Cleaning Small-Scale Medical Devices via Vapour Degreasing

Author : Elizabeth Norwood, MicroCare

02 September 2023

Figure 1: The compact dimensions of components inside wearable medical devices makes them difficult to clean
Figure 1: The compact dimensions of components inside wearable medical devices makes them difficult to clean

Wearable medical devices with tiny dimensions are revolutionising healthcare by offering patients portability and comfort benefits. However, for electronics manufacturers, these devices pose significant challenges when it comes to cleaning their internal miniaturised PCBs and other electronics components. To ensure that components are free from production contaminants and residue, advanced cleaning methods and fluids are needed.

Medical devices’ constituent electronics need thorough cleaning and drying before going to subsequent manufacturing steps. The production process often leaves behind contaminants (such as fingerprints, dust, flux residues, etc.). If not removed completely, these can affect device performance and lead to inconsistent outcomes or potentially even a catastrophic failure.

The PCBs inside today’s medical wearables are often densely populated to keep these devices smaller, lighter, less invasive and more discrete for patients to wear. Bottom termination components, like land grid arrays or ones in QFN packages, have very tight standoff heights that often trap moisture under them. This makes cleaning and drying miniature, multifaceted PCBs difficult. Therefore, electronics manufacturers need effective cleaning fluids and methods.
Resurgence of vapour degreasing
One PCB cleaning method that is becoming popular again is vapour degreasing. Widely used in the past, environmental concerns meant it fell out of favour in the late 1990s. However, continuous advancements in solvent technology have led to the development of more environmentally-friendly cleaning fluids, thereby renewing interest once again. Basically, vapour degreasing is a closed-loop system having 2 chambers; the boil sump and the rinse sump. The boil sump holds the specially engineered low-boiling, non-flammable cleaning fluid. PCBs and components are immersed and cleaned inside the heated fluid. Once cleaned, they are mechanically transferred to the rinse sump for final rinsing in a purer fluid (or inside the fluid vapours themselves) before drying. As a result, the parts come out clean, dry, spot-free and immediately ready for the next step in the process (whether that is assembly, finishing, sterilising or packaging). The absence of moisture is especially appealing to medical device manufacturers - since it does not harbour bacteria, thus helping reduce risk of bioburden.

Using a vapour degreaser not only ensures effective cleaning, but also improves manufacturing efficiencies. The entire process takes 6-20 minutes and does not require added drying or cool-down steps (saving valuable production time).
Consistency and repeatability
Once set up and evaluated, the cleaning fluid inside the vapour degreaser stays chemically stable for thousands of uses. Modern vapour degreasers require little maintenance and many of the new cleaning fluids involved will not require daily monitoring or acid acceptance testing. This helps ensure that parts cleaning follows any required process validation specifications. 

Figure 2: A vapour degreaser overview
Figure 2: A vapour degreaser overview

Because vapour degreasers come in many sizes, they can accommodate diverse needs. Whether it is small batch work just requiring a table-top version, or mass-produced parts where a machine holding large quantities of cleaning fluid is needed, the results are always stable. PCBs and components are cleaned using the same repeatable process, so equipment additions or updates are rarely needed when new products are introduced to the degreaser, even if they are a distinct size or are made from a different material. 

Documented results for easier validation
Because the vapour degreasing process is consistent, it runs within established constraints which can be easily audited/documented for validation purposes. A complete cleaning record of the batch may be kept, to prove that all the pre-defined steps were undertaken and that the outcome was as expected. In addition, degreaser operation is straightforward (which simplifies worker training) with ample scope for automation. 

Degreasing fluids
Modern vapour degreasing fluids have strong materials compatibility characteristics, making them suitable for delicate PCBs or mixed-material devices. Their low surface tensions and high liquid densities allow them to penetrate complex geometries and clean thoroughly around and under tightly packed PCB-mounted components. Low boiling points reduce energy consumption, leading to a curbing of associated carbon emissions. Older legacy solvents are being replaced by more-environmentally ones based on hydrofluoroolefin (HFO) technology. 

A better approach to medical device cleaning 
In conclusion, as the size of wearable healthcare hardware continues to shrink and its complexity increases, cleaning will become more challenging for electronics manufacturers. Vapour degreasing offers effective and efficient cleaning, while maintaining compatibility with delicate parts and materials. Modern cleaning fluids, formulated to have less environmental impact and be more sustainable, offer an appealing alternative to traditional solvents. OEMs looking to implement vapour degreasing can seek expert advice from specialty degreaser fluid suppliers. These can conduct on-site audits or perform lab tests with sample PCBs/components to ensure cleaning success. Based on the substrate and the contaminants encountered, they will be able to recommend (or even engineer) optimal fluids and processes.

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