In electronics assembly, the materials that bond, protect, and insulate components are just as critical as the solder joints that connect them. Conformal coating, underfill, epoxy, and adhesive dispensing are precision processes where too little material means inadequate protection and too much material risks bridging, contamination, or interference with adjacent components. Dispense process inspection (DPI) has emerged as an essential quality control capability, using 3D measurement to verify that every dispensed material deposit meets specification.
The Challenge: Dispensing Process Variability
Dispensing processes introduce several variables that affect quality:
- Material viscosity changes, Temperature and age affect how conformal coating, underfill, and epoxy flow from the dispense nozzle
- Nozzle wear and clogging, Partially blocked nozzles produce inconsistent deposition patterns
- Board topography variation, Components at different heights affect how dispensed material spreads
- Speed and pressure drift, Process parameters shift over time, impacting deposit volume and placement
- Material waste, Over-dispensing wastes expensive materials and may require rework to remove excess
For conformal coating applications, the stakes are particularly high. Inadequate coating coverage leaves PCBs vulnerable to moisture, chemical contamination, and vibration damage. Automotive ECUs, aerospace flight controls, medical devices, and industrial controllers rely on consistent conformal coating for long-term reliability. A gap in coverage the width of a human hair can be enough to allow corrosion to develop over time.
Underfill dispensing for BGA and CSP packages presents a different challenge. The underfill material must flow completely beneath the component without voids, while forming a consistent fillet around the edges. Too little underfill leaves the solder joints exposed to thermal cycling stress. Too much creates a fillet that interferes with adjacent components or cleaning processes.
How Dispense Process Inspection Works
Dispense process inspection uses 3D measurement technology to evaluate dispensed material deposits. The Neptune C series is a dedicated DPI system that inspects conformal coating, underfill, epoxy, and adhesive deposits using high-resolution 3D imaging.
The system captures key measurements for each dispensed deposit:
- Coverage area, Does the material cover the intended area completely?
- Edge definition, Are the edges clean and within the specified boundary?
- Height and thickness, Is the deposit height within specification?
- Void detection, Are there air bubbles or gaps in the dispensed material?
- Splash and overspray, Has material deposited outside the intended area?
For conformal coating, the Neptune C uses UV illumination combined with RGBW LED lighting to create high-contrast images of the coating material. The AI-powered inspection engine automatically detects bubbles and voids without requiring manual teaching, reducing setup time and improving detection consistency.
For applications requiring thickness measurement of transparent materials, the Neptune C+ uses L.I.F.T. (Laser Interferometry for Fluid Tomography), a proprietary NIR low-coherence interferometry technology. This enables accurate measurement of conformal coating thickness down to 10µm, with an axial resolution of 1µm. The Neptune C+ is the first 3D in-line DPI and thickness measurement solution for transparent material inspection, capable of detecting defects down to 200µm bubbles and 100µm splash marks.
Key Inspection Capabilities
Conformal Coating Inspection
Conformal coating inspection verifies that the protective layer covers all required areas without gaps, bubbles, or thin spots. UV-fluorescent coatings make inspection easier, but clear coatings require L.I.F.T. thickness measurement for accurate verification. The Neptune C+ measures coating thickness across the entire board, flagging areas where the coating is too thin to provide adequate protection or too thick where it may crack under thermal stress.
Underfill Inspection
Underfill inspection focuses on complete capillary flow beneath the component and proper fillet formation around the edges. Voids in the underfill material create stress concentration points that can lead to solder joint cracking under thermal cycling. The Neptune C detects underfill voids using AI-powered inspection that requires no programming, adapting to different board layouts and component geometries automatically.
Epoxy and Adhesive Inspection
Structural adhesives, thermal interface materials, and component bonding adhesives require precise deposition control. The Neptune C verifies deposit location, volume, and geometry, ensuring that adhesive bonds meet strength requirements without material waste or contamination of adjacent areas.
Common Defects Detected by DPI Systems
Understanding the types of defects that dispense process inspection catches is critical for justifying the investment and configuring inspection programs effectively.
Coverage Gaps and Thin Spots
The most common conformal coating defect is incomplete coverage. Material surface tension, board contamination, or component shadow effects can create areas where the coating fails to wet properly. These gaps may be invisible to visual inspection but leave the board vulnerable to moisture ingress and corrosion. The Neptune C detects coverage gaps down to 100µm using AI-powered analysis that compares actual coverage against programmed requirements.
Bubbles and Voids
Air entrapment in dispensed materials creates voids that weaken the protective barrier. In conformal coating, bubbles create pathways for moisture to reach the board surface. In underfill, voids concentrate thermal stress and can lead to solder joint fatigue cracking. The Neptune C detects bubbles down to 200µm automatically without programming, using AI trained on thousands of defect images.
Splash, Overspray, and Contamination
Excess material that deposits outside the intended area can interfere with connectors, test points, heat sinks, or adjacent components. Conformal coating on edge connectors creates electrical contact failures. Underfill that extends beyond the component footprint may interfere with adjacent components or create cleaning challenges. DPI systems detect splash marks as small as 100µm, enabling corrective action before boards progress to downstream processes.
Fillet Geometry Issues
For underfill applications, fillet height and contact angle are critical quality indicators. Insufficient fillet height suggests incomplete capillary flow beneath the component, while excessive fillet height indicates over-dispensing that may bridge to adjacent parts. The 3D measurement capability of Neptune C provides precise fillet geometry data for process control.
Integration with Smart Factory Systems
DPI systems provide their greatest value when integrated into a broader smart factory ecosystem. The KSMART platform connects Neptune DPI systems with SPI, AOI, and other production equipment to create a comprehensive quality picture.
When the Neptune system detects a trend toward insufficient coating thickness on a specific board type, KSMART can alert the dispensing equipment to adjust flow parameters before defects are generated. When material viscosity changes cause edge definition issues, the system flags the condition for preventive maintenance before the problem escalates into a production stoppage.
This closed-loop approach reduces material waste, improves first-pass yield, and provides traceability data for quality management systems. In regulated industries like medical device manufacturing and aerospace, the inspection records from Neptune DPI systems support compliance with ISO 13485, AS9100, and other quality standards.
Selecting a Dispense Process Inspection System
Key considerations when evaluating DPI systems include:
- Material types, Clear, opaque, UV-fluorescent, and transparent materials require different illumination and measurement approaches
- Thickness measurement needs, If coating thickness is critical, a system with integrated thickness measurement like the Neptune C+ is essential
- Board size and throughput, Extended-length boards may require the Neptune USX configuration with capability up to 1,300mm
- AI capabilities, AI-powered void and defect detection reduces programming effort and improves detection consistency
- Integration requirements, Compatibility with KSMART and other factory systems enables closed-loop process control
Koh Young’s Neptune series includes the Neptune C for standard DPI, the Neptune C+ with L.I.F.T. thickness measurement, and the Neptune USX for extended-length board handling. All models feature 12M 15µm cameras with UV-RGBW LED illumination and AI-powered bubble detection that requires no teaching.
Next Steps
Dispense process inspection is becoming a standard quality control requirement for high-reliability electronics manufacturing. If your production process includes conformal coating, underfill, or adhesive dispensing, implementing 3D DPI provides the measurement data needed to ensure process consistency and product reliability.
Interested? Contact Koh Young America to discuss your dispensing inspection requirements and learn how the Neptune series can improve your process quality.
