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The Right Connectors Help Medical Equipment
Designers Satisfy Demanding Applications
Modern electronic connector and interface technologies can help shrink portable medical devices, and improve the
functionality and cost structure of stationary instruments.
Introduction
Data Communication Interfaces
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 hand-held devices can also improve
various diagnostic procedures in dentistry and 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.
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.
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.
Often, despite careful system design, electromagnetic interference 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
to protect it from these dangers. This adds considerable cost and bulk in
the form of components and assembly labor.
Today, 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
(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.
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 too.
Some ways modern connectors and interfaces can help do this is by:
■■ Shrinking connector sizes for a given set of functions
■■ Adding functions to connectors that once required separate
circuit components
■■ Allowing hybrid connectors that carry power, communications,
control signals, etc.
■■ Improving safety through better latching methods and EMI shielding
Figure 1. D-sub connectors with built-in filtering: Left, inductive ferrite;
right, capacitive filtering.
HARTING, Inc. of North America | 1370 Bowes Rd. | Elgin, IL 60123 | + 1 (877) 741-1500 | more.info@HARTING.com | HARTING-usa.com
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Another approach to D-sub filtering used by HARTING is a patented 4-layer
PCB material with surface mount chip capacitors (Figure 1, right). As a
result of the filtering performance of the capacitors and the screening
effect of the PCB, this solution 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 wide 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 re-flow soldering, etc. Built-in filtering eliminates
or reduces the need for separate suppression devices, resulting in
smaller less costly data communication circuit board designs. In addition,
this style of built in filtering fits within standard D-sub shells, allowing
designers the flexibility to add filtering late in the design stage if an EMI
or ESD glitch is discovered. That may avoid the need to modify a circuit
board to suppress these problems.
Figure 2. MID usage example – Left: Dental decay diagnostic tool. Right: 3D
switch and other MID technology helped reduce the assembly time of this
hand-held laser device from 5½ minutes to 20 seconds.
Injection molding process using special
material
MID Technology
Surface activation by laser
Another way to shrink medical electronics is through 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 higherlevel functionality and miniaturization. For example, electronic circuitry
can become more of a three dimensional (3D) structure that conforms to
an end product shape required for a specific application (Figure 1).
MIDs are injection molded plastic elements carrying electrical circuits,
resulting in a kind of 3D PCB (Figure 2). Their electrical connections
can be routed “around corners”, and components can be mounted in
various spatial directions. MID incorporates technologies such as active
compounds (typically metal complexes) in the plastic moldings, 2-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, MID production processes enable direct
integration of IC chips and small surface-mount devices (SMDs) into the
molded housing. MID also allows the creation of recesses, channels and
openings for sensors, contact elements, etc. using, for example, LDS
(Figure 3). This geometrical flexibility enables interfacing features that
facilitate the next level of packaging steps. Thus, MID technology enables
highly cost effective production.
Three different processes are typically used in creating MID assemblies:
2-shot Molding – This 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 400μm. Although design
changes require tooling changes, assemblies created with 2-shot molding
are very economical in high volumes.
Laser Subtractive Structuring – 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; i.e., a
subtractive process. Dimensional resolution is about the same as in LDS.
Cleaning
Electroless copper plating
Electroless nickel plating
Surface finish by a flash of gold
Figure 3. Representation of a typical MID laser direct structuring process.
The techniques for mounting and connecting IC chips and SMDs are well
documented in electronic manufacturing literature. 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 subsequent mounting to a PCB using
SMD connection techniques.
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 that are more than just wiring – they can take on
shapes that allow them to function as antennas, heaters, shielding, and
switch contacts.
Hybrid Connectors
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, and thereby shrinks
the overall size of the finished product, as well as lowering the cost due
to assembly efficiencies. At the same time, by taking a fresh approach
to connector design, other features have been added that improve
functionality, reliability and safety.
HARTING, Inc. of North America | 1370 Bowes Rd. | Elgin, IL 60123 | + 1 (877) 741-1500 | more.info@HARTING.com | HARTING-usa.com
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An example of this is a new type of connector is one used in a laser
hair removal instrument, which required FDA approval before being
commercialized. The design of this instrument involves a hand-held laser
wand connected to a table or floor mounted power and control unit. One
of the 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 external connections that are compact, a
clean streamlined look to the connectors, and making it easy for users to
connect and disconnect the laser head from the console. Developing a
custom connector with these features would have required a difficult and
lengthy engineering project. Therefore the engineers looked for an off-theshelf 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.
The basic design of the Han-Yellock® connector is shown in Figure 4.
A variety of inserts are available to carry power, data communications,
signal wiring, and air for cooling or control. In this particular case, the
pneumatic functionality was modified by their engineers to carry cooling
water to the laser head. 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, a
solid separator wall was designed to isolate the water from the electrical
side of the connector.
The modified Han-Yellock® connector had the sleek look and feel, plus
a multitude of functional features that make it attractive in a medical
application. Along with a mating bulkhead connector on the main console,
this hybrid connection carries signals that control the temperature
parameters of the laser, communications on the status of laser head
control buttons and trigger assembly, and supplies cooling water to
prevent overheating of the laser.
The Han-Yellock® design also has a single-hand latching mechanism,
with audible and visual indication of the locking status (yellow button in
Figure 4). This ensures a safe, solid connection of the laser headpiece
and cable assembly to the console, while making it easy to swap out
laser heads. (the latching buttons is also available in an off-white medical
color) Another plus is cable production that does not required any special
assembly tools, and is available with 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 and foolproof interconnections by doctors and technicians
not well versed in electronic technology. In such critical care usage, this
means connector contacts must align easily, provide proper polarization,
and have a housing with positive quick-release latching and robust strain
relief for the cable, all of which are included in the connector design
shown in Figure 4.
Figure 4. Basic design of HARTING’s modular hybrid Han-Yellock®
connector series.
HARTING, Inc. of North America | 1370 Bowes Rd. | Elgin, IL 60123 | + 1 (877) 741-1500 | more.info@HARTING.com | HARTING-usa.com
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In addition to the advantages of assembly efficiency and reduced finished
product cost while ensuring safe connections, are foolproof shielding and
grounding. An example of how this is accomplished is automatic grounding attachment of PE terminals when a completed frame is assembled
into a metal housing (Fig. 4). In this type of design, cable shielding can be
attached to ground 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
mentioned above.
An example would be the mezzanine stackable 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 5,
have high contact density that helps maximize space utilization inside
instruments. They are available for “board-to-board“ and “board-to-cable”
applications. In the latter, insulation displacement (IDC) connectors for
ribbon cables provide a high degree of freedom to system designers.
Some scalable mezzanine connector designs can provide a high level of
robustness alongside the contact density benefits. The HARTING
har-flex® product family includes extra robust SMT flanges that can absorb
considerable mechanical stress on the solder contacts, allowing repeated
insertion and removal.
Figure 5. Example of a compact SMT mezzanine connector for mounting to
a PCB, available with pin counts from 6 to 100.
Surgical Robots Push Interconnection Capabilities
Nowhere is the demand for connector sophistication, complexity and
reliability greater than it is 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 robotic
controlled instruments.
High speed analog signaling is commonly utilized in surgical robotics.
Similar to the mezzanine connectors mentioned above, the balance
between the requirements of high performance and superior reliability
is applicable to many RF interconnection systems. Designs like the one
shown in Figure 6 can handle high frequencies while simplifying board
construction.
Figure 6. Ganged RF board connector concept currently being tested in a
surgical robotics prototype.
This type of interconnection design offers high RF density with the reliability of blind mating features. This form factor allows for not only analog
signals but can be combined with power and data connections as well.
The modularity discussed earlier is of great interest to board designers,
who are tasked with providing a combination of safety, dense packaging,
and easy construction.
HARTING, Inc. of North America | 1370 Bowes Rd. | Elgin, IL 60123 | + 1 (877) 741-1500 | more.info@HARTING.com | HARTING-usa.com
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About the Author
Ed Garstkiewicz is an Industry Segment Manager for HARTING, Inc.
of North America, Elgin, IL. He has over 17 years of experience in the
electronic connector industry, received his Bachelor of Science in
Mechanical engineering from the University of Illinois in Urbana and
an MS in Human Computer Interaction from DePaul University
in Chicago.
HARTING, Inc. of North America | 1370 Bowes Rd. | Elgin, IL 60123 | + 1 (877) 741-1500 | more.info@HARTING.com | HARTING-usa.com