‘Checking Up’ on Medical Electronics Print E-mail
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Written by Zulki Khan   
Tuesday, 30 September 2008 19:00

A healthy relationship involves understanding FDA documentation.

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Medical electronics assembly demands a different set of criteria than do commercial PCBs. In particular, the US Food and Drug Administration (FDA) requires specific documentation, especially for verification of certain processes. Complying with FDA-approved documentation is considerably easier when an EMS provider is ISO 13485 certified. The reason: the considerable traceability embedded in the standard.

Beyond FDA documentation, today’s medical electronics assembly also requires special testing, avoiding obsolete components and a detailed evaluation of a Pb-free product, as a looming EU RoHS Directive is expected to include medical electronics.

The FDA is the US’s governing body for approving medical electronics devices intended for monitoring or intervening with the human body. Consequently, FDA approval for work performed by medical electronics OEMs and EMS providers is a tightly controlled process involving precise documentation covering audits, design capability evaluation and verification. Improperly documented, incorrect or incomplete information stemming from design has adverse effects during assembly processes and FDA approvals.

Among other things, an FDA audit includes when design reviews are documented, how comprehensive these reviews were, and the type of a design’s systematic examination, which is performed to evaluate the adequacy of design requirements and changes. The FDA also evaluates a design’s capabilities to identify problems it is intended to resolve. Normally, to meet this objective, medical OEMs perform informal technical reviews within the design team. But these reviews are then followed by more formal technical issue reviews and feedback from non-development design team members.

That’s important, because design and documentation reviews begin with an examination of the development plans. When the FDA looks at the specification and its documentation, it is checking into design specification changes, listed testing plans and procedures, and other associated documentation and activities associated with a given project.

Verification is expected at each step of the different lifecycles of medical changes and implementations. Results validation is then conducted to prove overall efficiency of a medical device. Hence, there are considerable documentation stages and detailed procedures an OEM or EMS provider needs to know. They need to ensure all revision and specification changes are properly documented with dates, specific details and proper signoffs.

Take, for example, a design change involving a slightly higher speed component. In this case, the original component had a 6 ns rise time, which was then changed to 3 ns. It’s best to use the same component manufacturer to maintain similar markings so that the part number shows one or two decal changes and represents a minor change. If the EMS provider is not careful in documenting this change, and this oversight gets through to assembly, the original component will be included on the PCB being assembled. As such, the medical electronics subassembly has a higher probability of failing in the field at those speeds.

This and other subtle changes alter the rev level; therefore, it is imperative to change the documentation’s revision level. A disciplined procedure calls for everyone involved in procurement, design and assembly to be fully aware of and responsible for medical electronics PCB documentation to avoid these problems.

‘The Golden Document’

The documentation control department at an FDA-registered EMS provider releases the official, so-called “golden document” all involved personnel must strictly follow. Document control is an integral part of the Quality System Regulation outlined in FDA Quality System Registration 820.

Section 820, sub chapter H, calls for medical device manufacturers to establish and maintain procedures that control documents. It also mandates designating one or more individuals to review and approve documents prior to issuance. Records of changes to documents are to be maintained. This includes a description of the change, identification of affected documents, and signature of the approving individual.

Document control is equally critical for ISO-registered medical device manufacturers. ISO 13485 and ISO 9000 require quality procedures that are documented, controlled, and effectively implemented and maintained.

If there are component changes, for example, a first line of contact would be pick-and-place technicians, who refer to the documentation to ensure all changes are correctly implemented. In this regard, a reputable EMS provider has its own set of checks and balances in its process control systems, flowcharts, procedures and processes to guarantee documented instructions are followed at assembly.

For example, Figure 1 shows how a project is started from the standpoint of an OEM’s requirements. It also shows how those requirements are met through a medical electronics assembly process. Eight or more major steps are involved. Within each step are one to 10 operations. By implementing this high-level flow chart, medical electronics OEMs are assured critical assembly operations conform to IPC Class III workmanship standards.


Quality control plays a vital role and is the ultimate gatekeeper for detecting every nonconformity in assembling a medical electronics PCB, and before delivering it to the OEM customer. This is particularly true for uncovering minor component or design changes, which can be overlooked easily, eventually resulting in RMAs.

An FDA documents review also includes validation coverage. When validating a process based on design changes, it wants to see how complex design changes are and what the associated safety net is. The FDA wants to know what those safety procedures are and how they are evaluated in terms of validation coverage.

Also, the FDA wants to know the level of independent review those changes have undergone. For instance, did those changes go through an internal technical committee or did feedback come from non-development team members? On the other hand, if self-validation is performed, it will then be difficult to defend those changes during an audit.

The FDA performs hazard analysis as part of a documentation review. It seeks the hazard mitigation techniques detailed in the documentation and how a product’s residual risk is described and justified. It wants to know the residual risks designed into design changes for a specific product. The probability of a problem may not be initially apparent. But after a medical electronics product has been in use for a year or two, the FDA wants to know of any residual risk of that product failing.

Special Testing

Testing is specialized for medical electronics because different devices have different testing requirements. Test challenges are long and varied largely due to overwhelmingly complex FDA regulations. As a result, the demand for verification and validation is exceedingly high, and its traceability extremely critical.

Figure 2 shows special testing requiring custom test fixtures. Here, product testing is for fluid viscosity applications. But in most instances, test requirements may be so challenging that a medical electronics OEM has no option other than to rely on outside test vendors. For example, special testing is needed for capturing such radiation devices as “x radiation test”; most EMS providers lack this kind of testing capability. Therefore, special testing pays handsome dividends because it plays an important part in increasing quality and reliability standards, minimizing warranty costs and testing specific applications.

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Complying with ISO 10993-l is a case in point for special testing. It was adopted by the European Union in 1993 and amended in 2007, and any medical product marketed and sold there must be qualified to it. This standard describes general principles governing biological evaluation of medical devices; device categorization based on the nature and duration of contact with the human body and its fluids, and selection of appropriate tests. Hence, testing requirements are very specific.

RF designs for small transmitters or medical telemetry devices worn by hospital patients also require special testing. These miniature products transfer patient data from one point to another remote sensing station. Since RF is becoming a major part of medical electronics technology, what’s emerging is specific RF testing, in addition to regular ICT, functional and flying probe.

At times, an RF board cannot be probe-tested because of necessary EMI/RFI shields that limit the flying probe’s movement. As a result, an EMS provider has to rely on functional test because RF is peculiar in nature. Testing has to tune into different frequency levels at different speeds. Functional testing must be thorough and complete as a result.

Obsolete Components

Medical electronics OEMs are at times reluctant to make product changes simply because there’s no reason for them. The product is functioning properly; it is FDA-approved, and everything is time tested and verified. However, components often become obsolete. (This is certainly the case as component manufacturers quickly transition to Pb-free to comply with EU’s RoHS Directive.) As a result, once plentiful SnPb components are either obsolete or difficult to find, and cost a premium. An EMS provider savvy about medical electronics assembly can assist in finding other components that can replace obsolete ones, SnPb or Pb-free, perfectly.

An EMS provider can avoid major OEM surprises by maintaining periodic alerts warning a component’s life is coming to an end, for example. At the same time, the OEM can be counseled on tradeoffs and options. For instance, the OEM can either design out a particular component and test new prototypes. Or, it can (try to) buy sufficient inventory of soon-to-be obsolete components to cover production for years to come. The key is to rely on a knowledgeable EMS provider. The main service here is disciplined communications to keep the OEM updated on obsolete component schedules.

There are three basic guidelines for helping OEMs avoid product catastrophes related to obsolete or hard-to-get parts (Table 1). First is timing. This demands a sound working relationship between component supplier and EMS provider. Communication between these two is critical because a particular design is based on assumptions a specific component will be available over the long run. In some cases, if demand for that component doesn’t materialize, the component vendor may ease it out of production. If that happens, it is imperative the component vendor and EMS provider settle on the right substitute. A close working relationship could mean advance notification of such component changes or substitutions, saving time and expenses later.

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Second, major component price changes at times, in effect, put a component out of reach. Price increases occur for any number of reasons and subsequently, pricing structure changes. Component manufacturers should provide EMS providers advance notice that for the ensuing three months, for example, they are going to do whatever they can to sustain certain pricing levels. But, by a certain given date, component pricing is expected to increase by a certain percentage, for example.

Third is dubious vendors. A small, underfunded supplier may suddenly cease production. In cases like this, it is vital to have sound EMS provider design and assembly support to make this issue transparent to an OEM. If one supplier is no longer available, others with similar components must be so the OEM’s PCB assembly does not miss a beat.

New RoHS Rules

EU’s latest RoHS Directive addendum is expected to include medical electronics. Some OEMs are well en route to understanding the various assembly changes involved with Pb-free. But for those who waited, the road to Pb-free assembly may be bumpy and costly.

As stated, one issue deals with component manufacturers all but ending SnPb production in favor of Pb-free versions. For the reluctant medical electronics OEM, this means hastily engineered, expensive and time-consuming re-spins with Pb-free components and boards. Other assembly-related areas of concern include PCB materials and surface finishes, solder joint reliability, incorrect thermal profiles, hybrid lead and Pb-free assemblies, and using separate PCB design layout, fabrication and assembly contractors.

SnPb materials don’t necessarily translate to Pb-free. For example, using materials like FR-4 with an inappropriate Tg for Pb-free assemblies can severely damage the PCBs, as the Pb-free reflow temperature profile ranges up to 255°-260°C, much higher than SnPb’s peak of 230°-235°C (Figure 3). Also, board surface finishes must be able to withstand these higher reflow temperatures. Pb-free finishes include electroless nickel immersion gold (ENIG), immersion silver, immersion tin, organic solderability protectants (OSP) and a special Pb-free brand of hot-air solder leveling (HASL).

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Solder joint and assembly reliability are achieved during assembly if trained manufacturing engineers carefully implement several process requirements. A number of variables must be considered. Included are alloy melting temperature, an alloy’s wetting characteristics, surface tension properties, solder balling and bridging, cosmetic effects of flux at higher reflow temperature and several others.

Applying a wrong thermal profile without carefully considering PCB materials, surface finishes or the correct Pb-free solder can have catastrophic effects during assembly. Care also must be taken to correctly implement leaded and Pb-free components on hybrid assemblies.

Ed.: For more on Pb-free surface finishes, see Better Manufacturing, pg. 20.

Zulki Khan is president and founder of NexLogic Technologies Inc. (nexlogic.com); This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

Last Updated on Thursday, 25 September 2008 08:35
 

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