Chip-to-Substrate Solder Assembly Using Pre-Cooldown Underfill
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Solution Overview
Problem
The miniaturization of IC technology faces challenges in interconnecting chips with high-density bump interconnection and organic laminate substrates due to connector pitch limitations and thermal strain caused by coefficient of thermal expansion mismatches, leading to misalignment and misconnections at sub-55 μm pitches.
Innovation Solution
The method involves bonding a semiconductor chip to an organic laminate substrate using solder, dispensing underfill without cooldown from the bonding temperature, and curing it within a specific temperature range, while using solder caps on both chip pillars and substrate pads to accommodate warpage and reduce thermal strain, and applying volatile tacky adhesive for additional attachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If connector pitch is reduced to increase data transfer density, then data transfer efficiency is improved, but thermal strain and misalignment risk increase
Solution Approach 1:
The underfill is dispensed and cured before the cooldown process to pre-establish mechanical support and strain distribution pathways. This preliminary action prevents misalignment from occurring during the subsequent thermal contraction, as the underfill already provides a cushioning matrix that accommodates dimensional changes.
Solution Approach 2:
The underfill material serves as a cushioning layer between the chip and substrate that absorbs and distributes thermal strain before it can cause misalignment or damage to the fine-pitch connectors. By placing this protective layer in advance, the system gains resilience against the harmful effects of thermal expansion mismatches.
2Area of moving object
If chip connector pitch is tightened to increase density, then integration density is improved, but thermal strain causes misalignment
Solution Approach 1:
The invention changes the temporal parameter of the underfill curing process by performing it at elevated temperature before cooldown. This parameter change ensures that the underfill achieves optimal mechanical properties while the chip and substrate are still dimensionally stable, thereby locking in alignment precision before thermal contraction occurs.
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 reliability of solder connections at sub-55 μm pitches by reducing thermal strain and protecting chip connectors from shear stress, enabling more efficient data transfer and improved chip-to-substrate bonding performance.
Implementation Method 1
bonding a semiconductor chip to an organic laminate substrate using solder
Implementation Method 2
Thermal strain, caused by differences in coefficient of thermal expansion (CTE) between semiconductor chips and organic laminate substrates
Implementation Method 3
applying volatile tacky adhesive for additional attachment
Data Source
AI summary
An exemplary method includes at a bonding temperature, bonding a semiconductor chip to an organic laminate substrate using solder; without cooldown from the bonding temperature to room temperature, at an underfill dispense temperature, dispensing underfill between the semiconductor chip and the organic laminate substrate; and curing the underfill within a range of temperatures above the underfill dispense temperature. Another exemplary method includes depositing a first solder on pads of an organic laminate substrate; contacting a second solder on pillars of a semiconductor chip to the first solder on the pads of the organic laminate substrate; and solder bonding the semiconductor chip to the organic laminate substrate.