The need to minimize healthcare costs is creating greater demand for medical electronics equipment that, among other things, improves and expands patient diagnostics inside and outside healthcare facilities. For example, portable medical instruments such as glucose meters, blood pressure monitors, and oxygen meters can be designed with communication capabilities to provide continuous information to caregivers almost anywhere. Small handheld devices can also improve various diagnostic procedures in medical offices. While such devices hold the promise of improved care at lower cost, they require advanced technologies that allow greater miniaturization to improve portability and functionality while providing safe usage.
Many of the same considerations apply to medical instruments used in fixed locations or with limited mobility. Larger, more complex instrumentation, such as robotics used in surgery, can benefit from advanced electronic interconnections that make production more efficient and the final product more compact and user friendly. In these applications, larger connectors may be acceptable or even desirable when more wires and other interconnections are needed to control complex computerized functions, while making connections simpler and more reliable.
FDA Approval Issues
Taking a new medical device of any kind through all the steps for FDA approval is a time-consuming process. Therefore, R&D engineers must take all practical steps to shorten the product development cycle and time to market. The latest electronic connector and interface technologies can help achieve these goals. Some ways modern connectors and interfaces can help are:
• Shrinking connector sizes for a given set of functions
• Adding functions to connectors that once required separate circuit components
• Allowing hybrid connectors that carry pow er, communications, control signals, etc.
• Improving safety through better latching methods and electromagnetic interference (EMI) shielding
Data Communication Interfaces
The use of data communications is a feature common to many medical devices as they are linked to healthcare providers wirelessly or by cabled LAN networks. Electronic connectors are essential elements in these connections and must work flawlessly without contributing noise or distortion to the signals.
Often, despite careful system design, EMI and noise can find its way into data lines. Another danger is damage from electrostatic discharge (ESD), which is the transfer of a static high voltage charge from a human body into the electronic system. Often, separate suppression devices are added to data communications interface circuitry for protection, but this adds considerable cost and bulk in the form of components and assembly labor.
Today, subminiature D-sub connectors, the most common digital I/O interface, are available with built-in filtering that minimize these dangers to sensitive medical instruments. They can be purchased with inductive ferrite filtering in the printed circuit board (PCB) material that holds the connector pins, as seen in Figure 1, left. This cost-effective low-level filtering has minimal insertion loss while reducing EMI emissions that might otherwise be close to the specified limit.
Another approach to D-sub filtering is a patented four-layer PCB material with surface mount chip capacitors, as seen in Figure 1, right. As a result of the filtering performance of the capacitors and the screening effect of the PCB, this provides complete protection from any introduction or radiation of noise through the I/O port. In addition, ringing and crosstalk are virtually eliminated.
Filtered D-sub connectors are available in a range of configurations that include standard and custom pin-outs, various housing and hood styles, cable and bulkhead mountings, surface mount types, straight and right angle pins for PCB reflow soldering, etc. Builtin filtering eliminates or reduces the need for separate suppression devices, resulting in smaller, less costly data communications circuit designs. In addition, this style of built-in filtering fits within standard D-sub shells, which allows designers to add filtering late in the design stage if an EMI or ESD glitch is discovered, and may avoid the need to modify a circuit board to suppress these problems.
Another way to shrink medical electronics is with molded interface device (MID) technology. MID, combined with other electronic packaging technologies, such as flexible PCBs and a variety of semiconductor chip mounting techniques, can be used to create medical devices with higher-level functionality and miniaturization.
MIDs are injection molded plastic elements carrying electrical circuits. Their electrical connections can be routed “around corners,” and components can be mounted in various spatial directions. MID incorporates such technologies as active compounds (typically metal complexes) in the plastic moldings, two-shot molding processes, laser direct structuring (LDS), and laser subtractive structuring (LSS) to create connection interfaces and conductor paths. This allows highly miniaturized circuit assemblies with a great deal of complexity, manufactured to precise specifications.
In addition to saving space, this enables direct integration of IC chips and small surface-mount devices (SMDs) into the molded housing. It also allows for the creation of recesses, channels, and openings for sensors, and contact elements. Three different processes are typically used in creating MID assemblies.
Two-shot molding is a two-stage injection molding process using two different plastic compounds, one of which can be metalized to create conductor paths, while the second compound is inert to plating agents. Minimum line widths and spacing are around 400 μm.
LDS uses laser beam to define electrical conductor paths and functional features. The beam selectively activates metal additives in a molded polymer to allow plating of the conductor paths with minimum line widths and spacing down to 150 μm.
In LSS, an entire surface is chemically activated and metalized. The electrical structure is created through laser ablation and subsequent separation of the tracks by etching. Dimensional resolution is about the same as in LDS.
The processes most commonly used in MID assemblies are wire bonding, flip-chip mounting, and attachment with conductive adhesive. MID devices can also be created with connection pads for surface mounting to a circuit board.
In addition to final packages with a reduced height and footprint, circuit components and traces can be easily integrated with I/O connectors to create an assembly that becomes the finished device package. Conductive traces can be created to take on shapes that allow them to function as antennas, heaters, shielding, and switch contacts.
Hybrid connectors are a recent development that allows mixed transmission media, such as power, control signals, data communications, and pneumatic lines in a single connector housing. This eliminates the need for multiple connectors for different purposes, shrinks the overall size of the finished product, and lowers costs. Other features have been added to improve functionality, reliability, and safety.
An example of this new type of connector is used in a laser hair removal instrument created by Lutronic Cor por ation, Fremont, CA, which required FDA approval before being commercialized. The design of this instrument involves a handheld laser wand connected to a table- or floor-mounted power and control unit. One design challenges was to figure out the best way to run power, control signals, and cooling water from the main console to the laser head.
Major design criteria included a streamlined look with compact external connections that would be easy to connect and disconnect the laser head from the console. For Lutronic to develop a custom connector with these features would have required a difficult and lengthy engineering project. Therefore, its engineers looked for an off-the-shelf connector that could be modified to incorporate all the instrument’s electrical/ electronic interface wiring, plus laser head cooling water connections. They found it in HARTING’s Han-Yellock® connector line. (See Figure 2)
In the Han-Yellock connector, a variety of inserts are available to carry power, data communications, signal wiring, and air for cooling or control. In Lutronic’s case, the pneumatic functionality was modified to carry cooling water to the laser head. Based on earlier Lutronic designs of small cooling water connection components, this functionality was a relatively easy addition to the Han-Yellock housing. To avoid the possibility of water leakage into the electrical connections, which wasn’t an issue with a pneumatic insert, Lutronic engineers designed a solid separator wall to isolate the water from the electrical side of the connector.
Along with a mating bulkhead connector on the main console, this hybrid connection carries signals that control the temperature parameters of the laser, communicates the status of laser head control buttons and trigger assembly, and supplies cooling water to prevent the laser from overheating.
It also has a single-hand latching mechanism with audible and visual indicators of the locking status, which ensures a safe, solid connection of the laser headpiece and cable assembly to the console, and makes it easy to swap out laser heads. Another plus is cable production that does not require any special assembly tools, and availability of economical off-the-shelf hardware.
Other Interconnect Considerations
Medical instruments used in healthcare facilities can often mean the difference between life and death. In these situations, cable interfaces must allow fast, foolproof interconnections by doctors and technicians not well versed in electronic technology. In such critical care usage, connector contacts must align easily, provide proper polarization, and have a housing with quick-release latching and robust strain relief for the cable.
In addition to efficient assembly for reduced end product cost, the connector design should provide foolproof shielding and grounding to ensure safe connections. One way this is accomplished is through a design that provides automatic grounding of protected earth (ground) terminals when a completed frame is assembled into a metal housing. In this type of design, the cable shielding can be attached to protected earth terminals to ensure grounding to the connector frame.
Weight and portability requirements continue to be a trend in medical electronics that push the boundaries of extreme component density, without sacrificing the robustness of connector interfaces. These design goals are essential in advanced miniaturization efforts for portable devices. Still, dense electronics and compact size are crucial in many medical devices and systems, not just ones that are portable. The connectors used in instruments for both types of application must have all the characteristics just mentioned, including connectors used inside instruments.
One example is mezzanine connectors used on PCBs for routing a variety of signals and power. Miniature, robust connectors using surface mount technology (SMT), like the one shown in Figure 3, have high contact density that helps maximize space utilization inside instruments. They are available for “board-toboard” and “board-to-cable” applications. In the latter, insulation displacement connectors for ribbon cables provide a high degree of freedom to system designers. These scalable mezzanine connectors provide a robust interface that can absorb considerable mechanical stress on the solder contacts, allowing repeated insertion and removal.
Surgical Robots Push Interconnection Capabilities
Nowhere is the demand for connector sophistication, complexity, and reliability greater than in robotic surgical equipment. The precision, quality, and control required in these systems are extremely high and can be met only through sophisticated interconnections. In addition to high performance features, connector solutions must come in packages with reduced size and weight. These qualities are crucial, as the safety of the patient depends in part on the surgeon’s ability to easily maneuver robotically controlled instruments.
High speed analog and digital signaling is commonly utilized in surgical robotics. The radio frequency (RF) interconnection systems used in these applications have many of the same requirements as the mezzanine connectors mentioned above. Designers must strike a balance between high performance and superior reliability.
Designs like the one shown in Figure 4 can handle high frequencies while simplifying board construction. This type of interconnection design offers high density with the reliability of blind mating features. Because the design also allows ganged connectors for RF, power, and data on the board, this modularity is of great interest to designers concerned with a combination of safety, dense packaging, and easy assembly.
The article was written by Edmund Garstkiewicz, Market and Applications Manager for HARTING North America, Elgin, IL. For more information, Click Here .