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Over-Molding and Testing Capabilities

Client Background

A North American manufacturer of heavy-duty industrial sensors faced persistent field failures in their ultrasonic level sensors deployed in outdoor chemical processing plants. The sensors required complete environmental sealing to protect sensitive PCBs from corrosive chemicals, moisture ingress, and mechanical shock—but their existing potting solution was insufficient for the harsh operating environment.

The Challenge

The client’s product demanded:

  • Complete encapsulation of a 6-layer PCB with sensitive analog circuitry

  • Protection against continuous chemical exposure (sulfuric acid, caustic soda)

  • IP68-rated sealing for temporary submersion during washdown cycles

  • Vibration resistance up to 10G for pump-adjacent installations

  • 100% functional testing after encapsulation to verify performance

Their existing potting process using standard epoxy resulted in voids, incomplete coverage, and chemical penetration that led to a 5.2% field failure rate—costly warranty claims and customer dissatisfaction.

Our Approach

Weller’s engineering team developed a comprehensive over-molding and testing solution, combining precision encapsulation with rigorous validation protocols:

  • Material Selection – After evaluating multiple over-molding compounds, we selected a two-part polyurethane system with superior chemical resistance and low viscosity (800 cP) for complete component coverage without voids. The material offered excellent adhesion to FR-4 substrates and a Shore A 85 hardness for vibration dampening.
  • Custom Tooling Design – Precision injection tooling was designed to accommodate the irregular PCB geometry and connector locations. The tooling incorporated strategically placed vents to eliminate air entrapment and ensure complete fill of complex cavities.
  • Controlled Over-Molding Process – A multi-stage injection process was implemented: pre-heating to 60°C to reduce viscosity, controlled injection pressure (200-300 psi) to prevent component displacement, and in-mold curing for 15 minutes before demolding.
  • Post-Mold Curing – Assemblies underwent a two-stage thermal cure: 2 hours at 80°C for initial set, followed by 24 hours at 25°C for full cross-linking, achieving optimal chemical resistance and mechanical properties.
  • 100% Testing Protocol – A comprehensive testing regimen was established:
    • Leak testing – Pressure decay testing at 5 psi to verify seal integrity
    • Dielectric withstand – 2,500 VAC for 5 seconds to confirm insulation
    • Functional verification – Full electrical test of all sensor parameters
    • Environmental stress screening – Thermal cycling (-40°C to +85°C, 50 cycles) and chemical immersion testing

Result

The integrated over-molding and testing approach delivered significant improvements:

MetricBeforeAfter
5.2%
12.3%0.2%
15 kV/mm22 kV/mm

The client deployed over 8,500 encapsulated sensors across chemical processing facilities, with zero failures reported after 18 months of continuous operation. The over-molding process reduced assembly time by 35% compared to their previous manual potting method, and the integrated testing protocol ensured 100% outgoing quality.

Conclusion

This project demonstrates the critical importance of engineered over-molding and comprehensive testing for electronics deployed in harsh environments. By combining precise material selection, custom tooling, controlled process parameters, and rigorous validation testing, Weller enabled our customer to achieve superior environmental protection and eliminate field failures.

For OEMs developing sensors, automotive electronics, medical devices, or any application requiring complete environmental sealing, a well-designed over-molding process can transform product reliability and reduce total cost of ownership.

Industrial sensor over-molding process with precision injection tooling applying polyurethane encapsulant to PCB assembly under controlled pressure and temperature

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