Multi-Layer Conductive Bump for Flip-Chip Packaging
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional flip-chip packaging processes face challenges in controlling the volume and height of solder bumps, leading to potential short circuits and poor coplanarity, especially when using low-k materials which are prone to cracking under high compression forces and temperatures during thermal compression bonding (TCB).
Innovation Solution
A conductive bump structure comprising three metal layers with different melting points is used, where the third metal layer and solder material are bonded at a low temperature and low compression force, and the second metal layer is melted to form an alloy with the third metal layer and solder material at a higher temperature, forming a conductor that avoids substrate cracking and enhances reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional solder bump formation is used, then electrical connection is achieved, but the volume and height of solder bumps cannot be controlled, leading to short circuits and poor coplanarity
Solution Approach 1:
The conductive bump is segmented into multiple metal layers (first metal layer, second metal layer, third metal layer) with different melting points. This segmentation allows independent control of formation processes for each layer, enabling precise control of overall bump volume and height while maintaining reliability.
Solution Approach 2:
The invention utilizes parameter changes by employing metal layers with different melting points. The third metal layer (lower melting point) is formed first at lower temperature, followed by the second metal layer (higher melting point) at higher temperature. This parameter-based sequential formation enables precise control of bump geometry.
2Strength
If thermal compression bonding (TCB) process is used with low-k materials, then bonding is achieved, but the substrate is prone to cracking due to ultra high compression force and temperature
Solution Approach 1:
The invention changes the temperature parameter by using a multi-layer structure with different melting points. The lower melting point third metal layer allows bonding at reduced temperature compared to conventional TCB, thereby preventing substrate cracking while still achieving sufficient bonding strength.
Solution Approach 2:
The conductive bump uses a composite multi-layer metal structure where each layer has different properties (different melting points). This composite structure enables the bonding process to occur at lower temperatures than conventional single-material bumps, protecting the low-k substrate from thermal damage.
3Manufacturing precision
If fine-pitch requirements are met with controlled solder bumps, then signal transmission quality improves, but the process complexity increases due to need for precise volume and height control
Solution Approach 1:
The complex task of controlling bump geometry is segmented into two simpler sub-tasks: forming the third metal layer at lower temperature, then forming the second metal layer at higher temperature. This segmentation simplifies the overall process while achieving the required fine-pitch precision and coplanarity.
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 allows for a low-temperature TCB process that prevents substrate cracking and improves the reliability of conductors by forming an alloy with a high melting point, meeting fine-pitch requirements and ensuring reliable signal transmission in miniaturized electronic devices.
Implementation Method 1
heating the substrate and the carrier to a first temperature range, allowing the third metal layer to be melted and thereby bonded with the carrier
Implementation Method 2
heating the substrate and the carrier to a second temperature range, allowing the second metal layer to be melted to form an alloy portion with the third metal layer
Data Source
AI summary
A conductive bump structure used to be formed on a substrate having a plurality of bonding pads. The conductive bump structure includes a first metal layer formed on the bonding pads, a second metal layer formed on the first metal layer, and a third metal layer formed on the second metal layer. The second metal layer has a second melting point higher than a third melting point of the third metal layer. Therefore, a thermal compression bonding process is allowed to be performed to the third metal layer first so as to bond the substrate to another substrate, and then a reflow process can be performed to melt the second metal layer and the third metal layer into each other so as to form an alloy portion, thus avoiding cracking of the substrate.