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Technical white paper

A new technology for high current, low insertion force,

low resistance and long cycle life power connectors

Methode has developed a new class of patented 1 power connector named PowerBud TM 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.
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
humans 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
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By Forrest Sass

surface wear, a leading cause of connector failure. Previous efforts concentrated almost entirely on
developing improved contact surface coatings. 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 two different methods to maintain low contact resistance.

1. Increase the size of the mating contacts, which yields many more microscopic points of contact.
The result is a larger, more costly connector.
2. Increase 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.
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. While less conductive than pure copper, beryllium copper is easily fabricated into a
part that serves both as spring and conductor. This solution is widely used today in low cost

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By Forrest Sass

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
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

Methodes 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.

By Forrest Sass

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
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

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.

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By Forrest Sass

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
Methode acquired Tribotek in 2005 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. 2

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.

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By Forrest Sass

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
















Am ps
Competitor Vdrop (mV)

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Pow erBud Vdrop (mV)

By Forrest Sass

Pow erBud vs. com petition tem p rise, 6.4m m or equivalent pin


Centigrade degrees








Am ps
Competitor temp rise C

Pow erBud temp rise C

PowerBud vs. competition mating / unmating force, 9.1 mm pin




4N (0.9 lb)

4N (0.9 lb)


21N (4.7 lb)

13N (3 lb)

PowerBud vs. competition cycle life

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10,000 cycles


1,000 cycles est

By Forrest Sass

PowerBud versions
The PQ panel connectors feature four PowerBud
contacts in a molded thermal plastic housing designed for
blind-mate 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 the PQ panel connector, both

housing four PowerBud connectors. 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 300A @ 600VAC per contact
with a 30C 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 FusionLugs TM.
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
the heat-sinking capability of the mounting medium.

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By Forrest Sass

The PowerBud is a new class of power connector offering lower volatge drop, 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 tempreture 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

Patent issued August 2009

I removed the following text: Methodes global manufacturing footprint and in-house tool engineering expertise will
allow for PowerBud components to be manufactured on multiple continents. This is a commercial message and doesnt
belong in a white paper; it would be appropriate for a sales brochure or perhaps a combination sales brochure/data sheet

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By Forrest Sass