Staying Connected - January 2013

Encapsulating Electronics within Medical Cables

As medical devices become more sophisticated, requirements for medical cables and interconnect systems are becoming more complex.  This often leads to the requirement that electronics to be incorporated into a connector or cable system.  A cable assembly in which active electronics have been incorporated is often referred to as a “smart cable.”

If the need arises to add electronic circuitry to a medical device without redesigning the device itself, one option is to add the necessary electronics in an external housing connected by a cable assembly. This is a common situation where legacy devices need to be made compatible with newer technologies.

Cooperation between device manufacturers has increased the need for dissimilar medical devices to be interconnected.  One way to facilitate communication between different devices is to use an external cable assembly with imbedded electronics to manage inter-device communication.

Common Methods to Encapsulate

Common methods used to encapsulate electronic circuits are:

  • Conformal coating and potting
  • Direct overmolding
  • Clamshell housings
  • Hybrid enclosures

Examples of direct overmolding, a clamshell enclosure
and a hybrid overmolded enclosure

The optimum 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.



Protective conformal coating applied
over a portion of PCB assembly

Conformal Coating and Potting

Traditional methods to protect electronic circuits include conformal coating and potting.  Conformal coatings are typically higher viscosity liquids that are applied directly to circuits.  The material flows around and often penetrates small spaces, conforming to the geometry of the components.

In potting, a compound is applied over a circuit until it covers some or all of the components. Once the potting compound cures and solidifies it effectively renders the components into a solid mass, offering protection against moisture, dust and vibration.  Potting is also used to enhance electrical isolation of components and contacts.

Neither conformal coating nor potting provides a surface suitable for user contact.  Both methods are typically used where the circuit will be encapsulated or contained within an enclosure.

Low Pressure Molding


Low pressure molding press facilitates
encapsulation of components


Low pressure molding is an alternative to traditional potting and offers a more complete encapsulation.  In low pressure molding the parts to be molded are held in a tool while a hot melt adhesive is injected at low pressure and relatively low temperature.  The liquid material flows well, surrounding even small components.  Cooling, the material solidifies, and provides additional mechanical strength and moisture protection as compared to traditional potting.

Similar to potting, low pressure molding is generally not considered suitable for direct user handling.  The material as most commonly used is dark amber and somewhat translucent.  Because adding a pigment changes the properties of the material it is not commonly colored.

Low pressure molding has found use as a replacement for the inner shot in two-stage overmolding.

Direct Overmolding

Of the three options, direct overmolding active electronic components presents the



Example of direct overmolding
of active components to produce
a rugged cable assembly

greatest challenge for manufacturing.  Overmolding typically involves injecting hot thermoplastic material at high pressure into a cavity where the electronic assembly is suspended.  While the temperature of the injected material does not typically cause solder to reflow, the mechanical forces present in the injection process can damage the components and affect the electrical integrity of the assembly.

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

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

Direct overmolding of electronic components adds additional opportunities for failures due to the nature of the molding process.  Because of this, it is generally advantageous to confirm that the electronics are functioning properly at various stages of the molding process and to conduct a final functional test.

Even considering the manufacturing challenges, encapsulating electronic components by overmolding offers a number of advantages:

  • Is durable and improves resistance to vibration and shock
  • Has an appealing look and tactile feel
  • Offers a high degree of ingress protection
  • Is more difficult to reverse engineer, adding a level of security         

Clamshell Enclosures

One common alternative to directly overmolding electronic circuit boards is using two injection-molded clamshell pieces that fit together, holding the electronics package.  This enclosure may be a simple box with a top, or a more sophisticated enclosure with interlocking groves and a gasket to achieve a waterproof seal.


A custom clamshell enclosure, before
the top is ultrasonically welded in place,
protects PCB with active components


Stock clamshell enclosures are available from a variety of sources, but they are rarely found in the exact configuration needed.  Openings for cables or connectors may not be present, may not be in the right location or of the right size.  Rarely do stock enclosures have appropriate features to mount PCB’s or provide anchor points for cables or wiring.

An alternative is to design a custom clamshell enclosure.  A custom clamshell enclosure can be designed to precisely match the size of the electronics package and can also be contoured to look like it is part of the cable assembly.

A custom clamshell can be designed to be permanently sealed or reopened, depending upon the application.  Ultrasonic welding or adhesive is commonly used when the enclosure is permanently sealed and screws are often used when the enclosure is designed to be reopened.  If an enclosure is designed to be screwed shut, screw placement can be hidden by placing a label with branding or instructions over the area where screws are located.  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.

Hybrid Enclosures

Hybrid enclosures are a combination of hard plastic cases overmolded with a softer thermoplastic material.  Typically for this type of construction, the clamshell case is filled with a light weight potting material before being overmolded.  If this is not done, mold pressures could collapse the case.


Hard plastic case holds and protects
electronics during overmolding of this
hybrid enclosure


Finished assembly has soft tactile
feel after overmolding with
Santoprene® TPR material

There are several advantages to this type of enclosure including:

  • Protecting the electronic components from the temperature and pressure of direct overmolding
  • Achieving a lighter weight assembly by using a fill material that is lighter in weight than mold material
  • Producing larger overmolded electronic packages than could be achieved by direct overmolding.

With a hybrid design, the outer mold can be designed to follow the contours of the inner case allowing a uniform wall thickness.  A uniform wall thickness will typically produce a more consistent outer surface even when large assemblies are encapsulated by overmolding.



Custom overmolded hybrid
enclosure housing sophisticated
active electronic circuitry

Summary

Encapsulating electronic assemblies 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 David Moreno – Affinity Engineering Assistant



David Moreno,
Affinity Engineering Assistant

David joined Affinity in January 2010, working as a production team member.  Shortly thereafter, he moved into maintenance where he learned to set-up different machines and equipment and maintained mold tooling.  

He was promoted to Engineering Assistant and lab technician in October 2011 and spent about a month working with Bob Evans before he retired.  As Lab Technician, David executes test protocols which confirm the performance of connectors and cable assemblies that Affinity has designed and manufactured.  Occasionally, he will test cable assemblies manufactured by others to “base line” their performance.

David reports to Affinity Engineering Manager, Matt Pathmajeyan, who commented, “When Bob Evans announced his retirement from Affinity, we knew that his shoes would be quite difficult to fill.  But, David jumped right in by learning the appropriate standards and test methods relevant to the types of cables Affinity Medical produces.  David understands how cables are built and routinely assists in determining root causes and potential issues with cable designs.  He always willing to help and is a valued member of our engineering team.”


David pre-conditioning cables
by wiping with cleaning agents
prior to verification testing


In any given month, the Affinity lab executes about six test protocols some which involve testing more than 100 cable assemblies.  Testing includes flex testing, tensile strength, hi-pot, defibrillation withstand, triboelectric noise and torque testing.  In addition to testing, David will pre-condition cable assemblies to simulate how cables are likely to be cleaned and disinfected in a clinical setting prior to doing the actual performance testing.

When asked what he likes about working at Affinity, David responded, “I like the family atmosphere Affinity has.  People that work at Affinity are friendly and nice.  I am very impressed with Affinity and how much it has accomplished.  I have seen the company grow so much since I started working here and I am confident it will continue growing.”

Asked what his short-term goals are, David replied, “My short term goals are to graduate and earn my BA from Cal State Fullerton.  Longer-term, I would like to move up to a management position where I can use the skills and knowledge I have acquired from people and my schooling.  Owning a restaurant is another one of my goals!”

Discussing the skills he brings to his job, David said, “I am a hard worker and a quick learner.  I think that I am good with time management and also good at analyzing and solving problems.”



David performing tensile strength
testing on cable assembly

David has an Associate degree in Business Administration and Liberal Arts degree from Santa Ana College.  He is currently attending California State University Fullerton working on a Bachelor of Arts degree in Business Administration with a concentration in Operational Management.  “Working full time, my biggest challenge is finding time to study,” said David.

David grew up in nearby Santa Ana and Orange and continues to live in the City of Orange.  He has an older brother who he enjoys “hanging out with” and trying new restaurants and different ethnic foods.  ” I like to eat Italian, Greek, Asian, and Indian food. I enjoy cooking spaghetti, pork shoulder with adobo (a red sauce used to marinate meat), and grilling during the summer, “said David.
David also enjoys outdoor activities like biking and jogging and also enjoys cooking for family and friends.  For vacations, David says he likes going to Las Vegas.  “I like going to the different casinos, shows, clubs and buffets.”

Affinity General Manager Bob Frank commented, “David is an articulate, hard working person with a strong desire to learn new skills.  He is also a very strong team player, willing to assist manufacturing, quality or engineering with whatever task that requires lab input.  We’re glad to have him on the Affinity team.”

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Medical Device Excise Tax


The Medical Device Excise Tax is specified by Section 4191 of the Internal Revenue Code.  It imposes a 2.3% excise tax on the sale of certain medical devices by the manufacturer or importer of the device. The tax became effective January 1, 2013

“Affinity cannot make a determination as to whether or not a device that we manufacture for one of our OEM partners is subject to the tax or not,” commented Affinity Business Development Manager, Hank Mancini.  “We have asked each of our OEM partners to make that determination and let us know whether or not we should be charging the tax on the products we manufacture for them.  For customers that have not responded, we began charging the excise tax as a separate line item on customer invoices on January 2nd.”

“Many of the products manufactured by Affinity are clearly not finished medical devices,” said Hank.  “It is imperative that our OEM partners use their knowledge of how the products we manufacture for them are used or sold to determine whether or not the product is considered taxable.  Affinity considers the medical device excise tax as just that, a tax.  Being a tax, it is not part of the cost or price of the product.  It will be invoiced, collected and remitted where appropriate.”

Since the implementation of the Medical Device Excise Tax, Affinity is clearly stating in quotations that any tax due under the statute is the responsibility of its OEM customers.  Without other instructions, Affinity will invoice the tax as a separate item and remit the tax as required by the statute.

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Announcements, Information and Trivia



Lowest temperature
recorded was in Antarctica


Fastest
temperature drop


Snow on Hawaii’s
Mauna Kea

Chilling Facts

The coldest temperature ever recorded on earth is −89.2 °C (−128.6 °F) at Vostok Station in Antarctica on July 21, 1983.  Vostok is located 3,500 meters (11,482 feet) above sea level.

Fastest temperature drop ever recorded was 27.2 °C (49 °F) in 15 minutes in Rapid City, South Dakota, U.S.A. on January 10, 1911.

The coldest inhabited place on earth is Oymyakon, a village in Oymyakonsky Ulus of the Sakha Republic in Russia.  It has the coldest monthly mean temperature: −46 °C (−51 °F), for the month of January.

The lowest temperature ever recorded in Hawaii was -11.1 °C (12 °F) at the Mauna Kea Observatory located at 4,198 meters (13,773 feet) on May 17, 1979.

The snowiest place in the United States is Valdez, Alaska, which receives an average of 8.3 meters (326 inches) of snow every year.