Flip Chip Underfill Fillet Control via Non-Wettable Zones
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Solution Overview
Problem
Microelectronic assemblies with flip chip underfill experience corner cracking and stress-induced failures due to thermal cycling, which compromises the reliability of solder bump interconnections and underfill material.
Innovation Solution
Creating non-wettable zones on the chip and substrate to limit the underfill fillet within the chip shadow line, reducing the path for crack propagation and eliminating common crack initiation points by modifying the fillet location and removing traditional fillets that extend beyond the chip shadow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the underfill fillet extends beyond the chip shadow line to strengthen the assembly, then the bonding strength is improved, but crack propagation paths are created that reduce reliability
Solution Approach 1:
The patent extracts and removes the harmful portion of the fillet that extends beyond the chip shadow line. By eliminating this external fillet portion, the crack propagation path is removed while maintaining the essential bonding function within the shadow line area.
Solution Approach 2:
The patent applies different fillet configurations to different locations: within the chip shadow line, the fillet provides bonding strength, while beyond the shadow line, the fillet is removed to prevent cracking. This location-specific approach optimizes both strength and reliability.
2Duration of action of stationary object
If thermal cycling is experienced during operation to test assembly durability, then the assembly undergoes stress testing, but thermal stresses cause underfill cracking and solder joint fatigue
Solution Approach 1:
The patent applies preliminary anti-action by removing the external fillet portion before thermal cycling occurs. This pre-emptive modification eliminates the stress concentration points that would otherwise be created during thermal cycling, preventing crack initiation and propagation.
Solution Approach 2:
The patent converts the harmful effect of thermal stress into a benefit by redesigning the fillet geometry. The modified fillet configuration within the shadow line actually improves thermal stress distribution and reduces cracking during thermal cycling operations.
3Object-affected harmful factors
If a traditional fillet is formed beyond the chip shadow line to protect solder bumps, then environmental protection is improved, but crack initiation points are created that reduce interconnection reliability
Solution Approach 1:
The patent extracts and removes the external fillet portion beyond the chip shadow line that serves as a crack initiation point. This removal eliminates the harmful effect while the underfill material still provides environmental protection through capillary action into the gap.
Solution Approach 2:
The patent uses the chip shadow line as an intermediary boundary to define where the fillet should end. This boundary serves as a mediator between the need for environmental protection and the need to prevent crack initiation, with the underfill material providing protection without the harmful external fillet.
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 approach enhances the thermal cycling life of microelectronic assemblies by reducing underfill cracking and stress concentrations, thereby improving the reliability of electrical interconnections and extending the assembly's useful life.
Implementation Method 1
A curable polymeric underfill material is dispensed onto the supporting substrate adjacent to the die 10 and is drawn into the gap by capillary action.
Implementation Method 2
The polymeric material is then cured, typically by heating, to form the underfill.
Data Source
AI summary
A method of assembling a microelectronic flip-chip arrangement includes attaching a chip having a defined length to a supporting substrate, wherein the chip forms a chip shadow line of the defined length on the supporting substrate, creating a first non-wettable zone on an outer portion of the bottom surface of the chip, creating a second non-wettable zone on a portion of the supporting substrate outside the chip shadow line, underfilling the chip and forming a fillet, wherein the fillet does not extend beyond the chip shadow line, and hardening the underfill including the fillet.