Low-pressure molding is a gentle process that you can use to protect delicate electronics. In this guide, we uncover its working and benefits. We will also shed light on its application areas and key considerations when implementing the process for PCB assemblies.
What is Low-Pressure Molding?
Low-pressure molding (LPM) is a protection method that uses injection molding to surround a product with a plastic shell. The plastic prevents ingress, offers mechanical safety, and insulates electrically, among other functions.
The procedure involves melting a thermoplastic or thermosetting material to liquefy it. The melt then goes through an opening and into a mold, filling the cavity and covering the product. After cooling, it hardens around the item.
You can use LPM to encapsulate various items for mechanical, environmental, and other protection needs. One of them is the printed circuit board (PCB). This guide focuses on its use in electronics and PCBs in particular.
How Low-Pressure Molding Works
To grasp how LPM works, we must first understand its parameters. It’s also crucial that you have an idea of the type of materials used and their qualities. Let’s start with the process and its key aspects.
Process Parameters
The process operates at low pressure and temperature. It also utilizes low-viscosity plastics. These are less likely to cause damage. The following are the typical ranges for temperature, pressure, and material viscosity.
- Temperature Range: 180–220°C
- Pressure Level: around 100 PSI
- Material Viscosity: 2,000–10,000 mPa.s
Key Materials
Low-pressure molding materials directly encase the board. You can also use high-viscosity plastics, but these are typically molded over low-viscosity molds to prevent damage.
- Low-Viscosity Thermoplastics: polyolefin, co-polyesters, and polyamide materials
- High-Viscosity Materials: these plastics go over the low-viscosity materials in a two-shot process. They include TPU and TPE.
Resource: https://easyengineering.eu
Low-Pressure Molding Process
Low-pressure molding is a multistep process. Below, we examine each of these steps, from when the molding machine heats the plastic to when the molded board comes out sealed.
Inserting PCB
The operator inserts the circuit board into the mold. The mold is a custom depression designed to fit the specific board. It forms the cavity where the molten material flows into and shapes the final product.
Material Injection
The material melts in the molding machine. It then goes through a small opening to reach the mold cavity, flowing through gates and runners to ensure uniformity. The pressure must also remain within safe limits.
Encapsulation
The molten material flows over the circuit board, covering its products. The melt’s temperature must not be too high to cause damage, especially since the process must be safe on such PCBs.
Cooling and Ejection
The material cools, turning into a solid. The result is a hardened shell around the board. After cooling and solidification, the encapsulated board is ready for ejection. The operator takes the PCB out, or the process is automated.
Device Testing
The overmolded circuit board goes through a quality control process where experts test its operation. It must work correctly and reliably to indicate a successful molding process. It means the melt did not damage the board and components.
Resource: https://www.mdpi.com
Why Use Low-Pressure Molding for PCB Protection
Various reasons explain why low-pressure overmolding is the preferred protection method in electronics. The benefits when compared to high-pressure molding include the following:
Gentle Encapsulation
The molding pressure and temperature levels are low enough to be safe on electronic circuit boards. The low-viscosity material will also not cause mechanical stress, making the process compatible with fragile components.
Reduced Material Use
The low injection pressure reduces material consumption when using the method. That makes LPM a more sustainable process. Most LPM materials are also environmentally friendly, adding to the sustainability benefits.
Cost-Effectiveness
The reduced material needs and low wastage make LPM more cost-effective than HPM. You spend less on material and energy to protect your board, making the method cheaper. It also uses shorter cycle times, reducing the time spent molding.
Enhanced Versatility
You can use LPM for a broad range of applications, given its compatibility with different materials and board requirements. In other words, you have more options when using the low-pressure process to seal electronics.
Low-Pressure Molding Applications in Electronics
Low-pressure molding suits an array of applications in electronics, given its many benefits and material versatility. The following are examples of uses in various application boards.
- Medical devices
- Automotive electronics
- Avionics
- Industrial Electronics
In these uses, the encapsulation helps prevent moisture, dust, and other environmental factors from damaging the PCB. It also electrically and mechanically safeguards the board, making it safer while also extending its lifespan.
Resource: https://semanticscholar.org
Key Considerations When Using Low-Pressure Molding
Anyone considering LPM for circuit board protection must understand how it encapsulates electronics and why. They must also have an idea of the materials used, such as thermoplastics and thermosets. The following are key factors to consider.
Material Selection
Choose molding materials based on the PCB type and application. The material must be compatible with the components. It should also be of high quality to withstand the board’s usage conditions by resisting heat, chemicals, vibrations, etc.
Polyamide and polyolefin are good candidates, as we saw earlier. They are low-viscosity materials and widely used in many LPM processes due to their favorable sealing and durability qualities.
Mold Design
Ensure the mold design is suitable for the process. It should offer uniform mold thickness. It should also let gases escape and prevent voids. Another requirement is allowing proper material flow and solidification for a structurally sound seal.
Machine Settings
Precision is crucial when using a low-pressure molding system. The molding equipment must accurately control temperature and pressure levels. Other parameters include the injection speed, shot size, and cooling time. It ensures a high-quality overmold.
Conclusion
Low-pressure molding allows you to seal and protect PCBs with sensitive components. The low pressure and temperature levels also reduce material wastage, making the process sustainable and cost-effective, among other benefits.
At Venture, we understand the need for LPM in PCB sealing. We offer various material options to protect your PCB based on your application requirements. Talk to us now. Our engineers will advise you on the best path to take.
