It is often said that cleanliness is next to godliness. It seems appropriate that medical professionals, whose life-sustaining work is closer to “divine” than any other profession, place the most emphasis on cleanliness. This focus extends beyond the constant hand washing when interacting with patients to medical laboratory cleanliness measures meant to avoid contamination creeping into measurements that may result in inaccurate results, analyses, and/or prognoses.
Medical professional employing laboratory cleanliness practices
Cleanliness is not relegated to the usage of medical devices. In fact, avoiding foreign matter, such as ionic contamination, is a major concern during the fabrication and assembly of circuit boards that will be used in medical electronic devices. The importance of this issue is evidenced by its entrenchment in all facets of medical device building and implementation. This includes a number of the most wide-reaching PCBA design and manufacturing regulations for medical devices set forth by the FDA, FCC, ISO, and IEC. Let’s take a look at these with a focus on the pertinent PCB cleanliness standards for medical device electronics.
Standards to Ensure Medical Device Electronics are Clean
Medical device electronics are unique in that many are designed and developed to not only analyze the human body but directly interact or connect with it while doing so. Although swabs, tongue suppressors, and other basically harmless devices do interact with the body, they are categorized as class 1 medical devices due to the low risk of patient injury. Electronic medical devices are more likely to fall under class 2 or class 3 as the risks to patients are significantly higher.
Regardless of classification, all medical device development must adhere to quality control standards as stipulated in ISO 13485. This standard broadly covers all aspects of designing, manufacturing, testing, and monitoring medical devices. This includes specific steps and actions to ensure reliable operation, which depends to a great extent on cleanliness. Another standard, ISO 14971, delves into particular stages and the steps that may pose risks to the medical device development process. As an example, the choice of PCB surface finish may pose a risk of introduction of impurities to your board prior to assembly which may remain throughout the manufacturing process and negatively impact board performance and/or reliability once deployed.
The PCB standard that directly addresses cleanliness for board fabrication is IPC-5704 Cleanliness Requirements for Unpopulated Printed Boards, which covers preventing or removing ionic contamination and other types of unwanted debris. IPC-6012D, which extends to include PCBAs, covers cleanliness as well as all aspects of circuit board manufacturing. For most PCBA applications, the rules and guidelines of these standards are sufficient. However, the requirements for medical device electronics boards are much higher. In fact, for these boards, a cleanliness regimen is crucial and should include validation that sufficient levels of contaminants are removed during the process.
PCB Cleanliness Standards and Regimens for Medical Device Electronics
When it comes to PCB cleanliness standards for medical device electronics there is almost universal agreement on two points.
1. The need for post-assembly cleaning of circuit boards is “critical” to ensure that medical electronic devices function properly and meet regulatory requirements for reliability.
2. A specific standard that directly and comprehensively addresses the cleanliness of PCBAs used in medical device electronics is lacking.
The rapid expansion of the PCBA industry, especially in terms of board complexity and advanced functionality has presented a significant challenge for regulatory bodies to update or create new rules and guidelines that are pertinent. As a result, much of the attention has gone to management and administrative requirements instead of technical specifications. This has allowed the identified issue of the absence of a targeted PCB cleanliness standard to go unaddressed. In its place, a reliance on other assorted standards (such as ISO 10993 Biological evaluation of medical devices — Part 1: Evaluation and testing within a risk management process, which targets biocompatibility and the associated development risks, and IEC 60601, which provides a set of testing regimens to gauge patient safety when using specific medical device electronics) exists along with a number of suggested cleaning methods, as listed below.
Methods for Cleaning Medical Device Electronics PCBAs
- Ultrasonic Cleaners
By far the most highly recommended method of cleaning PCBAs is ultrasonic cleaning. This method utilizes a temperature-controlled process for a set time interval. The effectiveness of this or any method is dependent upon the type of solution used.
- Automatic Washers
Automatic washers are typically aqueous processes where the boards are loaded into baskets, dipped in a solution, and then dried. Although effective, care must be taken as some solutions can be harmful to certain materials.
- Manual Cleaning
Good old elbow grease can also be employed. For small boards with hard-to-reach areas, this method is ineffective; however, some components (microphones, as an example) must be cleaned manually.
Determining the best method for cleaning is one of the most important steps of a good cleaning regimen as shown below.
PCB Cleaning Regimen Steps
Whether determined by you or your CM, which is often the case, following the steps below will produce the best result.
A. Determine likely soils or contaminants
B. Consult surface compatibility studies
C. Select a wash method
D. Determine temperature parameters
E. Determine the cleaning cycle time
F. Determine the rinse solution
G. Determine an appropriate validation method
For help with a validation method, use ASTM F3127-16 Standard Guide for Validating Cleaning Processes Used During the Manufacture of Medical Devices.
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Performing the work that medical professionals routinely do requires that the medical device electronics they use are reliable. Accomplishing this objective is dependent, to a great extent, on the cleanliness of your boards during and after manufacturing. As quality is at the top of our list of criteria, we at Tempo Automation employ cleaning as a standard part of our PCBA assembly process. Additionally, we will work to ensure your boards meet your PCB cleanliness standards.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.