Flip-Chip Package Assembly Using Shape Memory Bonding
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Solution Overview
Problem
Flip-chip integrated circuit packages are prone to mechanical stress-related failures such as cracks and delaminations due to thermal expansion coefficient mismatches between the chip and the carrier substrate, with existing solutions being either expensive or ineffective.
Innovation Solution
Incorporating a shape memory material, preferably thermally conductive nickel-titanium alloy, between the chip's rear face and the package cover, which expands upon heating to fill the gap and exert pressure, ensuring seamless electrical contact and reducing mechanical stress by acting as a spring to push the chip's protruding elements onto the substrate's contact pads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing solutions such as underfill or laser-assisted bonding are used to prevent mechanical stress failures, then reliability is improved, but manufacturing cost increases
Solution Approach 1:
The patent changes the physical state and properties of the shape memory material through temperature control. The material is heated above its transformation temperature during assembly to achieve expansion and bonding, then cooled to maintain the compressed state that provides continuous bonding pressure, eliminating the need for expensive underfill materials or laser-assisted bonding processes
Solution Approach 2:
The patent utilizes the phase transition of shape memory material between martensitic and austenitic states. During manufacturing, the material is heated above its transformation temperature to expand and fill gaps, providing bonding pressure. After cooling, the material maintains a compressed state that continues to exert bonding pressure, replacing expensive conventional bonding methods
2Strength
If conventional bonding methods are used to attach the chip to the substrate, then mechanical strength is improved, but thermal expansion stress increases
Solution Approach 1:
The patent employs shape memory material whose bonding characteristics change with temperature. At assembly temperature (above transformation point), the material is expanded and compliant, allowing stress accommodation. After cooling to operating temperature, the material contracts to provide strong bonding pressure, maintaining both strength and stress resistance
Solution Approach 2:
The patent uses shape memory material as a composite bonding agent that combines the functions of mechanical bonding and stress compensation. The material's unique property of changing dimensions with temperature allows it to provide both strong bonding strength and resistance to thermal expansion stress simultaneously
3Reliability
If the chip is physically soldered onto the substrate, then electrical connection reliability is improved, but mechanical stress and deformation increase
Solution Approach 1:
The patent replaces the mechanical soldering process with a thermal-field-based bonding mechanism. Shape memory material heated above its transformation temperature expands to make contact and establish electrical connections, then contracts upon cooling to maintain bonding pressure, eliminating the need for soldering and associated mechanical stresses
Solution Approach 2:
The patent introduces shape memory material as an intermediary between the chip and substrate for electrical connections. This material provides both electrical conductivity and mechanical compliance, allowing reliable electrical contact without the rigid mechanical constraints of traditional soldering
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 solution maintains reliable electrical connections and thermal conductivity while minimizing mechanical stress and deformation, ensuring consistent performance throughout the component's life without the need for soldering or filler materials.
Implementation Method 1
heat the package, for example to finalize the fastening of the cover on the support substrate, to a temperature which is higher than the temperature of end of transition to the austenitic state of the shape memory material, so that it expands to regain its initial shape
Implementation Method 2
The first shape memory material is advantageously thermally conductive, which also allows maintaining a thermal connection between the chip and the cover throughout the life of the component
Data Source
AI summary
An integrated circuit package includes a support substrate and a cover fastened on a first face of the support substrate. The cover and support substrate define a housing containing an electronic integrated circuit chip having a first face equipped with electrically conductive protruding elements. A first space between the cover and a second face of the electronic integrated circuit chip is filled with a first shape memory material in the austenitic state. A second space between each pair of electrically conductive protruding elements and electrically conductive contact pads of the support substrate is filled with a second shape memory material in the austenitic state.