modern, nonflammable, environmentally-progressive solvent cleaning can make a substantial and relatively inexpensive enhancement to the performance, reliability and longevity of medical devices. For example, solvents can greatly minimize bioburden issues. Many manufacturers and engineers are discovering that a properly designed and maintained vapor degreaser can be both more effective and more environmentally-friendly than an aqueous-based cleaning system, and lower costs at the same time.

Vapor Degreasing Processes

Vapor degreasing is a closed-loop system that requires two components: a specially designed cleaning machine (which is generically termed a vapor degreaser, even when they’re not cleaning greases) and a specially-designed low-boiling nonflammable solvent.

In terms of the hardware, vapor degreasing systems usually are comprised of a top-loading batch-style cleaning machine composed of two chambers, “the boil sump” and “the rinse sump.” Both chambers are filled with the cleaning fluid. The machines can cost as little as $20,000 or as much as several million, depending upon the size, throughput and special features desired. Interestingly, vapor degreasing systems are highly scalable, and you get the same results from a small machine as a large one — a benefit not always available to aqueous cleaning users.

The low-boiling solvents are used as the cleaning agents. These fluids typically boil at 40˚C, compared to water at 100˚C, which means they use much less electricity to clean. These fluids also have a lower surface tension and lower viscosity than water so they easily clean under even the smallest of parts. Most vapor degreasing fluids also are very heavy and dense — typically 20-40% heavier than water — which aids in dislodging particulate from components. Lastly but most importantly, because the cleaning fluid can be tailored for the application, delicate parts are easily cleaned and dried with very consistent results, which is an important factor for medical electronics.

Operations are simple. In the boil sump, the solvent is heated and the parts are immersed and cleaned in the fluid. Once cleaned, the parts are relocated into the rinse sump for a finally cleaning in fresh, pure, uncontaminated fluid. The heat in the machine also generates vapor that rises inside the machine until it is captured by refrigerated coils that encircle the perimeter of the system. The refrigeration condenses thevaporsback to its liquid state. This pure, clean distillate liquid is channelled in to the rinse chamber which eventually overflows back into the boil sump. This means that every vapor degreaser is inherently a recycling system — a claim no water-cleaning system can make. Properly handled, the solvents never wear out and never need to be replaced.

It is a general rule in cleaning that “you cannot clean if you cannot wet.” Better wetting means better cleaning. The relative ability of a fluid to wet a surface can be measured by “the wetting index.” This combines the relevant chemical characteristics to predict the quality of the cleaning. The wetting index of a typical, modern, nonflammable solvent is 100 or higher. This contrasts sharply with the wetting index for water, which is 14. Better wetting results faster, better, more consistent and easier cleaning, especially when compared to aqueous cleaning.

Critically for medical devices, with vapor degreasing the parts come out clean, dry, spot-free and immediately ready for further processing. Depending on the process requirements, vapor degreasing can handle the most challenging and complex shapes to ensure they are clean.

Solvent Cleaning – a Win-Win Answer

The low viscosity and surface tension ratings of solvents, combined with their volatility also allow them to clean very effectively, even in small crevices and areas that water in aqueous systems cannot easily penetrate. This is especially important for medical device designers, because it means they are not as limited in product design as they may be with aqueous systems. They can be sure that all the surfaces of the finished product will be effectively cleaned, even under tight-stand-off components.

Solvents are inimicable to bacteria, so solvent cleaning ensures a pyrogen-freecleaning environment.This enhances the results of subsequentsterilizationprocedures. Traditional water-based cleaning is, on the other hand, often a significant source of pyrogen contamination. Water is the primary growth medium for bacteria therefore, removing water from the manufacturing process eliminates a major source of bioburden. This is one of the main reasons solvent cleaning is becoming the preferred choice. Solvents are hostile to pyrogens, so vapor degreasing greatly simplifies process control requirements for eliminating bioburden. Since they are inherently hostile to the bacterial growth vapor degreasing offers an easy way to validate bioburden issues in the manufacturing process.

We also must notforgetthat solvent-based cleaning has other benefits including substantially lower energy consumption, a smaller footprint well-suited for use in the cleanrooms, and minimal capital outlay when compared with a water system. 

It is also worthwhile mentioning here that solvent-based cleaning is a simple process with minimal requirements for engineers to oversee on a daily basis to produce clean PCBs. It is also an easy way to ‘touch-up’ the cleaning process at the benchtop.

Today’s solvent cleaners are effective at thoroughly cleaning components and will stand up to regulatory requirements imposed by the medical industry. Formulations are now cleaner, greener, safer and pose less bioburden risks. Importantly, they avoid the expense and global warming impacts of aqueous cleaning technologies as well as the environmental challenges of old-style chlorinated solvents. They can also stand up to the rigorous standards and regulations posed throughout the world.

A well-engineered process can be easily qualified and validated where ever the process is taking place in the world, this inherently reduces the associated costs in the manufacture of medical device components.

Cleanliness is Key

As we have demonstrated, medical electronic devices by their very nature are extremely complex and pose many difficulties to the designer. At the end of the day the proper operation of the device could be a matter of life or death so reliability is of paramount importance.

Solvent cleaning offers a new answer for design engineers. It enables a critical cleaning process that ensures contaminated PCBs are not the cause of any failure, and that better PCBs can be built and deployed, creating new capabilities. Designers and manufacturers should consider using solvent-based vapor degreasing on their new hardware. New advances in solvent technology mean vapor degreasing not only will be the most reliable solution but also the most cost-effective.