How To Mold/Overmold Plastic Onto a PCB

Watching a strain relief being molded onto one end of a PCB assembly using a high pressure mold and PVC looks like something out of a sci-fi movie (seriously, check out the video below). However, this process adds so much durability and protection to the assembly below and can be customized perfectly to whatever the intended application may be.

That’s why we’re dedicating this entire LiveWire post just for molding and overmolding onto PCBs and how investing in this process can add big-time strength and resiliency to your next custom cable assembly design project. 

What is a Printed Circuit Board (PCB)?

PCBs are the tiny workhorses that really make modern technology possible. It used to be that wires were connected point to point. This was tedious both for production and maintenance. Hence, the concept of printing circuits on a board. It all starts with a simply conductive sheet like copper. Usually, a sandwich insulative layer gives support to the conductive layer. Sheets get drilled with registration holes for proper alignment. CAD designs produce detailed 3D models that give the drilling machine the information it needs to drill proper hole locations. 

Etching in an alkaline solution helps produce the required tracing of copper. Usually a UV light places the mask on the copper plate and can be done in bulk. Copper traces are always checked for quality usually with an optical testing machine that watches for damage or short circuits. A solder mask coating gives the characteristic green color and provides insulation and protection. A silkscreen provides markings, symbols, or logos straight to the PCB. At this point, components can then be soldered onto the PCB. A flying probe test can be used to test connectivity. 

PCBs can either employ through hole technology or, more lately, surface mount technology, depending on the needs of the project. 

For that Matter, What is Overmolding?

Now that you’ve got a better handle on PCBs, let’s cover what overmolding is. Overmolding is a process utilizing insert molding and/or injection molding in order to organize and protect wires and connectors. When designing a cable overmold, the cable assembly components getting this upgrade are placed in a mold where they are then covered with molten plastic material with injection. This process provides the perfect solution for so many different applications requiring sealed wires and connectors, especially when these are going to be facing extreme environments. 

Consider a satellite being launched into space, or a PCB inside a hot industrial control panel, or perhaps where saltwater exposure is expected. Without a solid overmold, components can quickly be degraded by their environment and the processes the assemblies are being subjected to. 

Overmolding can also aid in protecting sensitive components from interference in the form of electromagnetic and radio frequency interference (EMI and RFI, respectively). Adding mechanical strength, durability, and flexibility overmolding has many benefits but it can also “clean up” a given component for better aesthetics and ease of maintenance down the road.

So, What is a Mold?

A mold used in PCB overmolding is a key part of our tooling inventory. After decades as a leading custom cable manufacturer, our tool crib currently consists of well over 5,000 existing tools, overmolds, connectors, terminations, and other components to pull off the perfect assembly. However, even with such a vast tool crib of things like molds at our disposal, with any sort of custom work, so comes the need for custom tools made just for the task at hand. This is where working with a custom cable manufacturer can really pay huge dividends over off-the-shelf assemblies. 

Our team truly excels at the custom design process and in fact, we design over 70% of the systems we produce. We’re basically a design shop that happens to provide cutting-edge volume manufacturing capabilities as a side hustle. All of that said, molds can be quite simple or they can be incredibly complex. They can also be made with different metals or may require additional finishing techniques to pull off the perfect final product. 

A hardened steel mold is one of the most common since these are relatively inexpensive because of their increased lifespans and suitability on volume production runs. Another key aspect of working with a custom cable manufacturer lies in the ability to prototype. We’ll typically use aluminum cast dies in the prototyping process to produce a viable and cost-effective way of testing different processes and materials to make a certain version of the same design. 

Once we zero in on the most efficient amalgamation during prototyping, we’re lightyears ahead with a proven design and pre-mapped production process. This helps ensure quality and delivers far more consistent results to our customers.

Benefits of Employing Molding and Overmolding with PCBs

When you look to increase the stoutness of a PCB component with overmolding, you’re going to get a more durable and better performing system than one that doesn’t have it. But, obviously there is a cost in adding on another level of protection, so how do you know if it’s worth the investment? Well, let’s look over a couple of the benefits of overmolding, including:

  • Stronger. Finding a big increase to flexural strength levels. If you zero in on high-traffic areas like cable exits, the addition of flexural strength means these connection points can take more wear and tear and keep on operating. 
  • Tougher. A wall of protection around the components themselves. You will find that extreme temps, water, abrasion, impacts, and other forces are no match for a high-quality overmold. 
  • Better security. Providing an additional layer of protection against even deliberate outside force, an overmold is like your PCBs personal bodyguard.
  • Better performance. Gaining better pull strength and strain relief performance metrics. 
  • Better protection. Sealing off components from caustic liquids such as oil or saltwater. 
  • Better looking. Making a more aesthetically-pleasing component. Looks sell, even with PCBs and cable assemblies. Making a final product that looks better, is easier to integrate, and easier to maintain, overmolding gives a big boost in the aesthetics department.

Meridian’s design engineers know their ways around special considerations like overmolding and can help you pinpoint when the investment would help produce the greatest return during the project. Schedule your project kick-off meeting now and get a dedicated professional personally who is there to expertly guide your project to completion. 

Customizing Overmolds

The benefits of overmolds continue in their ability to be highly customized according to the unique parameters set by our clients. Customizing the overmolds with PCBs affords many different opportunities for ratcheting up the “wow factor” including:

  • Setting different colors for better overall wire management.
  • Printing corporate logos, names, or other forms of branded messaging.
  • Providing places to integrate attachment hardware such as a flange.
  • Giving options for exit point angles, such as a right angle, to meet the needs of the project.
  • Using different overmold materials such as PVC or thermoplastics. 
  • Getting to employ different machines we have like the venerable Low Pressure Molding System (LPMS) to provide the most cost-effective solution. 

Our team is made up of masters of the budget. We work within a set of given parameters to provide the best possible solution. Projects completed on time and on budget that are mindfully created to solve the task at hand are simply what we do.

A Closer Look at the Process for Overmolding

Injection molding machines are the true workhorses pulling off this crucial bit of cable engineering. Our machines are able to reach high levels of pressure (or low as the needs of the project dictate) and push whatever molten material is desired into the molds. Thermoplastic polyurethane is commonly used as an injectable material for the mold. 

  1. The Machines: Which Injection Molding Machine to Use? 

Injection molding machines are all about tonnage. Tonnage is how much force each machine uses in order to suspend a molten resin within the mold. If a mold is huge, more force is required which is why having the right injection molding machine is crucial for success. 

  1. The Materials: Choosing Which Materials Are Best for Overmolding

Next up, there are an almost endless amount of different materials out there which produce different final results. One may provide better rigidity, another more flexibility—it all comes down to the needs of the project. However, two of the most common overmold materials include polyvinyl chloride (PVC) and thermoplastic polyurethane (TPU). PCV is common because it’s economical and does a great job at adding strength and moisture-proofing.

  1. The Process: Injection Molding at Its Finest

Once the material is chosen, the hopper on the injection molding machine is filled and an injection screw pumps it into a mold. The barrel actually heats the material into the tooled mold and continues to add pressure until cooled for solidification to occur.

Getting a Mold/Overmolded Plastic On Your PCB

Overmolding your PCB components can really increase the stoutness of the overall system. If you’re not sure where to begin, simply contact our team and we’ll help walk you through all your options.