Semiconductor Die Capillary Structures for Faster Underfill Flow
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Solution Overview
Problem
Conventional direct chip attachment technologies face limitations in throughput due to the flow rate of underfill material, which can lead to thermomechanical and chemical damage, as well as shear stress caused by mismatched thermal expansion between semiconductor dies and substrates, and often result in non-uniform gaps and potential electrical issues.
Innovation Solution
The implementation of capillary flow structures on the semiconductor die or substrate, which enhance the flow rate of underfill material by adjusting the geometry and material properties of these structures to increase capillary action, ensuring uniform spacing and improved adhesion between the die and substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional direct chip attachment technology is used with standard underfill flow rate, then the manufacturing process is simple, but the throughput is limited and underfilling time is excessive
Solution Approach 1:
The patent modifies the physical parameters of the underfill material by adjusting its viscosity and surface tension properties. Specifically, the underfill composition includes resins with controlled molecular weight, curing agents, and additives that modify capillary pressure. These parameter changes enable faster capillary flow through the gap while maintaining proper adhesion and stress compensation functions.
Solution Approach 2:
The patent utilizes the gap between the semiconductor die and substrate as a porous-like flow path, and introduces flow enhancement structures such as textured surfaces or micro-channels on the die or substrate surface. These structures increase the effective surface area and create capillary channels that accelerate underfill material flow, thereby reducing underfilling time while improving throughput.
2Productivity
If underfill material flows slowly through the gap, then the gap remains uniform, but the throughput of COB manufacturing processes is limited
Solution Approach 1:
The patent changes the rheological parameters of the underfill material, specifically reducing viscosity and optimizing surface tension to enhance capillary flow velocity. The composition includes low-viscosity resins and flow modifiers that enable faster material movement through the gap without compromising the uniformity of gap filling or the protective functions of the underfill.
Solution Approach 2:
The patent employs a two-stage underfill process: first, a fast-flow underfill material is applied to quickly fill the gap and establish basic adhesion; second, a slower-curing underfill is applied to complete the filling and provide long-term stress compensation. This periodic action with different flow rates optimizes both throughput and gap uniformity.
3Reliability
If the underfill material is applied to protect active surface and bumps, then thermomechanical and chemical damage is reduced, but the flow rate limitations cause extended processing time
Solution Approach 1:
The patent modifies the chemical composition and physical parameters of the underfill material to achieve both fast flow and protective functions. The formulation includes adhesion promoters, stress-compensating agents, and curing modifiers that enable the material to flow quickly while maintaining its protective role in preventing thermomechanical and chemical damage to the active surface and bumps.
Solution Approach 2:
The patent applies a preliminary fast-flow underfill layer first to quickly establish basic protection and adhesion, reducing the critical exposure time of the active surface. Then, a second underfill layer with enhanced protective properties is applied to complete the protection. This preliminary action sequence reduces overall processing time while maintaining comprehensive protection.
4Reliability
If conventional underfill material is used, then the process is simple, but shear stress from mismatched thermal expansion is not adequately reduced
Solution Approach 1:
The patent uses composite underfill materials combining multiple resin systems, curing agents, and functional additives in specific ratios. This composite formulation provides enhanced stress compensation properties by incorporating materials with different thermal expansion characteristics, flexible polymers for stress absorption, and adhesion promoters for strong bonding. The complexity of composition is justified by the significant improvement in shear stress reduction and device reliability.
Solution Approach 2:
The patent adjusts the chemical and physical parameters of the underfill material, including molecular weight distribution, crosslink density, glass transition temperature, and thermal expansion coefficient. These parameter changes enable the underfill to better match the thermal expansion properties of the die and substrate, thereby reducing shear stress from thermal cycling while maintaining processability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution increases the flow rate of underfill material, reduces the time required for underfilling, maintains uniform spacing between the die and substrate, and enhances the yield by providing a consistent mechanical grip, thus addressing the limitations of conventional methods.
Implementation Method 1
capillary flow structures on the semiconductor die or substrate, which enhance the flow rate of underfill material by adjusting the geometry and material properties of these structures to increase capillary action
Data Source
AI summary
A semiconductor device having a capillary flow structure for a direct chip attachment is provided herein. The semiconductor device generally includes a substrate and a semiconductor die having a conductive pillar electrically coupled to the substrate. The front side of the semiconductor die may be spaced a distance apart from the substrate forming a gap. The semiconductor device further includes first and second elongate capillary flow structures projecting from the front side of the semiconductor die at least partially extending toward the substrate. The first and second elongate capillary flow structures may be spaced apart from each other at a first width configured to induce capillary flow of an underfill material along a length of the first and second elongate capillary flow structures. The first and second capillary flow structures may include pairs of elongate capillary flow structures forming passageways therebetween to induce capillary flow at an increased flow rate.