Flip Chip Solder Bump Support Pillars for Mechanical Stability
Solution Overview
Problem
Conventional flip chip solder bump structures face reliability issues due to mechanical and metallurgical weaknesses, particularly in the under-bump metallization region, and are not suitable for lead-free solder materials, leading to potential cracking, delamination, and electrical failures as device sizes shrink.
Innovation Solution
The development of a semiconductor device with support pillars within the solder bump structure, where a conductive material is deposited between sacrificial posts and a passivation layer is used to form these pillars, enhancing mechanical stability and allowing for lead-free solder use, with an under-bump metallization layer between the pillars and the passivation layer for improved bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional flip chip solder bump structures are used, then the manufacturing process is simple, but the reliability is poor due to mechanical and metallurgical weaknesses in the under-bump metallization region
Solution Approach 1:
The solder bump structure is segmented into multiple functional layers: support pillars (first material), under-bump metallization (second material), and solder bump (third material). This segmentation allows each layer to be optimized for its specific function, with the support pillars providing mechanical strength and the UBM providing metallurgical bonding, thereby resolving the reliability issue while maintaining manageable complexity through modular design
Solution Approach 2:
The invention uses composite material structures where the support pillars are made of a first material, the under-bump metallization is made of a second material, and the solder bump is made of a third material. This composite approach allows each material to be selected for its optimal properties (mechanical strength, bonding capability, solder compatibility), directly addressing the reliability problems of conventional single-material structures
2Strength
If the under-bump metallization thickness is increased to improve mechanical strength, then the mechanical stability improves, but the total thickness exceeds the available space below the solder bump
Solution Approach 1:
The mechanical support function is segmented from the metallurgical bonding function. Support pillars made of a first material provide the necessary mechanical strength and stability, while the under-bump metallization made of a second material provides the bonding interface. This segmentation allows the support structure to be optimized for strength without requiring excessive total thickness, as the pillars provide structural integrity with minimal material volume
Solution Approach 2:
Different regions of the structure have different material properties optimized for their specific functions. The support pillars have high mechanical strength properties, the UBM has optimal bonding properties, and the solder bump has optimal solderability. This local optimization allows each component to achieve its required performance with minimal thickness, resolving the contradiction between mechanical stability and total thickness
3Adaptability or versatility
If lead-free solder materials are used, then the environmental compliance improves, but the mechanical and metallurgical reliability deteriorates due to cracking and delamination
Solution Approach 1:
The composite material structure with support pillars (first material), UBM (second material), and lead-free solder bump (third material) provides both the environmental compliance of lead-free materials and the metallurgical reliability needed to prevent cracking and delamination. The specialized UBM layer is specifically designed to bond reliably with lead-free solder materials
Solution Approach 2:
The support pillars and under-bump metallization layer act as a cushioning structure that prevents stress concentration and delamination at the solder- substrate interface. This pre-engineered support structure compensates for the inherently lower reliability of lead-free solder materials, preventing cracking and delamination before they can occur during thermal cycling or mechanical stress
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 configuration provides enhanced mechanical stability and reliability by increasing the surface area and anchoring of the solder bumps, reducing oxidation, and allowing for the use of lead-free materials, while simplifying the manufacturing process and improving yield.
Implementation Method 1
depositing a conductive material between the spaced apart sacrificial posts and within the solder bump support opening
Implementation Method 2
removing the lithographic resist layer, thereby leaving the conductive material within the solder bump support opening to form support pillars
Data Source
AI summary
The invention provides, in one aspect, a semiconductor device that comprises an interconnect layer located over a semiconductor substrate. A passivation layer is located over the interconnect layer and having a solder bump support opening formed therein. Support pillars that comprise a conductive material are located within the solder bump support opening.