In the March and April issues of MDT, Perspectives presented the experiences of industry experts in facing the challenges of miniaturization of medical devices and the components used to make them. Following is the final "chapter" of this offering with this online exclusive version, extending the coverage even further of this obviously very hot topic.

Q: In the effort to make medical devices smaller, what has been the most challenging obstacle you have faced, and how were you able to resolve it?

Gijs Werner,

Gijs Werner

Global I&I Manager, FCI

In the effort to make medical devices smaller, the biggest challenge for connector manufacturers has not been reducing the component's profile, which was already addressed in the consumer and datacom worlds, but in reducing the printed circuit board space required by the component's footprint. Connector manufacturers needed to reduce the pitch while offering higher signal performance at higher density. To solve this problem, FCI adapted proven connector concepts from other industries' solutions.

One answer was removing the interleaving metal shields in backplane connectors. The revolutionary system uses edge-coupling technology and an air dielectric between adjacent conductors to deliver high signal density with low insertion loss and low crosstalk, all without the use of costly and space-consuming metal shields. Data rates can scale from 2.5 Gb/s to beyond 12 Gb/s without requiring redesign of a basic platform. Removing the shields offers another advantage appealing to the market: signal connectors can be scaled by varying the number of columns of contacts, the number of contacts per column, and the column spacing. This allows for mixed pin assignments (differential or single-ended signals or power) to provide additional flexibility to system designers.

Another solution was in the development of board-to-board, high-density mezzanine connectors. FCI developed multiple-row, BGA connectors that offer reliable dual-beam contacts supporting signal performance. Expanding the proven connector family with versions up to 528 positions per connector met the needs of the medical industry, especially for medical imaging applications. For medical equipment with very low profiles or dense packaging requirements, these mezzanine connectors are being used on a flex foil; flex-to-board connections fit the tight spaces in many medical applications.

Jan Sumerel, Ph.D.

Jan Sumerel, Ph.D.

Manager of Biomedical Sciences, FUJIFILM Dimatix Inc.

Biological monitoring and medical devices generally have two material components—a biological material that works as both a biochemical reactive site and reaction beacon followed by an optical, piezoelectric, or electronic material signal amplifier that allows a measurable reaction readout. One critical parameter for biodevice miniaturization is the demand for smaller feature sizes at each stage.

FUJIFILM Dimatix, a leading developer and manufacturer of piezoelectric drop on demand printheads, has produced the first ever, one picoliter drop size printhead for functional fluid deposition applications. This capability is enabling feature sizes down to 20 µm. Our ability to decrease droplet size is attained using silicon based MEMS technology.

Drop volumes of one picoliter are important to new material development where the use of nanoparticle-based materials is prevalent due to its inherent properties of increase functionality in a smaller footprint.

As a companion to the printhead, Dimatix has also produced a low-cost, R&D ink jet benchtop printer that allows scientists to easily conduct fluid and process related experiments. "Just push print"—the most common command for the printer—enables an additive, not subtractive, process that precisely deposits metered quantities of fluid onto a variety of substrates including glass, silicon, plastics, organic thinfilms, and metals.

As feature sizes continue to decrease, the need for compatible and scalable manufacturing practices for individual process steps becomes essential. Typically, manufacturing protocols are distinct for each step, but drop-on-demand ink jet printing can be used for the deposition of both biochemical signaling materials and electronic materials. Combining these two components may be critical to biodevice miniaturization. The use of electronic file pattern formation facilitates process alignment. For this reason, drop-on-demand ink jet printing—a simple fabrication process—has become prominent in materials processing for biodevice components and its use is expected to experience considerable growth.

Tom Kannally,

Tom Kannally

Medical Industry Manager, Hypertronics Corp

Industry research indicates that the medical device marketplace is following two trends: product miniaturization and product integration. To meet these needs, Hypertronics has developed a 0.3 mm contact system allowing for miniaturization with greater density for higher input/output within medical equipment such as monitors, therapeutic devices, imaging equipment, and invasive probes. A more efficient use of the system footprint can be realized with a smaller form factor contact/connector system allowing more space for critical functions.

Improvements in portability and patient comfort cannot translate into trade-offs in accuracy and reliability. Moreover, implantable device trends require uncompromised functionality within highly sensitive, highly demanding environments. Accuracy and reliability often need to surpass that of the larger devices they replace. Because of space and weight constraints in these devices, embedded components need to be smaller and weigh less.

Since the scaled-down components still need to perform with the best quality and the highest reliability, new challenges in manufacturing arise. The connectors used in these devices need to be more dense and more compact, and be made out of materials that are best suited for smaller spaces.

These manufacturing hurdles result from:

1. The connector's mechanical geometry: molding, machining, and handling small parts with small features

2. the electrical requirements: smaller distances between electrically charged parts can create challenges in voltage transmission and have an impact on the connector's current carrying capability—driving the potential for compromises in accuracy and reliability.

These manufacturing challenges are overcome with consideration of new materials, more extensive testing, and more accurate molding and machining processes. Connectors featuring smaller components, such as Hypertronics' 0.3 mm contacts, meet the density, size, and weight requirements of the new medical devices coming into the market.

Luke Volpe,

Luke Volpe

Director of Engineering, Metrigraphics Division at Dynamics Research Corp

Extreme Resolution Micro Flex (ERMF) circuits are minute multi-level flexible circuits that carry IC chips and micron sized signal traces. Until recently the typical ERMF was a one or two conductive layer device, approximately 25 mm square with less than ten via holes. These via holes were typically 0.03 to 0.04 mm diameter and were photo-imaged in the polyimide dielectric layer.

As intravenous and arthroscopic sensing, imaging, and repair devices become more sophisticated, the need for smaller, thinner, more flexible ERMF circuits has become more critical. Specifications for this second generation of devices—ERMF2—often include three to six conductive layers with trace and space dimension of 0.005 mm or less and often more than 50 0.02 to 0.03 mm diameter conductive via holes. The three most critical challenges we face in making medical devices smaller are:

1. Reliability of 50 or more via holes with 0.025 mm or less diameters.

2. Achieving minimum acceptable bend radius of 0.25 mm free of trace or dielectric fractures.

3. Minimize trace width while maximizing conductance.

To resolve each one of these issues, we tested and confirmed technological processes that addressed each challenge. We determined that reliability of 50 or more via holes with 0.025 mm or less diameters could be achieved by conducting a series of via hole drilling tests using Yag, CO2, and eximer laser systems. The results showed a dramatic improvement in hole size consistency over the photo-imaged vias. Well-formed laser drilled holes as small as 0.02 mm diameter showed reliable conductance after metalization for arrays up to and greater than 500 densely packed holes.

Since the ERMF process is based on cast liquid polyamide, layer thickness is relatively easy to modify and control. By reducing base layer thickness range to 0.012 to 0.015 mm and the inter-layer range to 0.007 to 0.012 mm, the minimum acceptable required bend radius of 0.25 mm was readily maintained for the ERMF2 devices.

To minimize trace width while maximizing conductance, we maximized trace thickness to width aspect ratio. The ERMF circuit process is based on an additive (electrochemical metal deposition) technology. Typically, a photoresist mold is formed over a conductive seed metal that has been sputter deposited onto a polyimide base layer. The imaged voids in the photoresist (the trace images) are then filled with an electrochemicaly deposited conductive metal. It is the high aspect ratio photoresist image that allows the formation of high aspect ratio, and very rectangular, trace cross-sections. It is the maximized rectangular cross section that allows maximum conductance for any given trace and space dimension.

Nick Koop,

Nick Koop

Manager of Technology, Minco

Continual shrinking of medical device package size creates demand for high density interconnect (HDI) flex circuits. It is important to understand how an HDI circuit can impact manufacturing processes for a fabricator, and whether it fits within the manufacturer's core capability. HDI manufacturing begins when circuit pitch (trace-to-trace centers) fall below 200 µ and via sizes are less than 250 µ. A feature introduced by HDI construction is the microvia. Unlike a traditional plated-through-hole (PTH) that is drilled into the entire circuit stack and plated, a microvia interconnects two single layers within a multilayer stack. This allows use of the entire space over and under this connection within the rest of the layers.

Economical mechanical drilling processes typically form PTHs. The small microvia size does not lend itself to this method. There might be a two-layer inner core that can be mechanically drilled, but subsequent layers usually must be sequentially built up one layer at a time. Each step requires via formation and interconnect metallization. Fabricators have devised many methods to create microvia features. Most common is the creation of a small hole by plasma etching, by laser drilling, and then plating copper between the layers, or by filling the hole with a conductive paste to achieve interconnection. As circuit density has increased, the number of vias required grows even faster. The most practical way to achieve the smallest vias is by laser drilling. New generations of lasers are designed for high-speed creation of these vias in thin substrates. The latest plating equipment is designed to handle these thin materials while providing the high-reliability connections.

Medical packages place high reliability at the top of their requirements. HDI technology is now commonplace in medical circuits, but the feature sizes are not pushing the state-of-the-art limits. Medical devices need to use processes well within the statistical limits of control to ensure the product can be designed for reliability rather than depending entirely on inspection.

Simon Pata,

Simon Pata

Product Line Manager, Portescap, a Danaher Motion Co.

Over the last couple of years, Portescap has been challenged to build smaller motors in an effort to make medical devices smaller. The last challenge that my engineering team faced was to drastically shrink the size of the motor used for CPAP (constant positive air pressure) respirator.

CPAP respirators are used by people having difficulty breathing, but who are mobile and still otherwise able to live a normal life. No need to say that the size of the respirator they carry with them is critical.

Thanks to more than 40 years of multi-technology expertise (brushless, disc magnet stepper), the Portescap engineering team came up with a unique brushless slotless flat motor design (1.260 in. diameter for less than 0.5-inch. length., 26 grams only). We focused not only on the motor size but also on its efficiency, allowing the respirator manufacturer to use smaller battery packs while further shrinking the size of the respirator.

Today our new nuvoDisc motor is 75% shorter and 90% lighter than typical cylindrical brushless motors, allowing CPAP respirators to be about 1/3 the size of a shoe box.

Jim Heckman,

Jim Heckman

Technical Consultant, Standard Register

For medical device manufacturers, safety labels have never been more important. Inadequate warnings could have a wide variety of consequences for the manufacturer as well as its employees, customers, and patients—consequences that range from failure to warn lawsuits to minor injuries or even death.

We are living in a multi-lingual society. In regards to the miniaturization of medical devices, it would be impossible to include every language. A typical ANSI Z535.3 designed safety label would be English only. It would be cost prohibitive to the manufacturer to translate the verbiage into every language. To address the needs of the manufacturer to protect themselves against product liability lawsuits, we suggest going to pictorial-only safety labels. The advantage of pictorial-only is a clear concise message conveyed through the use of pictorials over much less surface area on the device. The first pictorial would include an image of what the hazard is. The second pictorial would show how to avoid the hazard.

Pictures are the universal language when it comes to communications, no matter a person's native tongue or literacy level. Fortunately, these language barriers can be readily addressed with the use of pictorials.

There is a wide variety of standardized pictorials available for use, nearly all of which can be referenced through any number of resources. Examples of such resources include:

•ANSI/AAMI/ISO 15223: Medical devices-Symbols to be used with medical device labels, labeling, and information to be supplied

•BS EN 980: Graphical symbols for use in the labeling of medical devices

Use these resources or standards to identify the pictorials best depicting the hazard to be addressed by the safety label as well as pictorials illustrating hazard avoidance—accurately depicting how to avoid the hazard is a key component that is missing in many inappropriately designed safety labels.

Joe Horvath ,

Project Manager, Valtronic Technologies

Smaller, cheaper, and faster. The phrase is still true in the design of medical devices, implanted or not. Putting more functionality in the same amount of space or even smaller spaces and enclosures is an ongoing challenge for medical electronics designers.

Increased functionality is also of paramount importance, as many medical devices are routinely used today that were not practical 25 years ago. To help meet these needs, processing power continually increases along with microcontrollers that integrate the processing function, flash memory, analog inputs and outputs, and real time clocks. This allows the designer to use one IC instead of several. Flash memory allows for the possibility of software upgrades or changes to a control or signal processing algorithm.

As the implanted medical electronic devices become more and more sophisticated, there is an increased need for bidirectional communications with the device. Wireless communications, via either RF or inductive coupling can accomplish this task. Several IC manufacturers now offer ICs to fulfill this need.

To reduce space, chip scale packages have nearly reduced semiconductor package sizes to the dimensions of the die inside. In certain situations, bare die can be used in either flip chip or chip on board applications. Flex and rigid-flex boards can be used to conform to the shape of a housing or to conserve space by folding back on itself, as in a Z fold. If the application demands it, a custom IC can be designed to perform exactly the task needed for the device; the function of several standard ICs can be integrated into one custom IC, reducing the size of the device.

These innovations of today are being designed and manufactured into the medical devices of tomorrow.