Staying Connected - June 2010

Retention Force for Non-Locking Medical Connectors

Medical connectors can be divided into two broad groups based on how they are retained by the devices to which they are connected: locking, also referred to as latching and non-locking.  Each offers advantages and disadvantages.  This article addresses some of the issues surrounding non-locking connectors.

Locking vs. Non-Locking

Custom locking connector with
positive latch mechanism

Custom non-locking connector mates
securely providing IP67 rating

Example “MS – mil-spec type
connector commonly used
in early medical devices

Early medical cable assemblies used connectors adopted from industrial and military applications.  These “MS” (mil-spec) metal connectors had knurled threaded couplers.  Once screwed down to the receptacle, this connector would not come loose inadvertently.  While this type of connection met the requirement that the cable not be disconnected unintentionally, they were typically difficult to connect and remove and provided no safety disconnect feature which is often desirable for medical applications.

A more up-to-date example of a locking connector commonly used in medical devices is the “RJ” type plug.  Because of the design and materials typically used, the locking mechanism is easily broken.  Once the locking mechanism breaks, the plug is poorly retained by the receptacle and the cable is generally replaced.

RJ connector – Locking mechanism
can be easily broken requiring
the cable to be replaced

Medical cables, particularly those that connect between a patient and a stationary device, often require a safety mechanism that will allow disconnection without harm to the patient or damage to the device or cable.  The need to ensure a reliable connection to the device; yet allow for safe, inadvertent disconnect is a design requirement the Affinity engineering team has experience implementing.

Non-Locking Connectors

Medical cables require a positive connection between the plug and receptacle.  Any looseness in the connection will usually cause intermittent contact, resulting in unwanted noise or poor signal quality which may make diagnosis or therapy difficult, if not impossible.

How firmly the plug is held by the receptacle is referred to as retention force and is controllable in the design process.  Pin and socket selection, as well as the physical design of the plug and receptacle, allow control over both insertion and retention force.

The interface and friction between
pin and mating sockets typically
play a large role in establishing
mating retention force of a connector

Retention Force

Retention force of a connector pair - plug and receptacle - is nominally made up of the sum of the retention force of each socket and pin as well as any friction between the plug insulator and the receptacle walls.  For connector pairs with few contacts, friction between the insulator and receptacle wall may be the largest factor in determining the total retention force.  For units with a larger number of contacts, little or no friction may be needed between insulator and receptacle wall.

Custom connector with retention force
made up of both pin-to socket friction
and plastic-to-plastic interface

An additional factor to be considered is that in a connector with more than a few contacts, the total retention force is greater than the sum of each pin to socket retention force.  This phenomenon is detailed in a paper by Robert S. Mroczkowski, Sc.D “The Mating Game” in “Connector Specifier” magazine, December, 2001.  Mroczkowski states that “mating force will always be greater than that value (if all contacts mate at the same time) because of tolerance and housing interaction effects.”

Retention Force Specification

At Affinity, one of the specifications we establish with our OEM partners early in the project is the retention force of the plug to receptacle.  The amount of retention force as well the required number of mate and un-mate cycles are factors considered in contact selection.

Once mating and retention forces are established and documented, molds are designed in a “tool safe” manner.  Tooling is specifically designed to produce plastic parts that have retention force below the desired level.  By removing metal from the tool, the connector becomes larger and retention force is increased.  This is done in very small increments which allow retention force to be “dialed in.”  Sharing mold trial parts with our customer’s design team allows insertion and retention force to be evaluated and adjusted before production parts are manufactured.

Connector Retention Force Testing

Once production parts have been manufactured, Affinity will confirm that all specifications, including connector retention force, are met by testing.  Lab testing will include measuring retention force before, during, and after the number of mate and un-mate cycles in the product specification.


The desired mating and retention force of non-locking connectors should be established early in the design process.  The engineering team at Affinity Medical Technologies has the experience and expertise to design a custom medical connector to meet your requirements.  Let us become part of your design team.  Contact Affinity Customer Care at 949-477-9495 or email to

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Meet Heather Hibben – Affinity Medical Quality Engineer

Heather Hibben - Affinity
Medical Quality Engineer

Heather Hibben is one of the newest members of the Affinity team, joining the company in early June as Quality Engineer.  Before joining Affinity, Heather worked six years for a company that specialized in aerospace and military components.  It was there that she found her love of quality and functioned both as the Sr. Quality Engineer and Lean Six Sigma Black Belt.

As Affinity continued to grow, the need for a Quality Engineer became apparent.  Affinity Quality Manager, Cindy Oldynski said “The first time I met Heather, I was impressed with her enthusiasm and professionalism.”

When asked what she likes most about her new job, Heather replied, “I really love quality.  I love the level of detail and digging into issues.  When investigating an issue, the obvious cause is often not the root cause.  I like using my six sigma tools to find the real root cause.”

Heather grew up in Huntington Beach in Southern California.  “I am a beach girl at heart,” said Heather.  “I went to school at Kansas University and besides getting a good education, it made me realize how lucky I was to grow up at the beach.”

When asked what her hobbies were, Heather replied “I love to scuba dive.  I have been diving about six years and am a certified rescue diver.  I also love gardening and planted a huge garden in my back yard.  I’m growing everything including watermelon, bell peppers, corn, tomatoes and artichokes. I also have a dog, three cats and a fish who I just love.”

“I am a huge practical joker,” said Heather.  “I love to laugh and try to find humor in everything I do.  One of the things I like about Affinity is everyone is so friendly.  I interviewed five times for this job, but after the first interview, I knew this is where I wanted to work and did not look anywhere else.”

“Believe it or not, I am a Sci-Fi junkie.  I love aliens, monsters and zombies,” said Heather.  I also like to go to the Renaissance Faire and dress up as a peasant girl.”

“The environment at Affinity is so welcome.  The level of commitment and dedication to quality is so refreshing, it literally knocked my socks off,” commented Heather.  “The production team is awesome.  One hundred percent on-time delivery for May shows the commitment.  I’m really happy to be here.”

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Bonded Wire

Connector end of 5-lead
bonded leadwire set

One of the capabilities of Affinity Medical Technologies is offering medical device manufacturers a variety of choices in leadwires.  One option that many have found convenient and cost effective is bonded leadwires.

Bonded leadwires help eliminate wire tangle that is common when individual leadwires are used on Holter, event, or telemetry monitors.  The longer the length and the greater the number of leads, the greater the opportunity is for leadwires to become tangled.  Tangled leadwires can lead to incomplete monitoring, patient discomfort and frustrated practioners.

Affinity Medical Technologies offers both shielded and unshielded bonded leadwires and in various configurations (two to ten conductors) and in several wire diameters and various wire colors.  Almost any length lead is possible and it is common that the bonded wires typically separate into individual conductors 12 to 15” from the patient end.

Bonded leadwires with wire diameter
of 1mm, 1.5mm, and 2mm

Molded rip stop prevents bonded
leadwires from splitting

The engineering team at Affinity has experience in designing bonded leadwire systems for medical monitoring.  If you would like to see samples of cables incorporating bonded leadwires, contact Affinity Medical Customer Care at 949-477-9495 or email to

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Announcements, Information, and Trivia

Independence Day – July 4th

The American colonies legally separated from
Great Britain on July 2, 1776!

On that day, the Second Continental Congress voted to approve “a resolution of independence” that had been drawn up in June by Richard Lee of Virginia.  The Committee of Five, with Thomas Jefferson as its principal author, prepared the Declaration of Independence, a document explaining the decision to take such action.

Richard H Lee is known for
his famous resolution that led
to the United States declaring
independence – src: Wikipedia

For two days Congress debated and revised the document.  The Declaration of Independence was approved July 4th, 1776.

One of the most enduring myths about Independence Day is that Congress signed the Declaration of Independence on July 4, 1776.  Most delegates actually signed the Declaration on August 2, 1776, a month after Congress voted to approve independence.

Venezuelan Independence Day

Venezuela declared its independence from Spain on July 5th, 1811, 35 years and one day after America declared independence from Great Britain.  The declaration proclaimed a new nation called the American Confederacy of Venezuela.

Venezuela was Spain’s first colony in the Americas to declare independence.

Affinity will be closed Monday, July 5th in honor of Independence Day

Suzann Sitka, Cesar Jara and Candy Golding
- the Affinity Customer Care Team

Affinity Customer Care -
Hours of Operation

Affinity Medical Technologies Customer CCare specialists are available to assist you from 7:00 A.M. until 4:00 P.M., U.S. Pacific Time, except holidays.

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Affinity Medical Technologies

1732 Reynolds Ave
Irvine, CA 92614  USA
Phone: +1 949 477 9495
Fax: +1 949 477 9499