Technical white paper
A new technology for high current, low insertion force,
low resistance and long cycle life power connectors
Abstract
Methode has developed a new class of patented power connector named “PowerBudTM” that
successfully overcomes key limitations of conventional power connectors. The PowerBud technology
lowers both contact resistance and contact normal force without increasing connector volume, a feat
that counters conventional wisdom. The resulting connectors exhibit lower insertion force, lower
temperature rise, lower power loss and higher cycle life than conventional high current connectors.
Introduction
High current (>50A) connector design presents many design challenges. At the top of the list is the
need to minimize contact resistance. Lower resistance has the beneficial effect of lowering I2R power
losses, lowering contact temperature, which in turn leads to higher reliability. The lower temperature
rise also allows the connector pairs to be positioned closer together in a connector housing, minimizing
the connector size.
Minimizing power loss is important because of the growing “green” initiatives intended to reduce
human’s adverse impact on the earth. The energy used which is ultimately burned up as connector heat
is wasted energy.
Low insertion force is also highly important. Insertion force is simply the mechanical force necessary
to mate or unmate the connector. Reducing insertion force has the beneficial effect of reducing contact
PowerBud connector
Released 9/17/09
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Methode Power Solutions Group
1750 Junction Ave., San Jose, CA 95112
www.cablecotech.com
surface wear, a major contributing cause of connector failure. Previous efforts concentrated almost
entirely on developing improved contact surface coatings and materials. Other design efforts modified
the pin shape to minimize the insertion force.
This paper discusses the design tradeoffs and innovative methods to optimize current rating, contact
resistance and insertion force, and how those tradeoffs led to the development of an innovative new
power connector technology.
Conventional connector challenges
Manufacturers finely polish and plate mating contact
surfaces in order to increase contact surface area, leading
to a general misconception that current flows through the
entire mated surface area. However, the actual percentage
of that area which actually makes contact with the mating
connector is very small. Fig. 1 shows that a polished
gold-plated mating surface, viewed on a microscopic
level, consists of peaks and valleys called asperities.
Electrical current is concentrated and passes through the
asperities which are in actual contact.
Figure 1: Surface topography showing
asperities on a polished, gold-plated berylliumcopper contact surface
Manufacturers have adapted to the limited amount of
contact area using different methods to maintain low contact resistance, including
1. Increasing the size of the mating contacts, which yields many more microscopic points of
contact. The result is a larger, more costly connector.
2. Increasing the “normal force” pressing the two mating surfaces together, which slightly
deforms the asperities thereby increasing contact surface area. The result is a connector with
high friction force that is more difficult to mate, or an expensive connector mechanism to
provide the additional force after mating.
3. Using a manufacturing process to reduce the surface asperities
The need to mechanically force the mating surfaces together has led to many design compromises.
Since copper is one of the very best reasonably-priced electrical conductors (excluding gold, silver and
other exotic materials), it would be a good choice for the mating parts of the connector. However,
copper has poor mechanical spring properties. If both mating surfaces were pure copper, the connector
would also require an additional spring to maintain copper-to-copper contact. In the connector world,
that yields an expensive product.
A more practical solution is to choose a material with both spring and conductive qualities such as
beryllium copper or tin copper. While less conductive than pure copper, these copper alloys are easily
fabricated into a part that serves both as spring and conductor. This solution is widely used today in
low cost connectors.
PowerBud connector
Released 9/17/09
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Methode Power Solutions Group
1750 Junction Ave., San Jose, CA 95112
www.cablecotech.com
Microscopic look at plated contacts
The actual points of contact between mated
surfaces can have a relatively high resistance
and therefore a relatively high voltage drop.
Each of these points of contact has a finite
resistance.
One way to minimize the overall contact
resistance is to have many points of contact.
By placing lots of contacts “in parallel”,
junction resistance is reduced.
Figure 2. First Contact x/z cross-sectional view taken
across Au contact interface showing potential values
represented as gray scale and height.
Tribotek technology developed by Massachusetts Institute of Technology researchers
Methode’s original WovenBud was developed by a MIT professor and graduate students investigating
tribology, the science and technology of interacting surfaces in relative motion. It includes the study
and application of the principles of friction, lubrication and wear. The company name Tribotek
originates from the word tribology.
The researchers developed a prototype power
connector with superior qualities compared to
conventional, commercial power connectors.
The Tribotek connector, as it was later called,
had very low contact resistance as well as
very low insertion force, without a
commensurate connector volume increase.
Figure 3: Illustration of Tribotek connector
basic elements showing pure copper wire
wrapped around Kevlar tensioning fiber and
held in contact to a copper mating pin.
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Tribotek connector performance is based on
maximizing the number of discrete points of
contact rather than attempting to increase the
contact surface area or polish the mating
surfaces to a finer degree. Furthermore, the
conductors are pure copper to minimize
resistance. Tribotek fabricated a socket-style
connector by weaving pure copper wire
around a Kevlar non-elastic cord held under
tension to produce a connector with many
points of contact around the circumference of
the mating pin.
Methode Power Solutions Group
1750 Junction Ave., San Jose, CA 95112
www.cablecotech.com
The connector technology handles almost 500A with very low voltage drop and very low insertion
force. Because the fabrication of this connector is labor-intensive, it tends to be used for high value
applications.
Contact Termination Body
Metal spring
Conducting wire
Tensioning Fiber (Kevlar)
Mating pin
Figure 4: Photograph of practical Tribotekstyle connector showing wound copper wire,
Kevlar cord and tensioning spring.
How the WovenBud lowers contact
resistance
A single conductor weave has at least four
points of contact and possibly many more
depending on the number of asperities on
each mating surface. Each electrical path
can be modeled as a resistor in a matrix,
which results in four parallel paths. In
addition, the resistance contributed by the
copper wire itself is 4 times lower than the
more frequently used beryllium copper.
The Kevlar spring need only provide
enough force to assure surface intimacy.
The resulting lower insertion force means
less sliding resistance to mate the contact
and therefore less wear over time.
Figure 5: Equivalent resistance
model of a single weave. Figure
6 (left): equivalent resistance of
multiple weaves
By arranging all individual weaves in a circular assembly results in
massively parallel contact points, significantly lowering overall connector
resistance. Low contact resistance means less heat generated under high
current loads and less power loss.
PowerBud connector
Released 9/17/09
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Methode Power Solutions Group
1750 Junction Ave., San Jose, CA 95112
www.cablecotech.com
This design approach has yielded a new type of
connector with exceptionally low contact
resistance as well as very low insertion force. The
only drawback to this approach is the cost of
assembly, which limits the use of this connector to
high value applications.
Methode develops the PowerBud
technology
Methode acquired Tribotek in 2008 and continued to
develop the Tribotek connector. The result was the
PowerBud, an evolution of the WovenBud
technology. It embodies the same design approach –
massively parallel points of contact – but using a
mechanical design that is adaptable to mass
production. The resulting connector has many of the
same electrical qualities of the WovenBud with a
lower production cost.
Figure 7 (above): PowerBud mechanical
construction showing dual contact points on each
finger. Figure 8 (below)photomicrograph of a
PowerBud connector.
The PowerBud uses two rows of conductors arranged
one over the other. Instead of using pure copper for
contacts, the PowerBud uses a proprietary
performance-engineered copper alloy material that is
substantially better than the more commonly used
beryllium copper alloy. The conductors have a larger
cross-section than those on the WovenBud connector
to minimize resistance.
The high performance copper alloy is easily
fabricated using automated processes. In addition,
each copper alloy beam includes a slight indentation
in the finger tip to create dual contact points, adding
to the massively parallel contact points.
The easily fabricated fingers are primarily responsible
for lowering the cost of the connector compared to
the WovenBud (Tribotek) design with little sacrifice
in performance.
PowerBud connector
Released 9/17/09
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Methode Power Solutions Group
1750 Junction Ave., San Jose, CA 95112
www.cablecotech.com
This figure shows the relationships
between three connectors with respect
to contact resistance and insertion
force. Competitive connectors have a
higher contact resistance and higher
insertion force than either the
PowerBud or WovenBud.
PowerBud performance
Pow erBud vs. com petition voltage drop, 6.4m m or equivalent pin
35.0
30.0
25.0
mV
20.0
15.0
10.0
5.0
0.0
140
160
180
200
220
Am ps
Competitor Vdrop (mV)
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Pow erBud Vdrop (mV)
Methode Power Solutions Group
1750 Junction Ave., San Jose, CA 95112
www.cablecotech.com
240
260
Pow erBud vs. com petition tem p rise, 6.4m m or equivalent pin
45
40
Centigrade degrees
35
30
25
20
15
10
5
0
140
160
180
200
220
240
Am ps
Competitor temp rise ºC
Pow erBud temp rise ºC
PowerBud vs. competition mating / unmating force, 9.1 mm pin
Mate
Unmate
PowerBud
4N (0.9 lb)
4N (0.9 lb)
Competitor
21N (4.7 lb)
13N (3 lb)
PowerBud vs. competition cycle life
PowerBud connector
Released 9/17/09
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PowerBud
10,000 cycles
Competitor
1,000 cycles est
Methode Power Solutions Group
1750 Junction Ave., San Jose, CA 95112
www.cablecotech.com
260
PowerBud versions
The PQ panel connectors feature four PowerBud contacts
in a molded thermal plastic housing designed for blindmate applications. Each connector half floats under
shoulder mounting hardware and self-aligns to the mating
connector half. This connector uses a 9.1mm pin rated at
300A @ 400VAC per contact.
The MQuad is similar to and slightly smaller than the PQ
panel connector. MQuad panel connectors are also
designed for blind-mate applications. Each connector half
floats under shoulder mounting hardware and self-aligns
to the mating connector half. Contact terminations can be
crimp wire, wired lugs or busbar attached. The MQuad is
smaller than the PQ, and uses a 6.4mm pin rated at 100A
@ 600VAC per contact with a 30ºC temperature rise.
The Slim Latch is designed for compact applications in
which connector current must be optimized while limiting
connector volume. The Slim Latch connector includes an
integral locking mechanism, eliminating the need for
additional means to mechanically secure the connector. It
uses a 2.4mm pin designed for 10 AWG wire and is rated
at 50A @ 600VAC per contact.
The embedded PowerBud connectors have knurled
outer side walls allowing direct press-fit insertion into
busbars, printed circuits boards and FusionLugsTM.
Installation or press-in is accomplished using any flat
surface and does not require any special tooling. The
current rating is dependent on the physical size of the pin
and the heat-sinking capability of the mounting medium.
PowerBud connector
Released 9/17/09
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Methode Power Solutions Group
1750 Junction Ave., San Jose, CA 95112
www.cablecotech.com
Conclusion
The PowerBud is a new class of power connector offering lower voltage drop resulting in lower
temperature rise and lower insertion force than competitive connectors and much less than
conventional connectors. The unique mechanical construction evolved from the Tribotek connector, a
pioneer design which delivers a quantum improvement in power connector performance.
PowerBud allows more current to pass through a connector that occupies a small volume, potentially
reducing package footprint. The lower voltage drop can eliminate the need for a local voltage regulator
module. The lower temperature rise reduces system thermal load.
The PowerBud is suitable for systems that require connectors capable of handling hundreds of amps of
current. It is particularly suitable for systems that require the connector to be mated and unmated
frequently.
PowerBud connector
Released 9/17/09
Page 9 of 9
Methode Power Solutions Group
1750 Junction Ave., San Jose, CA 95112
www.cablecotech.com