Low pressure molding (LPM) is an encapsulation process in which a hot-melt thermoplastic adhesive is injected at low pressure — typically between 1.5 and 40 bar — into a mold cavity containing the electronic assembly. The material flows around the components, fills gaps, and solidifies within seconds, forming a seamless, waterproof shell that conforms precisely to the board geometry. Because the injection pressure is low and the material temperature is moderate, even fragile sensors, fine-pitch connectors, and bare chips can be overmolded without mechanical damage.
The result is a single solid part in which the circuit board is fully enclosed. There is no separate housing to assemble, no liquid resin to cure in an oven, and no masking step to remove afterward. For a manufacturer running low pressure molding for sensitive electronics, the entire protection step can be completed in three movements: load the board, inject, and demold. Compare that to potting, which may require mold preparation, housing assembly, dispensing, vacuum settling, and an extended oven cure — often a full shift of elapsed time before the part is ready to test.
Each protection method has a legitimate role, but they are not interchangeable. Choosing the wrong one is a common source of avoidable field returns.
| Factor | Conformal Coating | Low Pressure Molding | Potting |
|---|---|---|---|
| Typical protection | Thin film against moisture, dust, mild chemicals | Full encapsulation, waterproof to IP67/IP69, strain relief | Full encapsulation, thick bulk protection |
| Process steps | Masking, spray/dip, cure, demask | Load, inject, demold (3 steps) | Housing prep, dispense, vacuum, oven cure (up to 8 steps) |
| Cycle time per part | Minutes to hours (cure dependent) | Seconds to tens of seconds | Hours (long cure) |
| Weight added | Negligible | Low — skylining possible | High — fills entire cavity |
| Reworkability | Limited (material dependent) | Good — thermoplastic can be reworked | Poor — cured resin is permanent |
| Best fit | General indoor electronics, cost-sensitive boards | Sensors, connectors, wearables, automotive, medical | Heavy industrial, high-voltage, bulk thermal mass |
Conformal coating remains the right call for boards that face humidity and dust but not direct liquid immersion. A well-controlled conformal coating line, with selective spraying, controlled thickness, and proper baking, will protect the vast majority of indoor and semi-outdoor assemblies at the lowest cost per board. LPM becomes the better choice when the product must survive liquid exposure, mechanical strain on cable exits, or repeated thermal shock that would eventually crack a thin coating film.
Low pressure molding is not a niche technique. It is used across the same industries that drive the majority of PCBA volume today, and the protection requirements in each sector push the technology in slightly different directions.
Protection is only one stage in a longer chain. A board that is beautifully overmolded but built on a poorly controlled SMT line, or sourced from unverified components, will still fail. This is why the value of LPM is multiplied when it is performed by a partner who also controls the upstream stages — from bare-board fabrication through component sourcing, assembly, and testing.
Consider the sequence a board follows at a vertically integrated manufacturer. It starts with PCB fabrication, where material selection, copper thickness, and impedance control set the foundation. Components are then sourced through a managed electronic component management system that verifies authorized-channel sourcing, performs incoming inspection, and controls warehousing under anti-static and temperature-regulated conditions. The board then moves through SMT placement, DIP through-hole soldering, and conformal coating (where specified), before arriving at the LPM station for encapsulation.
After molding, the part is not finished until it passes a structured pcba testing process that includes visual inspection, AOI, X-ray, functional testing, and where required, thermal cycling and IP-rating validation. When all of these stages sit under one roof, the feedback loop is short: a coating defect found in testing can be traced back to spray parameters within hours, not weeks. A solder defect under an overmolded connector can be caught by X-ray before the mold is even closed.
Not every factory that owns a molding machine can deliver production-grade encapsulation. When evaluating a partner for OEM PCBA work that includes low pressure molding, several capabilities matter more than the machine count on the shop floor.
For engineering teams deciding between coating, molding, and potting on a new product, the decision can be reduced to a few questions. Will the product face liquid immersion or only humidity? If only humidity, conformal coating is sufficient and cheaper. Will it face mechanical strain on wires or connectors? If yes, LPM provides strain relief that coating cannot. Is weight critical, as in wearables or drones? LPM with skylining keeps mass low while still encapsulating. Is the part a high-voltage power module needing bulk thermal mass? Potting may still be the right answer despite its longer cycle.
The most cost-effective approach is often a hybrid: conformal coating on the main board area for moisture protection, combined with low pressure molding specifically on connector zones, sensor modules, or cable exits where strain and liquid ingress are the real risks. A partner who runs both processes on the same production line can deliver this combination without shipping boards between vendors.
Farway Electronic operates a 2,000-square-metre production facility in LongGang, Shenzhen, with two SMT lines, two DIP lines, a conformal coating line, four low pressure molding machines, and two finished-product assembly lines under one roof. That layout is deliberate: it allows oem pcba manufacturing to move from bare board to overmolded, tested, and box-built product without leaving the factory.
The company holds ISO 9001, ISO 13485, IATF 16949, and ISO 14001 certifications, covering quality, medical, automotive, and environmental management respectively. Its testing capability spans SPI, AOI, X-ray, ICT, FCT, thermal imaging, and high/low-temperature reliability testing, with a one-year free-repair commitment for non-external manufacturing defects. For customers in automotive, medical, security, new energy, and communications, this means the LPM stage is backed by the same engineering team that designed the assembly process upstream — not handed off to a third-party molder with no visibility into the rest of the build.
If your next PCBA project needs waterproofing, strain relief, or field-grade encapsulation, the worst time to decide on protection is after the first field failure. Farway Electronic's engineering team can review your design, recommend whether conformal coating, low pressure molding, or a hybrid approach fits your environment, and quote the full build from PCB through tested, overmolded assembly. Contact sales@farway.hk or visit www.farway.hk to start the conversation.
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