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Issues and Answers

Tue, 11/11/2008 - 11:37am

Issues and Answers

Compliance and compatibility are critical factors in the design of medical electronics equipment. The following are responses to questions posed by ECN regarding how vendors address certification issues and what types of testing are required.

Q.  How do designers work with vendors to ensure components will meet certification requirements for use in medical devices?  If a component does not have medical certification, how can vendors and designers work to obtain that certification or is it easier to find an already-certified equivalent device?

John Kruse, Medical Applications Specialist, Analog Devices

A. Most components do not need special medical certification. Typically, components are certified for medical use during the qualification testing of the medical device in which they are used. Components that cross the isolation barrier, such as Analog Devices’ digital isolator products, comprise the largest category of parts that do require certification.

IEC60601-1 Edition 3 has raised the bar for medical design engineers because it requires them to assess their design for risk per ISO14971 as well as for essential performance. Edition 3 is being enforced in different timetables around the world. To meet the requirements of Edition 3, the design engineer needs to include additional data on specific components in their design, such as failure mechanisms and reliability data. The design engineer must work with an IC vendor to acquire this data. In addition, the design engineer will want to limit his/her component selection to parts that have well-written specifications that contain minimum and maximum specifications for critical parameters. To streamline the design process for medical design engineers, Analog Devices makes reliability data for its products available on the company's website.

Medical devices, particularly those utilized for life sustaining applications, require the highest level of reliability where latent component failures cannot be tolerated. Medical performance specifications are designed and written for the maximum property ratings of the individual product associated with the specification. Flow down of specifications to the component supplier is done using a source control drawing, which initially can be conceptual and may include a formal statement of work. 

To meet the medical designer’s requirements, high-reliability components are designed, qualified, and screened against the highest levels of established components specifications by utilizing extended life testing of multiple lots. Certification of medical devices begins at the component level and can be a grueling task. For example, not only does an implantable device have to be qualified, but also any materials, processes, and sub-components and assemblies must be qualified to critical design requirements. 

Scott Sentz, Director of Marketing, Novacap

A. Medical device design is unique and proprietary to each manufacture. Certification controls are stringently maintained through FDA activities and COTS (commercial off the shelf) alternatives are not permitted. Each and every component must be qualified and certified to device specifications as “medical grade.”

The reliability of electronic components needs to be assessed at the component level, the device level, and for the ultimate reliability in a patient’s application. This includes critical input and output process variables of the component that have an impact from a severity, occurrence, and detection standpoint (the PFMEA approach), and on the future, long-term performance of the component in a patient’s application. Having a bulletproof screening procedure is critical, as well, to ensure that the component’s use (in an application) is in the “life” portion and not the “infantile” portion of the operational curve.  Product is designed for optimum reliability and repeatability, with each manufactured component lot burned in at elevated voltage and temperature to eliminate infantile failures. It also must be 100% electrically inspected to ensure conformance to strict performance criteria.

Critical specifications need to be continually monitored and controlled with various reliability assurance activities. These need to be engrained in the supplier’s medical component control plan where there are no changes to design, materials, process, product, and equipment after formal certification qualification is complete. Each component’s capability extremes need to be determined through elevated and fatigue-type testing against the critical drawing criteria to evaluate thermal, mechanical, environmental, and electrical performance.

Q.  What types of formal compliance testing are necessary or recommended for medical electronics components? What is typically done-in house and what is contracted out?

John Kruse, Medical Applications Specialist, Analog Devices

A. Components that are not designated as critical components in the medical design do not normally need separate, formal compliance testing. They are qualified for use in the medical design, when the medical device undergoes formal certification testing. Digital isolation components, however, need certification from Underwriters Laboratories (UL) and/or Verband der Elektrotechnik, Elektronik und Informationstechnik (VDE) for use in medical products. Both UL and VDE are standards organizations as well as test service providers. Whether a medical device must carry a UL or VDE certification depends on regional requirements.

Compliance testing must be conducted by a certified testing agency, such as UL or Technischer Uberwachungs-Verein (TUV) to obtain the CE mark. In addition, the Canadian Standards Association (CSA) will certify components for use per IEC60601.  The IEC60601 standard can be applied to systems as well as parts. Given this, it is beneficial to have certain parts (such as digital isolators) certified independently so a medical device designer can use them with confidence.

For medical designs developed in the United States, the design and testing procedure also has to meet the quality system regulations of the Federal Drug Administration. Verification and validation testing is usually done in-house by the design house before the medical device is submitted for testing to obtain the CE mark. To receive the CE mark, the medical device has to meet the requirements of IEC60601-1. To further complicate things, many countries have their own version of 60601. 

To navigate the virtual minefield of international medical standards that must be met, most medical companies have medical-standard experts on their staff. Smaller companies can employ consultants that specialize in this area. In addition, test houses and IC manufacturers can answer many of the questions and help the medical design engineer to qualify their design for medical use.

Scott Sentz, Director of Marketing, Novacap

A. Formal compliance testing is driven by the medical device manufacturer.  Electronic component manufactures, including subcontractors for manufacturing and test screening, need to be included in the formal compliance qualification testing. Compliance testing will evaluate the design, materials, process, and screening parameters utilized in component production. 

Multiple, distinct lots need be evaluated to ensure process capability agreement against final test protocol results. Requirements are set individually by each medical device manufacturer that eventually after qualification end up being flowed down into the supplier’s ISO or FDA quality management system. These qualification activities ensure components will be certified against key FDA requirements thus allowing the device to be registered and listed with the FDA.

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