Flip Chip Warpage Suppression via Localized Heating and Pressure
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Solution Overview
Problem
The mismatch in coefficients of thermal expansion between semiconductor chips and organic substrates during flip chip assembly leads to mechanical stress, warpage, and failure in solder bonding, resulting in non-wetting and bridging issues, which decrease assembly yield.
Innovation Solution
A flip chip assembly apparatus with a warpage-suppressor assembly that includes a side heater and a deformable material pad, which applies additional heat and pressure to the peripheral solder balls and substrate to prevent warpage during the reflow process, ensuring reliable solder bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional reflow process is used for flip chip assembly on organic substrate, then solder balls can be reflowed, but substrate warpage occurs causing non-wetting and bridging between solder bumps
Solution Approach 1:
The patent applies different thermal conditions to different regions of the substrate. Side heaters are positioned at the periphery of the substrate to provide localized heating to the edge portions, while the center region is heated by the bonder head. This creates a temperature gradient that compensates for the differential thermal expansion between the organic substrate and semiconductor chip, preventing warpage and ensuring uniform solder bonding across the substrate surface.
2Adaptability or versatility
If organic substrate is used for packaging, then cost and flexibility are improved, but CTE mismatch with semiconductor chip causes mechanical stress and warpage
Solution Approach 1:
The patent modifies the thermal parameters during the reflow process by introducing side heaters that heat the periphery of the organic substrate to a temperature higher than the center region. This parameter change compensates for the higher thermal expansion of the organic substrate at the edges, reducing the CTE mismatch stress and preventing warpage while maintaining the advantages of using organic substrates.
3Manufacturing precision
If heat is applied uniformly during reflow, then solder balls reflow evenly, but peripheral solder balls experience insufficient heat due to substrate warpage
Solution Approach 1:
The patent implements localized heating at the periphery of the substrate using side heaters positioned around the edges. This ensures that peripheral solder balls receive sufficient heat for proper reflow, compensating for the heat loss that occurs due to substrate warpage and the greater distance from the center heating source. The side heaters create a temperature distribution that ensures uniform solder bonding across the entire substrate surface.
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
The solution effectively minimizes substrate warpage and ensures reliable solder bonding by providing additional heat and pressure, reducing mechanical stress and improving assembly yield by maintaining contact between solder balls and bonding pads.
Implementation Method 1
Each side heater provides additional heat to peripheral solder balls during bonding of two substrates, thereby facilitating the reflow of the peripheral solder balls
Implementation Method 2
Each deformable material pad contacts, and presses down on, a surface of one of the two substrates under bonding. The deformable material pad(s) can prevent or minimize warpage of the contacted substrate
Implementation Method 3
facilitating the reflow of the peripheral solder balls
Implementation Method 4
organic substrates expand and contract more than silicon chips. Such a mismatch between CTE's can create thermally-induced stress and strain in a bonded flip-chip structure
Data Source
AI summary
A flip chip assembly apparatus includes at least one warpage-suppressor assembly. Each warpage-suppressor assembly can include a side heater, a deformable material pad, and an actuator assembly for moving the side heater and the deformable material pad. Each side heater provides additional heat to peripheral solder balls during bonding of two substrates, thereby facilitating the reflow of the peripheral solder balls. Each deformable material pad contacts, and presses down on, a surface of one of the two substrates under bonding. The deformable material pad(s) can prevent or minimize warpage of the contacted substrate.