Miniaturized High-Reliability Interconnects Fuel Medical Device Advancements
Smaller medical devices need miniaturized interconnects to achieve greater functionality and portability in medical diagnostic, monitoring, and surgical equipment.
Patients want home-based monitoring, fewer clinic visits, lower costs, and shorter hospital stays. Physicians want more precise data and mobile care for difficult to reach or underserved regions. These trends have driven demand for compact, portable monitoring equipment that travels with the patient and communicates critical data to physicians via the cloud. To serve these intentions, highly reliable portable equipment with powerful processing capabilities is being developed. Every element of the equipment design is a candidate for miniaturization.
Fortunately, early models for the evolution of miniature electronics arose from other industry challenges. In the consumer market, small computing products, including wearables, contain high performing chip technology. In the telecom and the petroleum industries, portable test equipment conducts diagnostic functions, while providing reliability and ruggedness for field applications. GPS modules, missile guidance systems, and portable military equipment also pushed the electronics industry to innovate miniaturized solutions. One important answer emerged with the C-MOS (Complementary Metal-Oxide-Semiconductor) chip technology. C-MOS techniques have allowed significant increases in function and processing capacity while simultaneously improving the density, reducing size and weight, and contributing to the ruggedization of portable electronic products — an important consideration for medical devices that are used in busy clinical settings or home environments.
Among the pioneers of medical miniaturization, pacemaker manufacturers such as Medtronic and Boston Scientific used C-MOS technology to combine analog and digital signals into a single-chip pacemaker. This reduced size and weight while increasing the analysis and control functions of the device. Soon, the design of digital medical instruments, from stethoscopes to defibrillators, followed chip techniques similar to those used to develop small, lightweight, and powerful military and consumer products. Since then, processing chips, instruments, connectors, probes, and sensors designed into medical equipment have seen an accelerated evolution towards miniaturization.
Silicon chip designers have also evolved to serve miniaturized medical devices, primarily with C-MOS and related technologies. In the past, electronic circuits using analog technology or even earlier digital chips required relatively high voltage and used more electrical current. The instrument boxes began with large power supplies and large wire systems running circuitry within the instrument to feed the electricity-hungry modules inside. Wires had to be large enough to handle the current flow and insulators had to be thick enough to keep circuits from shorting to one another. Cables were designed to handle analog sine-wave signals for long runs and were also shielded to reduce electrical noise inside the instrument.
Today’s mini-medical systems on a chip, however, have changed the rules and electrical demands in the whole instrument. New medical chips do not require the same level of support and protection; the signals are predominately digital. Voltages are usually regulated from 12 volts down to as low as 3 volts. Current flows have dropped from nearly 3 amperes to ranging in the 100 mill-amp range and lower. Power supplies or batteries are dramatically smaller and lighter than in the past. Interconnection systems within the instruments can be significantly reduced in size. In addition, wiring can be nearly half as large with plenty of capacity for current flow. With lower voltages, the insulator materials in circuits can be significantly smaller and more compact. As a result, miniature connectors and smaller wires solve an additional size and reliability problem for medical instruments. High reliability, ruggedness and long life can be achieved if designers use the high reliability standards previously proven in other high-technology applications, such as military and aircraft circuitry.
Cable and connector manufacturers have developed micro-miniature and nano-miniature connectors specifically for the medical industry. Using wiring made up of 30 AWG conductors (approximately .012 thousands of an inch in diameter), cables have become more flexible and can hold more signals in smaller and lighter interconnection systems. The mating connector designs have reduced sizes from the older 100 mil. size connectors, often used in household computer towers, down to the miniaturized connector systems at .050” (1.3 mm) and .025” (.625 mm) spacing.
These miniature connectors can handle increased chip function in about one-fourth the space of previous systems using smaller wiring systems. Portable devices can use chips right at the probe tip and be connected by miniature cable to the monitoring instrument. They can be easily disconnected for cleaning or disposal using miniature in-line connectors designed specifically for the instrument.
Miniaturized connectors in medical instruments must meet stringent quality and reliability standards. The spring pin and socket system has proven reliability over wide ranges of shock, vibration, and thermal changes. Made of BeCu (beryllium copper) with high tensile strength (17,200ksi), this format withstands the use and abuse equipment endures in fast-paced medical settings. Pin and socket elements selected should also pass plating tests specified in Mil. B488-type II, Code C class 1.27. This requires a strong nickel plate barrier that is coated with 50 micro-inches of gold. When placed into miniature insulator housings molded from LCP (liquid crystal polymer), the connector tests at the highest level of reliability.
Additional features that reinforce this assembly include Teflon-insulated wiring that is carefully laser stripped to avoid nicking the miniature wiring inside. This is then crimped into the back section of the pin system. The pin-and-wire set are fixed into place within the LCP insulator with epoxy. An over-molded shell that can be customized to the designer’s criteria completes the assembly. Alternately, the pin-and-wire set are inserted into a metal housing to finalize the miniature medical connector. This high-reliability assembly method is sometimes called “crimp-and-poke” technology. Benefits of this assembly process are precision, tight tolerances, and high-quality miniaturization that greatly exceed the performance of single spade pins in lower quality plastic housings.
Materials selection is another important factor that differentiates medical grade components from those used in consumer products. Materials that resist bacteria growth are essential. Materials must be sterilizable through a variety of rigorous processes without damage to the integrity of the design.
Micro-miniature and nano-miniature connectors should be selected in the early design stages. Solid model designs can be used to adjust shells and insulators to fit into handles, probes, or custom mounted into instruments. An additional benefit of the solid model design interface is that it is quick and shortens prototype cycles. Consult with your connector supplier for assistance to determine the best configurations for the instrument design and for the modular assembly process. Today’s miniaturized interconnect systems are smaller than ever while offering more powerful, reliable options for the needs of modern medicine.
Bob Stanton retired from Omnetics Connector Corporation in 2022. He continues to contribute to the connector industry as a mentor for young engineers.
For more information on miniaturized medical interconnects, visit Omnetics Connector Corporation.
Like this article? Check out our other articles on high-reliability connectors, our Medical Market Page, and our 2023 and 2022 Article Archive.
- Miniaturized High-Reliability Interconnects Fuel Medical Device Advancements - February 7, 2023
- Nano-Circular Connectors for Sensor Designs in Rugged Applications - March 22, 2022
- Miniature Connectors Empower Military Robotics - September 28, 2021