Staying Connected - July 2012

Copper Conductors Use in Medical Cables



Nearly half of all copper mined
is used to manufacture electrical wire

Copper wire is by far the most common electrical conductor used in the manufacture of medical cables.  Today, nearly half of all copper that is mined is used to manufacture copper wire.  Copper is one of the few metals that is more widely used in its pure form rather than as an alloy.

Copper wire has a number of beneficial properties when used as a conductor for medical cables including:

  • Excellent electrical conductivity
  • High tensile strength
  • Good ductility
  • High fatigue resistance
  • Excellent corrosion resistance
  • Low coefficient of thermal expansion
  • Excellent solderability

Electrical conductivity


Copper is the most common
conductor used for electrical wire

All medical cables transport an electrical signal.  Electrical conductivity is a measure of how well a material transports an electric signal or charge.  Copper has the highest electrical conductivity of all non-precious metals.   Because copper has excellent conductivity, the conductivity of other materials is stated as a percentage of the conductivity of copper.

The International Annealed Copper Standard (IACS) was established in 1913 by the International Electrotechnical Commission (IEC).  The commission established the standard for the conductivity of annealed copper which is still used today.

Electrolytic Tough Pitch Copper

The standard grade of copper used in electrical wire is 99.95% Copper (Cu), 0.02 to 0.05 % oxygen, and less than 50 parts per million other metals. It has very high electrical conductivity, in excess of 100% of the IACS.  In the cast form it is called Electrolytic Tough Pitch (ETP) copper.  This grade of copper is often referred to as CA-110 and meets ASTM B152 specifications.  While CA-110 is one of the purest forms of copper it is also referred to as “110 Alloy.”  The conductors of most medical cables are CA-110 copper.

Silver is the only metal with a higher electrical conductivity than copper. The electrical conductivity of silver is 106% of that of annealed copper on the IACS scale.  But, because of the high cost of silver and its low tensile strength its use is limited to special applications.

Annealed copper

Annealing is the process of heating a metal to make it softer and therefore more flexible.  Annealing is particularly effective for copper and annealed copper is much softer than un-annealed copper.  All copper used for electrical conductors, and therefore in medical cables, is annealed copper.

Tensile strength

Tensile strength is a measure of the maximum stress a material will sustain with uniform elongation.  Annealed copper’s tensile strength is 200-250 N/mm2.  For copper wire, tensile strength is generally considered the amount of axial force required to pull wire until breaks.

For wire used in medical cables, tensile strength is often referred to as nominal break strength and is given in pounds or killograms.  As an example, 28 gauge annealed copper wire made up of 19 strands of 40 gauge wire has nominal break strength of 5 pounds or 2.3 kilograms.  If a higher tensile strength conductor is required, the options are to use a larger diameter wire or use a higher strength copper alloy.

Ductility

Ductility is a material's ability to deform under tensile stress.  Copper has a higher ductility than other metals used as conductors with the exception of gold and silver.  Because of copper’s high ductility, it is easy to draw down copper to the small diameters needed for the manufacture electrical wire.

Normally, the stronger a metal is, the less pliable it is.  However, this is not the case with copper.  Copper’s combination of high strength and high ductility make it an excellent material for electrical wire.


The Statue of Liberty is
cloaked in copper to reduce
damage from corrosion

Corrosion resistance

Copper naturally resists corrosion from moisture, humidity, and other atmospheric influences.  Electrolytic tough pitch (ETP) copper is not subject to galvanic corrosion when connected to other, metals and alloys.  This characteristic allows copper to function well as an electrical conductor over a long period of time.

Materials that corrode typically loose flexibility.  Because copper is corrosion resistant, the flexibility of cables and wire used in medical applications is not reduced due to corrosion.

A good example of copper’s corrosion resistance is the Statue of Liberty.  The statue is cloaked in copper and stood exposed to the elements for 100 years before being refurbished.  When it was refurbished, oxidation on the copper skin was measured at less than .005” (.127mm).

Coefficient of thermal expansion



Copper’s low coefficient of thermal
expansion makes reliable and long
lasting wire terminations possible

Most materials expand upon heating and contract upon cooling.  This is an undesirable characteristic in electrical or electronic assemblies.  Copper has a low coefficient of thermal expansion when compared to other electrical conductors.

The low coefficient of thermal expansion of copper is beneficial because electrical terminations, such as solder joints, could easily be compromised by cycles of expansion and contraction.

Solderability


Copper conductors are readily soldered
using either leaded or lead-free solder

Soldering is the process of joining two metals by the use of a material that has a lower melt point than the material being joined.  Because of the high melting point of copper, 1,083˚ C, copper can be soldered with a wide variety of solder alloys.

A characteristic of copper is that it easily “wets out.”  This allows solder to flow and form a smooth, uniform and unbroken coating on copper wire or traces.  Because surface oxidation of copper is minimal, common varieties of flux are sufficient to remove that oxidation which, in turn, allows the surface to wet-out and facilitates soldering.

Stranding copper conductors for increased flexibility

While annealed copper is ductile and is easily flexed, flexibility may be increased by combining a number of smaller conductors into stranded wire.  Stranded copper wire is a group of smaller copper wires that are braided or twisted together.  Stranded copper wire is more flexible than a single-strand of copper wire of the same diameter.


Two versions of 28 gauge conductors
– one with 7 strands and one with 19


The smaller the diameter of the individual strand, the smaller the bend radius

Stranding improves the flex life of copper conductors because the bend radius of each of the smaller conductors is less than that of a single larger conductor.  As copper is repeatedly bent, it undergoes stress which makes it less flexible due to a characteristic called “work hardening.”  For flexible conductors this is an undesirable trait and can lead to conductors breaking under the stress of repeated flexing.

This potential mode of failure can be reduced by using strands of copper with a smaller diameter.  The smaller the diameter, the smaller the bend radius and the smaller the bend radius, the less stress individual conductors are subject to.  The less stress the material absorbs, the longer it will last.

Coating copper conductors

While copper resists corrosion, the surface of bare copper slowly combines with oxygen to form a thin layer of copper oxide.  At higher temperatures, such as required for soldering, this reaction is accelerated.  The oxide that forms on the surface of copper is a poor conductor and is best prevented from forming.

One way to prevent surface oxidation of copper conductors is to coat the copper with another metal which oxidizes more slowly than copper.  The two most common coatings are tin and silver.

Tin oxidizes much more slowly than copper, is readily available and is a relatively inexpensive material.  It is commonly used as a protective coating for copper conductors.  And, because most solder is tin based, achieving a high quality soldered termination is easier using tinned copper as compared to bare copper.

Because silver has a much higher melting point than tin, it is used as a coating where wire terminations will be subjected to higher temperatures. Tin-coated annealed copper wire is normally manufactured to conform to ASTM B965 and silver coated annealed copper wire to ASTM B298-07.

Copper alloys

Where the desired flex life cannot be achieved by using smaller individual conductors, or where a higher tensile strength is required, conductors made of copper alloys can be specified.  Before RoHS and REACH requirements were nearly universal, the most common materials to alloy with copper to improve tensile strength and flex life were cadmium and chromium.  Cadmium/chromium/copper alloys typically offered over 25 times the flex life of pure copper with only about a 10% increase in resistance.

Cadmium-free copper alloys are becoming more commonly available and offer flex life and tensile performance near that of copper alloys that contain cadmium.



Copper wire is at the heart of all
medical cable assemblies

Summary

While the Affinity engineering team has a great deal of experience designing medical cable assemblies we do not do this independently.  The most appropriate raw cable designs typically come from collaboration between our cable extrusion partners, Affinity and our OEM customer.

If you would like to take advantage of Affinity’s experience and expertise in providing robust, long lasting cable assemblies, we welcome you to contact us at +1 949-477-9495 or via email to CustomerCare2@Affinitymedical.com.

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Meet Hank Mancini – Affinity Business Development Manager


Hank Mancini

“I have the best job in the world,” said Hank Mancini.  “I love the company that I work for, love the people that I work with and love our OEM customers.”

Hank joined Affinity in January 2007, bringing with him more than 30 years experience in the medical industry.   As Business Development Manager, he is responsible for all sales and marketing activities for Affinity and reports to company president and CEO Mary Phillipp.

Although Hank’s title is Business Development Manager, he enjoys being involved in all aspects of the company.  In addition to selling, Hank manages the Sales Group and Customer Care team.  He also oversees marketing – including the company’s web site, “Staying Connected,” this electronic newsletter, trade shows and monthly card mailings.  “I like to keep busy and one way to do that is to always be working on several projects.  If there is any down time for one project, I always have something productive that I can be doing on another project,” said Hank.

When asked what he likes most about Affinity, Hank replied, “I really appreciate the customer focus that Mary insists on.  Mary understands that without our customers there is no need for Affinity.  She wants our customers to love us and that is a perfect fit for me.  Mary has assembled a wonderful and talented team and that makes Affinity a great place to work.”

Much of Hank’s time is spent traveling to visit medical device customers and prospective customers across the country.   “Travel is expensive in terms of both time and money, but there’s no substitute for face to face personal contact,” said Hank.  “Most of our customers know us as people, not just the company we work for.”



Hank and Teresa on the floor
at Staples Center

When asked to tell something interesting or unusual about himself, Hank said, “In 1983 I stayed at the Maui Marriott, the chain’s 100th hotel.  I enjoyed it so much that I set the silly goal of staying at all 100 Marriott hotels.  In 2001, I reached my goal; having stayed at 100 different full-service Marriott hotels (they now have thousands!).  One of my proud possessions is a personal letter from Bill Marriott recognizing the attainment of my goal.  It hangs on my office wall.  Since then I have stayed at another 49 full service Marriott hotels so sometime this year I hope to hit 150.”

“I had never attended, or even watched an NBA game on television until 2000.  I asked my wife what she wanted for Mother’s day and she said she wanted to go to a Lakers game.  Well, Mother’s Day is during the playoffs so I had to buy tickets on eBay.  We went to a game and we were both hooked!   We spent our vacation money buying tickets to the rest of the playoff games and saw the Lakers win the first of three consecutive championships.  We have been season ticket holders since then and both of us are pretty passionate about the Lakers.”

Hank and his wife Teresa live in Huntington Beach, California.  They share six grown children and have four grandchildren.   Besides being a Lakers fan, Hank enjoys digital photography, reading, red wine, dark chocolate and everything Marriott.  Hank is a big fan of the TV reality shows The Amazing Race and Survivor.  “If I could ever justify taking six to eight weeks off, I would try to get on The Amazing Race with one of my kids.  The million dollar prize would be secondary to winning the race!”

Hank and Teresa share their home with Kobe, a 9-year old pug, Magic their cat, and Gumby an Eclectus parrot.

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Field Termination Kit

Occasionally, it may be desirable or even necessary to update cables in the field with a new connector.  This can happen when a manufacturer introduces a new device yet has a large installed base of cables with an incompatible connector.  One option is to replace all of the cables in the field with a new cable assembly.

Another option is to modify cables in the field by adding a new connector.  For this to be a viable option, changing the connector needs to be easily accomplished and the modified cable needs to meet all performance, safety and regulatory requirements.


Components of Affinity designed
Field Termination Kit


Field assembled connector has the
look and feel of a molded connector

Affinity has designed and manufactured Field Termination Kits.  Each is designed to be installed by either the manufacturer’s service team or a biomedical engineer.  The field installed connector is designed so that once terminated to the cable and assembled, it is difficult to remove or disassemble.  The finished assembly has the look, feel and performance of an overmolded connector.

If you would like more information or a sample of a Field Termination Kit, contact the Affinity Customer Care team at 1+ 949-477-9495 or email at Customercare2@affinitymed.com.

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Announcements, Information and Trivia



Gold, Silver and Bronze
medals – a symbol of
Olympic achievement

Olympic Trivia

The Third Time’s the Charm - London will be the only city to have hosted the Olympic Games three times: 1908, 1948 and now 2012!

Bye Bye Birdie - Pigeon shooting was one of the events in the 1900 Olympics held in Paris France!  It was the only time that animals were killed as part of an Olympic event.

Don’t Pull My Leg – It may seem strange to some today, but Tug-of-War was an Olympic event from 1900 to 1920.  In modern Olympics, Tug-of-War was between two eight-person teams. The winning team was the one that could pull the other team six feet.  If no team had won after five minutes, the team which had pulled the greatest distance was declared the winner.  In 1904, teams from the United States placed first, second, third and fourth!



Tug-of-War was an
Olympic event from
1900 to 1920


Christa Luding-
Rothenburger in 1988
– image courtesy of
German Federal Archive
via Wikimedia Commons

Juggling Priorities - Club Swinging has appeared twice in the Olympics, in 1904 and 1932.  In the event, the competitor stood erect with a club in each hand.  The clubs were similar to bowling pins, and were whirled or swung very quickly around the head and body in a variety of patterns.  Points were awarded by the judges based on the complexity and technique. Unlike juggling, the clubs did not leave the hands.

Hot and Cold Winner - East German Christa Luding-Rothenburger is the only person to win medals at the Winter and Summer Games in the same year.  In 1988 she won the gold medal in Speed Skating in Calgary and a silver medal in Track Cycling in Seoul.  Because the summer and winter games are now held two years apart, Christa’s record will not be broken!