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Miniature
Plug Connectors:
Evolving in Concert With a Changing Electronics World
By Lukas Muth, Combicon Product Marketing, Phoenix
Contact GmbH & Co. KG and
Andrew Bogaczyk, Combicon Product Marketing Specialist, Phoenix
Contact U.S.A.
Since the 1960s, most
electronic components, including diodes, transistors, integrated
circuits, and capacitors, have undergone rapid miniaturization.
As a result, electromechanical elements on PCBs have also
miniaturized. This represents a balancing act between
operability, manufacturability, and size, especially for small
plug connectors with centerlines of 2.5mm or smaller. Let’s look
at some of the challenges confronted by miniature plug
connectors for PCBs from the manufacturer’s point of view, and
consider two new concepts for miniature plug connectors.
To assess the operability of a plug connector system, one must
first identify the work steps required during operation. To
start, consider the three work steps of the wiring process:
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Determine
functionality of terminal actuation
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Prepare conductor
and position it at wire entry
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Actuate terminal
To ensure that these steps are
performed safely and efficiently, the terminal must be clearly
designed to support intuitive completion of the steps. Important
information on the various steps—such as length of wire lead to
strip—can typically be found in the terminal’s data sheets.
Identifying Functionality
In the field, experienced mechanics accomplish this task more or
less intuitively. A mechanic must be able to quickly determine
what steps must be taken to connect the conductor. The
identifiable difference between the wire connection and
actuating areas of each terminal point is a design feature that
helps users in this process.
The user should understand immediately how to actuate the
terminal. Generally, a distinction is made between spring-cage,
insulation displacement (known as pierce contact), or screw-type
connection systems. When a screw is tightened or loosened, the
user can clearly see the action from outside. In the design of
the terminal, the assignments between the screws and the poles
should be unambiguous.
In contrast to screw-type terminals, modern spring-cage
technology acts inside the terminal where it is not visible. For
this reason, the actuation of the spring must be visually
apparent from the outside. One way to do this is to use an
easily identifiable color latch that can only be actuated in one
direction. Another way is to use actuating slots where a
screwdriver can be inserted to remove the wire. IDC technology
also acts inside the terminal—and nearly the same design
principles apply here as those described above.
Effective implementation of these design principles simplifies
the work required in the field. For example, the color orange is
used around the world to mark actuating elements on spring-cage
terminals.
Positioning the Conductor at the Wire Entry
The type of connection technology used determines how the
conductor is prepared. The wire is stripped and then fitted with
a ferrule, or it is trimmed. In screw-type terminals, the user
positions the conductor by pushing it against a stopper inside
the terminal. With IDC technology, the non-stripped wire is
positioned using guide grooves or special guide mechanisms. It
is important to establish the terminal contact as soon as the
wire has been positioned.
Depending on the type of connection, users can complete the
contact using one or both hands. For singled-handed operation,
the user actuates the terminal directly with the wire. Push-in
spring technology is actuated with a single hand. The user
pushes the wire against the spring resistance from its position
in front of the spring until the wire is clamped into place.
Screw-type and spring-cage technology requires two-handed
operation. The user must open or close the actuating mechanism
with one hand while holding the wire in position with the other
hand. Depending on the design of the clamping mechanism, it can
be actuated with or without tools.
Another design feature is the tactile response on each terminal.
For example, one can feel the spring as it closes, or the latch
as it stops. These feedback mechanisms tell the user that the
wire is secure in the terminal. The actuating force must remain
the same for the spring and actuating elements in each terminal
family. This provides users with consistent feedback on the
quality of the connection.
Terminal and Actuating Concepts Offer Potential for
Miniaturization
For centerline sizes of 2.5mm and smaller, the
insulation-displacement connection (IDC) and spring-cage
technologies prevail. Miniaturization is difficult with
screw-type connectors
 because
the size of the metallic terminal points that take up the screws
must be taken into account.
According to DIN 47726, the maximum diameter of a wire with a
nominal cross section of 0.5mm˛ (including insulation) must not
exceed 2.6mm. For a centerline size of 2.5mm, it is therefore
not possible to have lateral actuating elements or guides at the
height of the wire. In order to include the clamping and
actuating elements that act on the wire, the design instead
makes use of the available depth and height dimensions. This is
the space that offers potential for miniaturization.
How compact
can connection technology become while still remaining usable?
For example, it is no longer possible to actuate existing
spring-cage terminals with a centerline size of 2.5mm using the
fingers alone (Figure 1).
The actuating elements lie so close to each other that a
screwdriver is necessary to effectively actuate the individual
poles. For this reason, many manufacturers include
recommendations in their catalogs on which screwdrivers can be
used to actuate the connectors and PCB terminals.
Suitability for SMT Processes
 In
PCB manufacturing, customers are increasingly interested in
connector components that are compatible with surface-mount
technology (SMT) and can be processed together with the other
surface-mount devices (SMD), such as ICs, resistors, inductors,
and LEDs. In SMT processes, components are automatically fed
along a belt to the pick-and-place machine. Once the components
have been mounted, the PCB module is soldered automatically in
the reflow oven and then inspected. The requirements for the
connector components are based on these work steps.
To ensure that the pick-and-place machine can pick the
components from the belt, the suction surface must be large and
smooth. This is the only means of picking the components from
the belt using a standard vacuum pipette and then placing them
onto the PCB. In the reflow soldering process that follows, the
temporary high-temperature stability of the housing, at
temperatures up to 260°C, is very important. The process
capability of the housing is specified in the standard IPC/JEDEC
J-STD-020D (Figure 2).
As with all
surface-mount components, there are additional requirements for
the solder contact surfaces. Most specifications stipulate a
solder surface coplanarity of 100–200µm. This applies to the
solder surfaces of any anchor metals in use, as well as to the
contact solder pin, since the component is bonded to the printed
circuit board through these surfaces. For the plug connector
systems and PCB terminals discussed here, this connection is
most important because these elements are also subjected to
mechanical loading.
Miniature Plug Connectors of the New Generation
Miniaturization, manufacturability, and usability are currently
the main factors determining the feasibility of plug connectors
and PCB terminals for real-world applications. To keep up with
miniaturization trends, new plug connectors and PCB terminals
must become smaller while also being suitable for use in
automated surface assembly. Therefore, it is worthwhile to weigh
the various requirements against each other with the overarching
goal of pushing component miniaturization forwards.
In developing new miniature plug connectors, Phoenix Contact’s
main goal was to ensure that they require as little PCB space as
possible, while still remaining suitable for SMT.
One recent innovation is the PTSM spring-cage connector. This
connector uses a push-in spiral spring as the clamping element.
This type of contact is extremely compact and allows stripped,
rigid, and flexible cables to be connected quickly. The terminal
actuating elements provide additional potential for
miniaturization. If release buttons are no longer included in
the design, that space becomes available. By eliminating the
release buttons, the components can use a flatter and shorter
design. Instead of an additional release button, a screwdriver
is used as the actuator by inserting it into the actuator slot.
A screwdriver with a blade width of 2.0mm—used commonly in
electronics—is appropriate for this function.
 New
technologies are also available for the second type of miniature
plug connector. PTPM connectors are IDC terminals for flexible
wires. The cutting edges were shortened until only a tip
remained. These edges, also referred to as pierce contacts,
function differently from customary blades. These miniature plug
connectors are actuated by hand without the need for tools.
Hinged guides allow proper positioning of the wire. After
positioning the wires, the user must simply insert them using
thumb pressure, and the piercing element will contact the wire
(Figure 3).
This is a simple and quick means of actuation.
Both of these plug connectors demonstrate that common wire
connector elements can be miniaturized even further. Since these
components are only 5mm in height, users save valuable space.
These space savings allow additional functions to be implemented
for each regained unit of PCB space.
Ease of use is ensured through systematic application of the
design attributes discussed above. Sufficiently large suction
surfaces have been made available, especially for the reflow
process. Furthermore, heat-resistant materials are used for the
new miniature base terminals as well as for the PCB terminals.
This represents an important step toward miniaturization of
PCB-based components. The technical data make it clear that
these products are suitable for real-world applications.
Voltages of up to 150 volts UL and currents of up to 5 amps UL
can be transferred across each pole.
The trend toward ever-smaller electronic components presents
many challenges for manufacturers. However, new miniature PCB
connectors with either spring-cage or IDC technology can improve
wiring speed and take up minimal space, and provide more space
for critical components. When small, quick termination
connectors are used in combination with surface-mount
technology, they offer more design flexibility and reduce the
cost of the entire process.
Lukas Muth, Combicon product marketing, Phoenix Contact GmbH &
Co. KG, Blomberg, Germany, is the global contact for Phoenix
Contact’s PCB miniature connectors. Contact him at
lmuth@phoenixcontact.com.
Andrew Bogaczyk is a product marketing specialist for Phoenix
Contact USA. Contact him at
abogaczyk@phoenixcon.com.
Visit Phoenix Contact online. |
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