Overmolded Cable Assemblies Guide: Expert Techniques

This is a comprehensive look at the versatility of overmolded cable assemblies and other encapsulating techniques.

Types of overmolded cable assemblies

This is a comprehensive look at the versatility of overmolded cable assemblies and other encapsulating techniques. There is a growing need for connecting individual pieces of equipment, electronic assemblies, and even multi-point cable connectivity for complex equipment. This deep dive into the broadening scope of overmolded cable assemblies is meant to stimulate the imagination by showcasing the versatility of overmold and other encapsulation techniques.

Connector Overmolds

The simplest assembly that may require an overmold is a connector, usually with a cable attached – typical of a connection from a laptop computer to a peripheral. In this case the primary purpose of the overmold is to protect the potentially fragile transition from a cable to the connector plug.

In addition, it ensures the preservation or improvement of the environmental protection rating, especially should there be any potential dust or moisture exposure.

Lastly, there is usually, though not always, some flexibility designed into the overmold portion of the assembly where it attaches to the cable. In this case, it acts as a strain relief and potentially to allow for better cable routing away from any obstacles when installed.

There are a couple of things worth noting in the examples shown above: In the first example, the secure locking feature often found in these types of connectors is easily accommodated in the final design; and in the third example several connector types are built in to the body of the overmolded section. This latter example saves space and illustrates how this design technique expands the capabilities to a multi-connector capability.

All three examples also have a strain relief built in at the cable exit. In the case of circular connectors, it is not always easy to find the correct orientation. A simple solution is to mold in a feature that aligns with the mating part. These are the sort of small details that you can get with a custom design that ultimately make the connection schemes work that much better. Other enhancements can include thumbpads, logos and part numbers, to name a few.

Connector + Electronics: Encapsulation

encapsulated usb illustration

One design capability that not everyone is aware of is the possibility to use the overmolded structure as a convenient location to embed some electronics. Given the improvements in capability and reduction in size of electronics it makes sense to add functionality directly into the overmolded section for a connectivity solution with little to no penalty in real estate.

With the popularity of USB drives, there is the potential for a lot of features to be added in these seemingly simple devices. They already have power which comes from the USB port. If you had x-ray vision you would also see the variety of options for this physical format including solid-state memory, an oscillator (for timing), wireless communication, room for memory expansion, LED lights and so on.

In fact the USB port has been such a popular platform that there are designs that act as drivers for mice, keyboards, external hard drives, webcams, digital cameras, game controllers, mobile devices, and numerous other peripheral devices and accessories.

In this first illustration, the overmolded rendering has a sight transparency to reveal the electronics encapsulated in the USB drive. Note that this version contains a small blue LED overmolded with a translucent material to indicate at-a-glance that the device has power.

complex adapter that combines electronics with three connectors

Of course, the concept of embedding computing power into the connector/cable assembly is not limited to USB ports. Above is a fairly complex adapter that combines electronics with three connectors. In fact, materials selection and designs can be built to withstand saltwater, acids, fuels, hydraulic fluids, and other harsh environments. With the use of high-performance materials, we provide molded PCB and encapsulated PCB designs for assemblies that help protect the circuits and components from the outside world.

These techniques are also capable of very compact and complex structures for multi-point connections.

compact and complex multi-point assembly

Connector/cable end-to-end and multipoint solutions

A logical extension for an overmolded cable assembly is to build complete connector/cable end-to-end solutions. These types of overmolded solutions are common in medical equipment and Military/Defense applications where the connection scheme needs to be foolproof. Wherever you have an overmolded cable assembly, custom cable overmolds can be created with ISC’s in-house tooling.

Often times an existing or standard overmold is available to fit most connectors. Above, you can see a selection of complex designs, often with demanding environmental protection needs. This selection of connector/cable assemblies also showcases the variety of connector types for which overmolds have already been developed. The in-house design library of connector-to-cable overmolds numbers over 1000, meaning that there is a good chance we would already have the overmold tooling (or something similar) that would solve your particular issues.

Tooling overmolded cable assemblies

overmold tooling

Starting with the connectivity question, customers work closely with the ISC design team to define what functionality they are hoping to achieve. This defines the connectors, cable size, material, and grounding/shielding requirements. Most often, the major piece of tooling is for the mold itself to capture the connector plus the attached cable assembly. Depending on the requirements there may be some additional fixturing needed to ensure that the connector and the cable bundle are in the correct orientation to minimize any excess stress in the finished assembly.

An example of mold tooling for a specialized connector assembly is shown here. In this example, it can be seen that the mold can produce two overmolded cable assemblies at a time. This doubles the production rate at a minimal added cost. You can also see that there is a cable capture feature built-in at the cable exit of the mold to help with proper alignment of the cable during the molding process.

Mold tooling needs to be durable in order to maintain its dimensions within tolerance for the intended product process. For a robust process, on long production runs, manufacturing products in the range of 100’s of thousands of units, then steel is generally preferred. However, for shorter runs, prototypes, low-pressure molds, or materials without any potential abrasive additives (i.e. glass beads) aluminum is a perfectly fine alternative. The choice depends on the circumstances. Both materials have their use cases.

Single and Multi-Cavity Molds

It’s worth highlighting the difference between single and multi-cavity molds. The image accompanying the previous paragraph shows a multi-cavity mold. It is easy to see that this mold will create two overmolded connector/cable assemblies as one cavity is identical to the other, however, it has been rotated 180 degrees around the X-axis to keep the mold compact and maintain symmetry. Symmetric molds generally will fill and cool more uniformly.

This mold could be expanded further by rotating the whole mold 180 degrees around the Y-axis to create four cavities. In fact, it is very common in larger multi-cavity molds for them to be designed in this way. Subsequent rotations tend to build up these types of molds from two cavities to four, then 8, 16 and so on. These techniques allow the manufacturer to produce multiple identical parts, thereby improving the production rate for these parts. A higher production rate is usually the reason for choosing a multi-cavity mold in the first place.

There is a special case of a multi-cavity mold called a family mold. It uses the same sort of principles as a multi-cavity mold; however, it is not intended to produce identical parts. The purpose instead, is usually to create similar parts.

One example might be for two different cable assemblies using the same cable but two slightly different-sized circular connectors.

Another example might be when making two parts that need to mate together precisely. In that case, any variations in temperature that might lead to variation in the parts would affect both parts in the same way. This ensures that they will still mate together properly even with some slight part-to-part variation.

Another advantage of a family mold is that since the parts will be used together they will have identical color-matching for a clean professional look.

Encapsulation of electronics

Encapsulated PCBA assembly

As we have seen earlier, it is possible to incorporate electronic assemblies directly into cable assemblies for certain applications. This is accomplished by a process called encapsulation. Encapsulation can be done either by dipping the printed circuit board assembly (PCBA) into a viscous liquid, often a type of epoxy, or by potting. In the case of potting the PCBA is enclosed in a mold and the potting compound is injected or poured into the mold and then cured by heating it for a period of time at a specific temperature.

Encapsulated PCBA electronic

However the electronic encapsulation is done, it usually serves to meet as many as three objectives.

The first objective would be the overall protection of the electronics from the environment, especially moisture, dust, or chemical exposure that could lead to premature failure of the electronics.

A second objective is to physically stabilize the components on the PCBA against shock and vibration. This can be especially critical if a cable ground is incorporated into the design. Failed ground connections are notoriously hard to track down. It’s a best practice to avoid the failure in the first place.

And a third objective would be the protection of the intellectual property that is contained in the chips themselves and/or any programming contained in memory. For this last purpose, it is common to use an opaque, black potting compound. This would prevent someone from visually gaining any information without likely destroying the PCBA itself.

When a Premold is needed

overmolded cable assembly

One step that can be incorporated, when appropriate is the use of a pre-mold. This is a shaped part that can serve a variety of purposes. It does provide some added structural integrity to the finished part and fully encapsulates the critical terminations providing some strain relief to the assembly. It also helps to maintain the contour in the transition from the connector to the cable. To some degree, it can also be part of the flow regime when the final overmolded material is injected – providing a smooth and aesthetic finish on the final part.

Advantages of vertical integration

Imagine you are a designer working on a complex piece of electronic equipment. You have found an error in the first round prototype: an interference on a mating part that you did not anticipate. You need a quick-turnaround modification on the part. Your supplier uses an outside contractor to re-machine the mold for the part which will add two weeks to the project.

That situation is precisely why ISC has arranged their shop so that time-critical steps can be performed in-house with existing equipment. They have vertically integrated the manufacturing and assembly processes, soldering, mechanical assembly, mold design, injection molding, and electrical testing. They carry a whole host of competency certifications from a wide range of international agencies including ITAR, NASA, IPC workmanship standards, ISO 9001, and QPL/QML as well as environmental regulatory agency standards like RoHS and REACH.

Overmolded cable assemblies: fit and finish

This is not really a technical engineering term, but it is a term that speaks of the overall quality of a completed assembly. It refers to the physical attributes that you would expect to see and feel in a well-made product.

Is the product smooth and uniform where it needs to be?

Are there smooth transitions from one section to the next?

Does it fit well in the hand (assuming it is meant for use by hand)?

Is there clear attention to detail? Does the product operate as well as or better than expected?

Does it meet all its functional requirements in a way that is elegant and well thought out?

Ultimately the customer will judge the product and the company by the answer to these “intangible” attributes. ISC strives to achieve this “five star” rating with every customer and every new challenge. If you like the information and think you could use the talent and skills available to you at ISC for your next (or even an existing) product, it is easy to contact us with the information below. We look forward to helping out with your project.

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