Staying Connected - July 2011

External Electronic Assemblies

Often the need arises to add electronic capability to an existing medical device without redesigning the device itself.  In this situation one option is to add the necessary electronic capability and components in an external housing connected by a cable assembly to the original device. This is a common situation where legacy devices need to be made compatible with newer technologies.

There is also an increasing need to capture analog physiological signals(such as an ECG or blood pressure), digitize the information, and transmit the digital signal to a host device via a data cable or even wirelessly.  An external enclosure, housing the necessary electronics is often employed.


Hybrid enclosure – inner clam
shell with overmolded outer surface


Clam Shell enclosure with cables
adapts disposable pressure transducers

Enclosure Options

The three most common methods used at Affinity to enclose electronic assemblies are:

  • Clam shell enclosures
  • Overmolded or encapsulated electronic circuits
  • Hybrid enclosures

The optimum enclosure method is dependent on a number of factors including size, durability, ingress protection requirements, cost, development time and the look and feel of the final assembly.

Clam Shell Enclosures


PCB assembly in lower half
of clam shell enclosure


Finished and sealed clam shell
enclosure in-line with cable



Interior of custom enclosure with
flexible strain relief and PCB standoffs

The most common enclosure is a hard plastic clam shell with upper and lower sections that are secured together once components have been installed.  This enclosure may be a simple box with an attached lid or more sophisticated with interlocking groves and a gasket to achieve a waterproof seal.

While stock clam shell enclosures are available from a variety of sources, they are rarely configured as needed.  Openings for cables or connectors may not be in the right location or in the correct size.  Rarely do stock enclosures have appropriate features in the desired location to mount PCB’s or provide anchor points for cables or wiring.


Ultrasonic welding is commonly used
to seal plastic clam shell enclosures


Custom clam shell enclosures can be designed and manufactured to allow them to be reopened or to be permanently sealed.  Often screws are used to reopen enclosures and an adhesive or ultrasonic welding is used to permanently sealed enclosures. 

If an enclosure is designed to be screwed shut, screw placement can often be hidden by labeling.  When a label is used to cover screws, it can also act as a deterrent to tampering because the label will not remain intact if the screws are removed to open the case.  The most common method to seal plastic clam shell enclosures is by ultrasonic welding.

Overmolded Electronics

Of the three options, overmolding active electronic components presents the greatest challenge for manufacturing.  Molding typically involves injecting hot material at high pressure into a cavity where the electronic assembly is suspended.  Any components that standoff from the surface of a PCB or have a high profile can be moved and damaged by the injected mold material.


Complex PCB before molding

In-line Overmolded PCB
assembly is functional and durable

An additional obstacle to overcome when overmolding electronics is the effect on components due to shrinkage of mold material as it cools.  Experience has taught us that this failure mode must be considered when specifying materials, designing tooling and establishing mold parameters.

Overmolding directly over a PCB typically involves an inner and outer mold.  The inner mold adds mechanical strength and is commonly used to anchor any cables and connectors.  An outer overmold finishes the assembly adding the desired look and feel as well as providing space for branding or labeling.




Overmolded PCB assembly adapts
legacy RS232 device to USB port

Molding directly over electronic components adds additional opportunities for failures due to the temperatures and pressures associated with molding.  Because of this, it is generally advantageous to verify the electronics continue to function properly at various stages of the molding process and to conduct a final functional test prior to shipment.

Even with the manufacturing challenges, encapsulating electronic components by overmolding can produce a part that is small, strong, has an appealing look and feel and offers a high degree of ingress protection.

Hybrid Enclosures

Hybrid enclosures are a combination of hard plastic cases overmolded with a softer material such as Santoprene® thermoplastic elastomer (TPE).  There are several advantages to this type of enclosure including protecting the electronic components from the temperature and pressure of insert molding.  Another advantage of a hybrid enclosure is that the look and feel of an overmolded enclosure can be achieved without the weight of a solid molded assembly.


Clear clam shell case holds and protects
circuitry from final overmolding operation


Finished assembly after overmolding
inner clam shell with softer
thermoplastic material

Summary

Incorporating electronic circuits into external enclosures can offer medical device manufacturers additional alternatives.  The Affinity engineering team has experience designing and manufacturing a wide variety of enclosures and incorporating circuits, connectors and cable assemblies.

For more information on how Affinity can help you with external enclosures, custom cable assemblies or connectors, contact us at customercare2@affinitymedical.com or call us at +1 949-477-9495 or visit us on the web at www.affinitymedical.com.

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Meet Minh G Nguyen – Manufacturing Engineer



Minh Nguyen –
Affinity Manufacturing Engineer

Minh joined Affinity Medical just over two months ago as a Manufacturing Engineer after working for St. Jude Medical for more than three years.  When asked what attracted her to Affinity Minh said, “When I interviewed with Affinity I was attracted to the company because of the friendly, family-oriented environment.  Since I have been here

Minh was born in Vietnam and her family immigrated to the United States when Minh was 16 years old.  She graduated from University of California Irvine with a Bachelor of Science in Biomedical Engineering.  Minh continues her education through UCI extension courses studying Medical Device Development.  Through UCI’s School of Continuing Education, Minh is also taking Business Management courses this summer.


Minh reviewing mold parameters
for validation


Affinity Director of Engineering, Bob Frank, commented about Minh: “Minh is a very bright young lady that is driven to achieve success in all that she does.  Her ambition, combined with her education and work background, helped her “hit the ground running” at Affinity.  She has made an immediate contribution to the company by supporting the manufacturing and quality teams.  Minh has worked side by side with our manufacturing technicians to review processes and identify improvements.  She has supported our quality team by documenting and executing validation protocols for new equipment and processes.”



Minh and Affinity Director
of Engineering Bob Frank

Continuing, Bob commented: “Minh has an excellent background in medical device manufacturing and compliance with the FDA CGMP’s.  We are working with Minh to strengthen her design skills using SolidWorks as well as developing a better understanding of the “insert molding process.  Besides contributing on a professional level, Minh is very well liked by her co-workers.  She has a fun, engaging personality and is a person of strong character.”

When asked what she wanted to accomplish on a longer term basis, Minh said, “I want to support new product development, assist the quality group with qualification and verification of new equipment and processes and improve our manufacturing processes.  I am not experienced in insert molding so I have a lot to learn about that.  But, I appreciate the opportunity to work on the IOQ and PQ for our newest molding machine.”

Minh lives with her parents and younger brother in nearby Westminster.  Outside of work she enjoys badminton, swimming, ping-pong and Wii-sports.  For vacation, she enjoys spending time with her family and visiting relatives.

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Using Copper Alloys to Increase Tensile Strength

Minh Most medical cable assemblies use standard stranded copper as the conductor material.  When the appropriate gauge and stranding of the conductor as well as jacket material, insulation and fillers are specified a cable or lead wire assembly that fully meets ANSI/AAMI EC53 requirements for tensile strength can be produced.  If additional performance is desired or required and the gauge of the wire cannot be increased, the one option is to use a high performance copper alloy for the conductor material.
                        
Bare 28 gauge stranded copper conductor, commonly used in lead wire assemblies, has a tensile strength of about 5.2 pounds.  When a shield and jacket are added to the bare copper conductor and terminated properly, the tensile strength is increased.  Tensile strength at the termination is typically above 12 pounds, well in excess of the ANSI/AAMI EC53 requirement of 7 pounds.


Tensile strength comparison copper vs. copper alloy conductor

In comparison, one of the copper alloy conductors often used to improve performance has a tensile strength of approximately 8.2 pounds, about 60 percent higher than standard copper.  With similar construction of a shield and jacket, tensile strength at the termination is above 18 pounds, a significant improvement that results in a more robust wire assembly.

If you would like more information on the option of using a copper alloy to increase the tensile strength or flex life performance of a cable or lead assembly, contact the Affinity Engineering team at +1 949-477-9495 or via email to CustomerCare2@affinitymedical.com.

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Announcements, Information and Trivia


Bowling Trivia

Ancient Polynesians rolled round stones at objects from a distance of 60 feet (18.2 meters) - the same distance as from foul line to headpin in use today.

Dutch Colonists brought bowling to America in the 17th century.  The game consisted of nine pins set in a triangle. It was regularly played in an area of New York City still known as "Bowling Green"


Bowling is the fifth most popular
participation sport in the U.S.


Connecticut banned "bowling at the game of ninepins" in 1841 because of widespread gambling associated with the game.  It is believed that today's game of tenpins was devised to circumvent laws against the game of ninepins

Bowling is the fifth most popular participation sport in the U.S. with approximately 45 million people enjoying the sport.

Bowling was a religious ceremony in Germany during the 3d and 4th centuries.  Parishioners rolled or threw an object at a pin or kegel to avoid performing an act of penance

 

Affinity Customer Care and Hours of Operation



Candy, Suzann and Cesar – the Affinity Customer
Care team - the Affinity Customer Care Team

At Affinity Medical, we don’t have a customer service department.  In place of customer service, we have Customer Care Coordinators.  While our Customer Care Coordinators perform many of the same functions that customer service representative would, we strive to offer our OEM partners more than that.  The job of our Customer Care Coordinators is to take very good care of our OEM customers.

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

 

Affinity Medical Technologies

3545 Harbor Boulevard, Suite 150
Costa Mesa, CA 92626 USA
Phone: +1 949 477 9495
Fax: +1 949 477 9499

Email: Customercare2@affinitymedical.com
Website: www.affinitymedical.com
Blog: http://blog.affinitymed.com