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Medical devices

A lack of a standardised medical grade system


To date, electronic components do not have to meet any standards in order to be used in medical devices. Some component manufacturers have "medical grades", but their definition varies from one manufacturer to another.

Real-life conversation with a manufacturer:

"- Hello Sir, I saw that you offer medical grade components, what does that mean?

- They’re the same as the others, but with additional tests.

- Oh really, and what additional tests do you do?

- Well... whatever ones you want..."

Component standards

If you look at a component datasheet, few standards are indicated. And yet, any serious manufacturer uses standards to qualify its processes and/or products. Some of these standards are generic (J-STD-020 to define MSLs for example), some are related to the type of component (CECC 30300 for electrolytic capacitors), and some are related to the application (AEC-Q200 for passive components in the automotive industry).

Of course, not all components comply with all standards, indeed nor is it always easy to know which standards they comply with. Almost all of these standards require component testing. However, these tests do not have to be carried out on all of the parts, which is fortunate because otherwise the cost would be astronomical.

If we take the example of the AEC-Q200 standard, which concerns passive components in the automotive industry, it defines a whole battery of tests to be carried out on components, including electrical measurements before and after stresses in temperature, humidity, vibrations, etc. and the drifts that can be expected. However, this is only a process qualification, i.e. if the component manufacturer does not change his manufacturing process, he does not need to re-qualify the components.

Device reliability

In order to market a medical device, data on its reliability and the impact of a possible failure on the patient must be provided to the certification authorities. 

Generally speaking, the probability of a component failing is never zero. Its impact on the electronics and operation of a piece of equipment is usually taken into account in the system architecture by applying redundancy/dissembling principles.

Not only are the electronics duplicated (redundancy) so that a random failure is not enough to corrupt the functioning of the equipment, but the duplications are not similar (dissimilarity): they are designed by different teams, with different components, with different means so that one single fault cannot corrupt all the redundancies simultaneously. Although this principle is widely used in systems requiring high reliability (aviation, nuclear, etc.), the high level of integration of medical equipment, particularly when it is implantable, does not allow the number of redundancies to be multiplied sufficiently to ensure system reliability. The reliability of the components themselves then becomes the most important factor in determining the device's reliability.

Component reliability
Component reliability

The need for comprehensive information on component reliability is thus becoming important. This means that commercial grade components should not be used. However, the lack of a "medical" grade on components must be compensated for in some other way in order to understand the concept of reliability. The ideal is to start from the needs of the device itself and the descriptions of the various stresses it must be able to withstand and to deduce the resulting stresses on the components.

First difficulty: the stress seen from the component is not the same as that of the device: its temperature may be higher in operation, it may benefit from a housing that protects it from humidity, vibrations may be attenuated or accentuated depending on the mechanical assembly...

The second difficulty is that component reliability data is only available from the oldest manufacturers. For other manufacturers, you will have to ask for that data, and you might need to make several requests before they send it...

Third difficulty: the reliability data for components may come from tests carried out during the qualification of their manufacturing process and it is not unusual to recover data from 10 or 15 years ago. It will then be necessary to carry out tests on the batches received to ensure that any drift in the manufacturing process of the components does not have a significant impact on their reliability.

In exceptional cases, it may even be necessary to discard parts to keep only those components that are as close as possible to the normal characteristics.


FIDES Guide :

Reliability methodology for electronic systems AEC-Q100 (AEC-Q101, AEC-Q200) : Failure mechanism based stress test qualification for integrated circuits (for discrete semiconductors, for passive components)

 Medical Device Directive 93-42-EEC EN 60601-1: General requirements for the basic safety and essential performance of medical devices

Author : Jean Bastid

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