Fluxless Flip-Chip Solder Bump Connection via Reducing Atmosphere
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Solution Overview
Problem
The miniaturization of solder bumps in semiconductor devices makes it difficult to completely remove flux residues, leading to voids and connection failures due to oxide film growth and trapping during the flip-chip connection process, which existing methods struggle to address effectively without increasing manufacturing costs or restricting design flexibility.
Innovation Solution
A method involving flip-chip connection without a flux agent, where solder bumps are aligned and heated to form a temporary connection, then further heated in a reducing atmosphere to remove the oxide film, using techniques such as ultrasonic energy or position adjustment to ensure direct contact and prevent oxide film entrapment, resulting in a permanent connection without voids or failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If flux is applied to remove oxide film on solder bump surface, then oxide film removal is achieved, but flux residue remains and causes voids or peeling
Solution Approach 1:
The harmful flux agent is completely removed from the process. Instead of applying flux to remove oxide films, the patent uses a reducing atmosphere (nitrogen or hydrogen) during the reflow process to prevent oxide film formation and enable direct solder bump bonding without any flux residue
Solution Approach 2:
A reducing atmosphere (nitrogen or hydrogen) is introduced into the reflow furnace to create an inert environment that prevents oxide film formation on solder bump surfaces during heating, eliminating the need for flux and preventing flux residue-related defects
2Measurement precision
If solder bump is temporarily fixed in atmosphere after oxide film removal, then position adjustment is achieved, but oxide film grows on bump surface
Solution Approach 1:
Position adjustment is performed preliminarily in a nitrogen atmosphere before the reflow process. The solder bumps are aligned and temporarily positioned while the nitrogen atmosphere prevents oxide film growth, and this position is maintained through the subsequent reflow process
Solution Approach 2:
Nitrogen atmosphere is maintained during position adjustment and temporary fixing to prevent oxide film growth on solder bump surfaces, ensuring that no oxide films are present when the bumps are bonded during reflow
3Measurement precision
If conventional flip-chip bonder position adjustment is applied, then position accuracy is achieved, but spacer made of solder is required increasing cost
Solution Approach 1:
The patent changes the atmospheric parameter (introducing nitrogen atmosphere) to enable direct solder bump bonding without requiring solder spacers. This parameter change allows conventional flip-chip bonders to achieve position accuracy while eliminating the need for additional spacer materials and reducing manufacturing costs
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 enables reliable and cost-effective flip-chip connections by preventing oxide film entrapment and voids, maintaining a spherical connection shape without constricted portions, thus enhancing the reliability and efficiency of semiconductor device manufacturing.
Implementation Method 1
melting the first and second solder bumps by performing heating to a temperature equal to or higher than a melting point of the first and second solder bumps
Implementation Method 2
heating the partially connection body after the cooling to a temperature equal to or higher than the melting point of the first and second solder bumps in a reducing atmosphere, to form a permanent connection body by melting the partially connection body while removing an oxide film
Data Source
AI summary
According to a manufacturing method of one embodiment, a first solder bump and a second solder bump are aligned and placed in contact with each other, and thereafter, the first and second solder bumps are heated to a temperature equal or higher than a melting point of the solder bumps and melted, whereby a partially connection body of the first solder bump and the second solder bump is formed. The partially connection body is cooled. The cooled partially connection body is heated to a temperature equal to or higher than the melting point of the solder bump in a reducing atmosphere, thereby to form a permanent connection body by melting the partially connection body while removing an oxide film existing on a surface of the partially connection body.