PCB overmolding encases the board, offering benefits that range from electrical insulation to environmental protection. The technique is crucial in electronics, especially if the application exposes the PCB to damage. Below, we explain how it works and its benefits.
What is PCB Overmolding?
Overmolding means enveloping an assembled circuit board in rubber or plastic using the injection molding process. It involves placing the PCBA in a custom mold and filling the cavity with molten material.
Upon cooling, the material forms a solid protective shell around the board. Customizing the mold allows the user to personalize the final product in terms of design and shape.
On the other hand, the material choice determines protection capabilities and aesthetics. That way, you can tailor the overmold to match your specific application.
Different types of printed circuit boards can benefit from overmolding. They include those used in harsh environments, such as automotive, medical, avionics, and some consumer products.
PCB Overmolding Techniques
The overmolding is either a low-pressure or high-pressure process. The two methods differ in their execution and the type of materials they use. They also produce varying results, affecting your product’s features and budget.
Low-Pressure Overmolding
The low-pressure procedure uses low injection temperatures (180-220°C) and pressures (100 PSI). It mainly suits less-viscous materials, which require less force to move into the mold.
The reduced heat and pressure suits circuit boards with delicate electronic components since it won’t damage them. Low-pressure molding is also more cost-effective.
High-Pressure Overmolding
This method involves high material injection pressure (25, 000 PSI) and temperatures (185-300°C). Unlike the low-pressure method, it typically fits viscous materials.
High-pressure molding doesn’t suit PCBs with fragile parts, as the elevated pressures can damage them and ruin entire assemblies. It also costs more, increasing the circuit board’s protection expenses.
Resource: https://hackaday.com
Why Overmold a PCB?
Overmolding offers several key advantages that justify the process, despite the increased cost. It protects the board against environmental factors, ensuring its reliability and improving its lifespan. That is despite the increased cost. The benefits of overmolding printed circuit boards include those discussed below.
Environmental Protection
It seals the circuit board inside a shield, offering additional protection. The shield prevents damage by keeping out dust, moisture, chemicals, etc.
In other words, it extends the board’s lifespan by preventing ingress. The process usually achieves IP ratings of up to IP 69, depending on the material type and other features.
Mechanical Protection
It reduces the chances of damage during use in harsh conditions. For instance, the material improves the pull strength and provides strain relief. This protection is crucial in high-traffic areas of the board, such as around or near connectors.
Flexible materials protect against vibration damage. This protection is critical in specific settings, such as automotive and industrial application circuit boards.
Aesthetic Appeal
Bare PCB assemblies are not visually pleasing on consumer products and in various other applications. That could affect the product’s acceptability on the market, in addition to exposing the board to damage.
The overmold helps improve the look by covering the exposed component, making the device sleek and visually attractive. It also allows preferred colors, designs, and shapes.
Electrical Insulation
The overmolding material is non-conductive. It insulates the PCB, preventing electrical incidents such as arcing and short-circuits. The insulation also makes the board safer for users to handle.
Enhanced Customization
Overmolding circuit boards allows for many customization options to improve various aspects, such as visual look and ergonomics. For instance, you can use appealing colors and finishes or introduce handy grips to make the product more usable.
PCB Overmolding Material Types and Their Qualities
The material used to overmold your PCB must be the right type based on its properties and other considerations, such as cost. Let’s examine each factor below.
Overmolding Materials
PCB overmolding materials include thermoplastics and thermosetting resins. You can remold thermoplastics, while thermosets harden permanently. Here is more about the two groups, including examples of each.
- Thermoplastics – TPU, TPE, PVC, polycarbonate, ABS, polyamide (nylon)
- Thermosets – epoxy, PU, silicone, phenolic resin
Key Material Qualities
The material’s qualities determine its suitability for use. The following are the key qualities when selecting the best option for your board.
- Thermal properties – for high-pressure molding high-temperature applications
- Flexibility – for wearable devices
- Chemical resistance – for harsh environments
- Biocompatibility – for medical electronic devices
- UV stability – for applications that expose the board to light
- Color compatibility – for aesthetics
- Optical clarity – for transparent molds, such as those used to house LED electronics
- Cost – for budget requirements and PCB or application type
Resource: https://www.sciencedirect.com
PCB Overmolding Process
The procedure requires an injection molding machine to heat the plastic and force it into a mold. The following steps explain how that works, from the beginning to the end.
Initial Preparations
Preparing the PCB for the process involves removing contaminants from its surface and masking delicate components. It also includes configuring molding machines to ensure the correct molding temperature and pressure.
Overmolding Steps
The material undergoes gradual heating in the injection molding machine. The heat turns it into a melt before being injected into the mold. The mold contains the PCB, and the material cools to solidify around it.
The molding is either a low-pressure or high-pressure process. A low-pressure molding system reduces the injection speed but protects components, making it the preferred method for electronic boards.
Post Molding Procedures
Post molding steps include inspecting the finished product to detect flaws and trimming to remove excess material. Finally, the overmolded board undergoes testing to confirm its functionality.
Resource: https://easyengineering.eu
PCB Overmolding Applications
Overmolding offers various benefits. The types of circuit boards that can benefit from the technique are diverse. The following are examples of such applications.
- Automotive Electronics – sensors, control modules, lighting devices
- Consumer products – ear buds, wearable tech, outdoor gadgets
- Medical devices – health monitoring products, diagnostic equipment, implants
- LED Applications – IP-rated LED products for outdoor use like lighting, decoration, and signage
- Industrial Systems – rugged sensors, control modules, and other devices for demanding environments
Best Practices for Overmolding PCB Boards
Design Considerations – the design must favor overmolding. Best practices include minimizing component height, strategic part placement, and optimized spacing.
PCB Cleanliness – The board must be thoroughly cleaned to remove any contaminants before molding. Residue can affect the adhesion and quality of the final seal, causing problems, such as air pockets and structural integrity issues.
Material Selection – the material must match application requirements: epoxy and silicone for high temperatures, TPE and TPU for flexibility, and polycarbonate or ABS for rigidity.
Process Control – choose a molding method that will not damage the PCB and its components. Determine your board’s thermal limits. The temperatures must be low enough so it doesn’t affect sensitive devices.
Budget Considerations – the material’s price must match budget estimates based on the specific application. Select a cost-effective option if you want a material that will keep the board costs within limits.
Conclusion
PCB overmolding is essential in many electronic applications. It involves covering a PCBA with an insulating material, such as plastic. The type of material to use depends on the desired protection level and board flexibility needs.
Venture offers a broad range of overmolding options for PCB protection. We can customize materials and mold thickness to match your application’s mechanical, chemical, and appearance needs. Get in touch with us now for more information concerning our PCB manufacturing and overmolding services.
