When a sensor fails after one rainy season, or a battery connector corrodes inside a humid enclosure, the root cause is rarely the circuit design itself. It is the protection layer, or the lack of one. Low pressure molding has become the go-to encapsulation method for manufacturers who need genuine waterproofing without damaging fragile components, and for good reason: it seals electronics in a solid, thermoplastic shell in minutes, not hours. This guide breaks down how the process works, where it fits alongside other protection methods, and what to look for when choosing a manufacturing partner in Asia.
What Is Low Pressure Molding?
Low pressure molding (LPM) is an encapsulation process that injects hot-melt polyamide or polyolefin adhesive into a mold cavity at relatively low pressure, typically between 2 and 60 bar, and at temperatures around 180 to 220 degrees Celsius. The material flows gently around sensitive electronic components, connectors, and wire harnesses, then cools and solidifies into a seamless protective shell within seconds. Unlike traditional high-pressure injection molding, the low pressure means delicate PCBA assemblies, solder joints, and thin-gauge wires are not stressed or displaced during encapsulation.
The technology originated in European automotive manufacturing in the 1980s as a faster, cleaner alternative to potting with epoxy resins. Today it is widely used across low pressure molding for waterproof electronics, medical devices, LED lighting, sensor modules, battery packs, and connector overmolding. The result is a component that meets IP67 or even IP68 ingress protection ratings while remaining reworkable, lightweight, and free of the long curing cycles that potting compounds demand.
Low Pressure Molding vs. Conformal Coating vs. Potting
Choosing the right protection method depends on the environment the product will face, the level of sealing required, and the production volume. The three most common approaches are not interchangeable, and understanding the trade-offs prevents costly over-engineering or premature field failures.
| Method |
Protection Level |
Key Characteristics |
| Conformal Coating |
Light to medium moisture, dust, chemicals |
Thin film (25 to 75 microns) applied by spraying or dipping. Good for dense PCBAs. Does not achieve full waterproofing. |
| Potting |
Full encapsulation, heavy mechanical protection |
Liquid resin poured into a shell and cured. Long cycle times, heavy weight, difficult to rework. |
| Low Pressure Molding |
Full encapsulation, IP67/IP68 waterproofing |
Solid thermoplastic shell formed in seconds. Lightweight, reworkable, gentle on fragile components. |
For many products the two methods are complementary rather than competing. A board may receive conformal coating to protect individual traces and solder pads from condensation and dust, and then a low pressure molding shell around a connector or sensor tip to provide true waterproof sealing at the cable entry point. Understanding where each method adds value is the difference between a reliable product and an overbuilt one.
Where Low Pressure Molding Delivers the Most Value
LPM shines in applications where a bare PCB or a coated board alone cannot survive the operating environment. The following are the most common use cases where manufacturers choose encapsulation over coating:
Automotive Electronics
Window-lifter controllers, anti-pinch modules, and in-cabin sensors face temperature swings, vibration, and moisture. LPM seals connectors and PCBs to meet automotive reliability standards.
Medical Sensors
Disposable and reusable medical sensors require biocompatible sealing, sterilization resistance, and IP-rated waterproofing for bodily fluid exposure.
LED Lighting
Outdoor and underwater LED drivers need protection against humidity, salt spray, and thermal cycling without adding excessive weight to the fixture.
Battery & Power Modules
Mobile-phone and power-tool battery packs use LPM to seal cell connectors and protection circuits against moisture and mechanical shock.
Connector Harnesses
Cable-to-board transitions are the weakest link for water ingress. Overmolding at the junction creates a strain relief and a watertight seal in one step.
Industrial Sensors
Factory-floor sensors for pressure, flow, and temperature operate in oil, coolant, and washdown environments where bare electronics fail quickly.
The Manufacturing Process: From Bare Board to Sealed Module
A well-executed low pressure molding project is not just about the molding step. It is an integrated chain that begins with a reliable PCBA and ends with a tested, packaged product. At Farway Electronic in Shenzhen, that chain is handled under one roof, which reduces handoff risk and shortens lead times.
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PCB fabrication and SMT assembly. Rigid, flexible, and rigid-flex boards from 1 to 32 layers are produced and populated using Yamaha placement machines capable of handling 01005 components and 0.2 mm BGA pitch. This smt pcb assembly shenzhen capability ensures the board entering the molding stage is already soldered and inspected to IPC-A-610 standards.
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DIP and through-hole soldering. Connectors, headers, and larger through-hole parts are wave-soldered on dedicated DIP lines, then visually inspected and functionally tested before encapsulation.
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Conformal coating (optional). Where the design calls for layered protection, an automated conformal coating line applies acrylic, silicone, or polyurethane films with selective masking and double-sided spraying for boards up to 550 mm by 470 mm.
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Low pressure injection molding. The assembled and tested PCBA is placed in a custom mold, and hot-melt adhesive is injected at low pressure to form a solid, waterproof shell. Farway operates four low-pressure injection molding machines, supporting medical sensors, automotive modules, LED drivers, battery packs, and connector overmolding.
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Testing and inspection. Encapsulated units undergo AOI, X-ray, ICT, FCT, thermal imaging, and high/low-temperature reliability testing to verify that the seal is intact and the circuit functions as specified.
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Finished product assembly. The sealed module is integrated into its enclosure with wiring harnesses, HMI panels, and connectors, then packaged with barcode traceability and anti-static protection.
Why Integration Matters
When PCB fabrication, SMT, DIP, coating, molding, testing, and final assembly are handled by separate vendors, each handoff introduces delay, miscommunication, and quality risk. A single partner that controls the entire chain, from Gerber file to shipped box, can shorten development cycles and maintain consistent quality standards across every step.
Quality Systems and Certifications
Waterproofing claims mean nothing without the quality systems to back them up. Manufacturers serving automotive, medical, and industrial markets should hold certifications that match the end-product requirements. Farway's facility in LongGang, Shenzhen operates under four management-system certifications: ISO 9001 for quality management, ISO 13485 for medical devices, IATF 16949 for automotive, and ISO 14001 for environmental management. Product-level certifications in scope include UL, RoHS, SGS, and REACH, and assembly work follows IPC-A-610 standards.
For automotive projects specifically, IATF 16949 compliance is not optional. It is a baseline requirement for any supplier entering the global automotive electronics supply chain, covering everything from risk management and traceability to defect prevention and continuous improvement. Choosing a partner who already holds this certification eliminates a major qualification hurdle.
What to Evaluate When Choosing a Manufacturing Partner
Not every factory that owns a low pressure molding machine can deliver reliable, waterproof electronics at scale. When shortlisting partners in China or elsewhere in Asia, evaluate the following criteria before committing to a production run:
- End-to-end capability: Does the partner handle SMT, DIP, coating, molding, testing, and finished product assembly service china in-house, or will parts be subcontracted?
- Relevant certifications: Are ISO 9001, ISO 13485, IATF 16949, and ISO 14001 all current and verifiable?
- Testing depth: Does the factory perform AOI, X-ray, ICT, FCT, and environmental testing, or only visual inspection?
- Material sourcing: Does the partner work with authorized distributors for both electronic components and molding compounds, with incoming inspection and ERP-controlled warehousing?
- Prototyping flexibility: Can the factory support prototype quantities from a single piece, then scale to medium and high-volume production without retooling?
- Communication and lead time: Is quotation fast, and is there an engineering team that can review DFM feedback before tooling investment?
Common Pitfalls in Low Pressure Molding Projects
Even with the right partner, projects can go off track. The following issues appear repeatedly in low pressure molding programs, and each is preventable with early engineering involvement:
- Inadequate DFM review: Sharp corners, unsupported components, and insufficient draft angles cause mold filling problems and stress concentration. A DFM review before tooling cuts development time.
- Wrong material selection: Polyamide and polyolefin adhesives have different hardness, temperature resistance, and chemical resistance. Choosing based on price rather than application requirements leads to field failures.
- Skipping pre-molding testing: Molding over an untested PCBA locks defects inside a solid shell. Always perform ICT and FCT before encapsulation.
- Ignoring IP rating verification: A visually sealed part is not necessarily waterproof. Leak testing and thermal cycling should confirm the seal meets the specified IP rating.
Ready to Waterproof Your Next Product?
Farway Electronic Co., Limited has served more than 100 industry customers across over 20 countries and regions with one-stop electronics manufacturing, from PCB fabrication and
oem pcba manufacturing through conformal coating, low pressure injection molding, PCBA testing, and finished product assembly. Whether you are prototyping a medical sensor or scaling an automotive control module to mass production, the engineering team in Shenzhen can review your design, recommend the right protection strategy, and deliver sealed, tested, and packaged units. Contact
sales@farway.hk or call
181 2472 7402 to discuss your project requirements.
