Advanced Underfill Dispensing Capabilities for Complex Semiconductor Applications

Case Study

A semiconductor customer required advanced underfill dispensing solutions to support next-generation packaging with increasingly complex geometries and tighter process constraints. The application environment combined multiple challenges including high aspect ratio structures, interposer layers, miniaturized components, ultra-small gaps, and large device formats. These evolving package designs required precise fluid control to ensure complete underfill coverage, prevent voiding, and maintain mechanical reliability across all device types.

Recommended Dispensing Process:

A MAX-II Series high precision automated dispensing system capable of high accuracy and flexible process control was recommended to address the application challenges.

The proposed solution included:

• System accuracy of ±25 µm or better
• Advanced thermal management with up to three heating zones
• Optional non-contact heating and custom heated fixtures with vacuum capability
• Temperature controls up to 150°C ±3°C
• Integrated FLOware® software for full system and process control
• Closed-loop process control with calibration scale feedback
• UltiPath™ smart path optimization software for efficient dispense sequencing
• Real-time thermal imaging for surface temperature monitoring

This configuration enables consistent process conditions, optimized material flow, and improved throughput across complex assemblies.

Application Challenges

High Aspect Ratio Structures

High aspect ratio geometries were present in the form of tall components with small footprints and elongated rectangular devices. Stacked die configurations further increased process complexity.

To accommodate limited dispense access, tilting of the dispense pump was utilized when traditional top-down dispensing was not feasible. In some configurations, sequential top-down dispensing was possible where sufficient surface area was exposed.

Interposer Layers

Interposer layers introduced additional complexity by acting as interfaces between die and substrate with non-uniform geometries.

These structures:

• Can compensate for mismatched pad-to-bump alignment
• May extend partially or fully beyond component boundaries
• Can be passive or incorporate active circuitry

Their presence requires precise control of underfill flow to ensure full coverage across varying topographies.

Small Component Sizes

Miniaturization required dispensing extremely small volumes with high repeatability.

• Component sizes as small as 3 mm × 3 mm and 4 mm × 4 mm
• Minimum dispensing volume requirements down to nanoliter scale
• The NCM5000 jetting pump (minimum ~2 nL output) was identified as suitable

Ongoing nozzle development with reduced internal diameters supports further reduction in droplet size for future applications.

Small Gaps Under Components

Gap heights as small as 10 µm introduced stringent material and process requirements.

Key considerations included:

• Use of advanced epoxies with sub-micron particle sizes
• Rheology optimized for capillary flow in tight spaces
• Precise control of fluid placement, timing, and flow progression
• Stable process conditions (temperature uniformity, substrate flatness)

Maintaining a consistent flow front was critical to achieving complete and void-free underfill.

Large Component Sizes

Components required higher dispense volumes while maintaining uniform distribution and flow consistency across extended distances.

Process optimization was required to balance volume delivery, flow time, and throughput without compromising quality.

Dispense Pump Options

Two primary dispensing technologies were evaluated for suitability across the range of application requirements.

NCM5000 Non-Contact Jetting Pump

Volumetric PCD Pump

Conclusions

The increasing complexity of semiconductor packaging introduces significant challenges in underfill dispensing, including extreme miniaturization, tighter gaps, and more intricate geometries.

To address these challenges:

• High-precision dispensing systems like the MAX-II series with advanced thermal and process control are essential
• Software-driven optimization (pathing, sequencing, and feedback control) significantly enhances throughput and consistency
• Non-contact jetting technology provides superior performance for small-volume and tight-clearance applications
• Volumetric pumping remains effective for high-volume and larger-scale dispensing requirements

A combination of adaptable hardware and intelligent software is required to ensure reliable, repeatable, and high-quality underfill processes across diverse application conditions.

Final Dispensing Equipment Recommendation