Intermetallic Solder Bump Conversion for High-Temperature Reliability
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Solution Overview
Problem
Tin-based solders used in interconnects are prone to 'tin pest' at low temperatures, leading to electrical shorting, and have limitations in high-temperature applications, such as deep oil drilling and automotive uses, due to their disintegration and whisker formation.
Innovation Solution
A method involving the deposition of nickel copper colloids surrounded by a nickel or copper shell within tin-based solder bumps, followed by a reflow process to convert the solder into an all intermetallic interconnect, which increases the melting point and prevents tin whisker formation, using low-temperature annealing steps to ensure full conversion without compromising the substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If tin-based solders are used in interconnects, then ease of manufacture is improved, but reliability deteriorates due to tin pest and tin whisker formation at low temperatures
Solution Approach 1:
The solder bump is segmented into multiple functional layers: a tin-based solder matrix containing embedded nickel-copper intermetallic colloids, surrounded by a nickel or copper shell. This segmentation allows the tin-based solder to provide ease of manufacture while the embedded intermetallic colloids prevent tin pest and whisker formation, thus maintaining reliability.
2Ease of manufacture
If tin-based solders are used in interconnects, then ease of manufacture is improved, but temperature resistance deteriorates due to disintegration at high temperatures
Solution Approach 1:
The invention creates a composite material structure where tin-based solder is combined with nickel-copper intermetallic colloids and surrounded by a nickel or copper shell. This composite structure allows the material to benefit from the ease of manufacture of tin-based solders while the intermetallic components provide high-temperature stability and prevent disintegration, thus improving temperature resistance.
3Reliability
If a second reflow process is performed to convert solder to all intermetallic interconnect, then reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The nickel-copper intermetallic colloids are pre-formed and embedded in the tin-based solder before the first reflow process. This preliminary preparation allows the second reflow process to simply activate the intermetallic conversion without requiring complex manufacturing steps, thus improving reliability while minimizing the increase in manufacturing complexity.
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 enables reliable interconnects that can withstand higher currents and temperatures, addressing the reliability concerns and tin whisker issues, expanding the application scope to include high-temperature environments like deep oil drilling and automotive systems.
Implementation Method 1
performing a second reflow process at a temperature that is lower than the first reflow process to convert the first solder bump and the second solder bump to an all intermetallic interconnect
Implementation Method 2
convert the first solder bump and the second solder bump to an all intermetallic interconnect comprising a tin nickel copper alloy
Data Source
AI summary
A method forming an interconnect structure includes depositing a first solder bump on a chip; depositing a second solder bump on a laminate, the second solder bump including a nickel copper colloid surrounded by a nickel or copper shell and suspended in a tin-based solder; aligning the chip with the laminate; performing a first reflow process to join the chip to the laminate; depositing an underfill material around the first solder bump and the second solder bump; and performing a second reflow process at a temperature that is lower than the first reflow process to convert the first solder bump and the second solder bump to an all intermetallic interconnect; wherein depositing the underfill material is performed before or after performing the second reflow process.