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Managing The Development Of Your Overmolded Cable - Q&A

Steven J Goodman
Written by Steven J Goodman
Posted on November 26, 2019 at 3:28 PM

At the conclusion of our webinar, Managing the Development of Your Overmolded Cable, we had several questions submitted to our presenter, User Interface & Cable Assembly Product Manager Steven J. Goodman. We compiled these into a readable format on our blog.

Q&A From Our Live Cable Webinar

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Download Our Tips on the Pros and Cons of Overmolded Cables

Watch the Recording Below:

Question: Do you offer test capacity for certification of strain relief?

Answer: Yes. The two most common tests for the strain relief portion of our cables are a minimum bend radius test and a flexure or cyclic bending test. These two requirements are typically defined by our customers and are driven by the application. Both tests may be performed on an initial sample during development or implemented on an appropriate quantity during high-rate production. Some requirements drive specialized test setups and fixturing, so it’s best to review what you’re trying to accomplish, and we can recommend the best options for your project.

Question: How about an overmold of an existing cable that needs a LED, resistor, and clear resin (e.g. I want a m12 cable with a power LED and a red LED (1-3) for the output (2-3)?

Answer: Yes. We can overmold with transparent materials. To install an LED, some projects require an intermediary PCB to connect the components and bulk wire, while other projects we can use crimp or solder directly on the LED or resistor’s leg.

Question: How about overmold for mechanical parts (e.g. a schrader-valve to custom fitting)?

Answer: Yes. We can design an overmold tool to seal on the mating surface of your mechanical components. We would need to know more about the item we are sealing on and its respective manufacturing tolerances. If you have a physical part or sample, we would like to use that to develop the tooling and perform some initial runs to prove out the tool.

Question: Are there any overmold resins that are food-contact safe?

Answer: Yes. There are FDA-rated and food-safe compounds. For this, it’s best to provide more information regarding the mechanical performance requirements you need as most of these are specialty materials.

Question: What are the approximate costs for some example cables?

Answer: Cable recurring costs and the tooling non-recurring engineering (NRE) costs vary significantly based on design, conductor count, and cable length. Most of the cost for an overmolded cable is in the connector and bulk cable. The more copper in the cable, the higher the cost. Regarding tooling, the typical cost tooling up a simple cable is between $1,000 and $2,500. As the number of tools increase, so does the cost. Some higher complexity projects require tooling of up to $10,000 or greater. In order to provide pricing information, it’s best to contact the Epec sales team and work toward preparing a custom quotation for your project.

Question: Are there any additional things to keep in mind when overmolding PCBs with components on the board?

Answer: Yes. Since the overmolding operation is performed with heat and pressure, delicate components can be damaged during this operation. For some projects, it’s best to consider an innermold to help protect those delicate components. If required, components can be hand potted to further help protect them before the overmolding operation. Also, the PCB itself can warp during the injection molded operation, so it’s best to plan for additional runs to develop the tooling and prove out the design. Additional gate locations can be added to help uniformly distribute the flow of material within the tool which can help minimize warping and damage to the interior components. Generally, these are items that Epec would take on during development.

Question: How much does a typical overmold cost in terms of piece part price?

Answer: Most of the cost for an overmolded cable is actually in the connector and bulk cable. The overmolded material itself is very inexpensive, and it’s a largely automated process with minimal labor costs. Overmolding a cable is an extremely low-cost and high-reliability solution as long as the tooling NRE is accounted for.

Question: What sort of tolerance range is required for the components to which the overmold is applied?

Answer: The short answer is the tolerance of the component to which we are overmolding is not critical if it is less than +/- 0.010”, but it is important to define this tolerance to a manufacturer like Epec. The overmold tooling will pinch off and seal against your assembly. The overmold tool only physically touches a few locations, usually it’s around bulk cable near the strain relief and a handful of carefully located points on the connector side. The tolerance on the outer diameter (OD) of the cable jacket is typically very tight; the jackets are usually extruded with little variation. This is not a tolerance I would be concerned with. Depending on the material we are overmolding onto, there should be some type of interference fit between the tool and these locations to make sure there is no movement and that we can achieve a seal (we are injecting molten thermoplastic at pressure). If there is a machined part or other surface we are bonding to, I would request that you help specify: 1) the material of this component, 2) the nominal dimension, and 3) tolerance range for that feature. From there, we can develop and prove out the tool to properly function.

Question: Does Epec stock any materials with biocompatibility data or certifications?

Answer: Yes. We use several types of silicone elastomers and thermoplastics that are FDA, food grade, BFR rated, with some materials also having biocompatibility ratings. Some of these materials are manufactured using a compression molding process, not injection molding. These are typically specialty compounds so it would be best to review the application to see if any of our common materials would be appropriate.

Question: Is draft angle a significant consideration for overmolding? What sort of draft angles are required?

Answer: Yes. Without a properly drafted design, the overmolded items may not be able to be removed from the tool. On other instances, it may be difficult to remove your parts from the tool, which can impact yield and costs. This is something that we will review for all designs and remedy in our tooling design. Typically, a draft angle of 2deg is sufficient on most of our designs.

Question: How do you achieve a chemical bond with a cable jacket if waterproofing and high IP rating requirements are in place?

Answer: The best way to achieve an IP67 or IP68 rating is to pair the overmold material with the cable jacket. This helps make certain the overmold material will properly adhere to the parent material. Some overmold materials will list on their data sheets the types of materials that are compatible or materials that should be avoided. I would also recommend that you clearly define that all mating surfaces be cleaned properly before the overmolding operation. Any kind of residue or mold release can decrease this bonds effectiveness.

Question: How do you achieve a high-quality waterproofing for overmolded connectors?

Answer: If you have a strict IP rating, consider an innermold to protect the delicate interior portions of your overmold. This innermold material can help seal against the pins or contacts since this is also a high-risk leak path. Some occasions air or water can wick up the cable conductor, so it’s important to seal the outer jacket and interior conductors. Sometimes soldering the leads before overmolding can help further eliminate ingress up the conductor insulation. To help verify your design throughout production, implement an in-process leak test using air, water, or isopropyl alcohol.

Question: Can overmolding replace the internal seals for connectors' pins to guarantee waterproofing?

Answer: Yes. Overmolding can replace the internal seals for connectors’ pins and guarantee waterproofing. Many automotive connectors come with a connector, pins, and a silicone elastomer seal that is affixed to the opposite side of the connector. This seal can be omitted and replaced with an overmold. Depending on the IP requirement you are trying to achieve, this tactic may be a bit overkill as the standard seal will likely work to at least an IP65/IP66 rating, and possibly higher.

Question: What is the least expensive overmolding material color?

Answer: If you look around where I am right now, most of these cables, their overmold's black. That's typically the most common. Generally, the color itself is not a cost-driver. Black remains the most common color. White is another common color. But we can completely customize the overmold color, whether that's matching a customer's coupon, developing some custom compound based off a pantone color. These are all things we can do. Black or white, is going to be the least expensive, but a custom run is not necessarily expensive. Typically, it's a few hundred dollars to go and colorize some material, but it really all depends.

Question: How do you shield the overmold to meet CISPR requirements?

Answer: When it comes to overmolding cables, most of the time we're dealing with a bulk cable that has some shield within the cross-section, and that's on the bulk cable, but then when you overmold the cable on the connector side, sometimes that shield doesn't always propagate up through the connector. So, it may take some additional activity to go and provide the proper shielding effectiveness on the actual overmolded region.

For some of the high-speed video data cables we develop and manufacturer here… what we try to do is perform the inner mold operation. There's likely some type of PCBA in there, some delicate solder connections, but then we've developed a process where we can actually wrap the inner mold in a copper foil or some other metalized foil, and then from there, place it into the overmold and have at it.

Another option would be a little bit more of an exotic material, but there are compounds where we can embed some type of conductive material within the overmold so that you're actually creating a faraday cage or other shielding property on the outside there. It’s not something I'd recommend unless you're going up with a MIL standard 461 type test.

At a high level, what I'd recommend is you work with us, so we know exactly what radiated emissions test you're trying to accomplish or trying to meet, what your design constraints are, and we can recommend some type of solution, whether it's an internal foil or some conductive material within the overmold to address the shielding requirements there.

Question: What is the highest IP rating you can achieve and how can you guarantee it?

Answer: In order to guarantee some type of IP rating, we need our cable to be mated with our customer's housing and installed in whatever end-user, end-assembly for the system as a whole to work and operate.

That's important because to pass an IP67 or 68 test, you need the cable seated against the bulkhead or wherever it's going and to latch and seat it properly to go and realize that seal. Here at Epec, we can absolutely set up some type of test. We typically want our customers to supply a dummy unit or some other way of mounting or hooking up these units to provide that seal.

It's not something that we can just guarantee at the manufacturing state, but with our experience and design expertise, it's something we can certainly make recommendations to. IP67 is something that we do often. It's pretty common with most of our overmold products, which requires some type of submersion requirement. But for an IP68 test, which is certainly more severe, we recommend that we develop a process and a solution and actually test it either with our customer or at some third-party lab.

Topics: Cable Assemblies

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