Copper Pillar Bump Structure for Stress-Resistant Flip Chip Packaging
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Solution Overview
Problem
Copper pillar bump technology induces larger stress in packaging due to thermal expansion differences, leading to delamination and crack issues in adjacent vulnerable layer structures during reflow processes and thermal cycling tests, affecting the reliability of flip chip packages.
Innovation Solution
Replace parts of the copper pillar with a metal bump to absorb excess stress, using a copper pillar structure with a lower part and an upper part, where the metal bump directly contacts the second upper surface of the lower part, increasing the volume ratio of the metal bump to prevent delamination and cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper pillar bump technology is used to improve signal transduction and thermal conductivity, then electrical and thermal performance is improved, but larger stress is induced due to thermal expansion differences causing delamination and crack issues
Solution Approach 1:
The copper pillar is divided into two distinct parts: a lower part with larger diameter that remains copper for thermal/electrical conduction, and an upper part with smaller diameter that is replaced by metal bump for stress absorption. This segmentation allows each part to fulfill different functional requirements simultaneously.
Solution Approach 2:
Different materials are used at different locations of the pillar structure. The lower part uses copper material optimized for thermal and electrical conductivity, while the upper part uses metal bump material optimized for stress absorption and ductility, creating local quality optimization throughout the structure.
2Productivity
If fine pitch between copper pillar bumps is scaled down to increase capacity, then integration density is improved, but stress concentration increases leading to higher risk of delamination and cracking
Solution Approach 1:
The pillar structure is segmented into lower and upper parts with different materials and dimensions, allowing the upper metal bump portion to absorb stress while maintaining fine pitch spacing between adjacent bumps for high integration density.
Solution Approach 2:
The pillar structure employs composite construction combining copper material in the lower part with metal bump material in the upper part, creating a composite structure that leverages the advantageous properties of both materials to simultaneously achieve fine pitch compatibility and stress resistance.
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 design effectively absorbs excess stress during reflow soldering, preventing delamination and cracking of adjacent vulnerable layers, thereby enhancing the reliability of the copper pillar bump structure.
Implementation Method 1
absorb excess stress through the metal bump and prevent the delamination or crack of adjacent vulnerable layer structures
Implementation Method 2
performing a first electroplating process using the first photoresist as a mask to form a lower copper pillar connecting the bonding pad
Data Source
AI summary
A method of manufacturing a copper pillar bump structure, including forming a 1st photoresist on a passivation layer, wherein 1st photoresist has a 1st copper pattern exposing a bonding pad, performing a 1st electroplating process using 1st photoresist as mask to form a lower copper pillar connecting the bonding pad, forming a 2nd photoresist on the passivation layer, wherein 2nd photoresist has a 2nd copper pillar pattern exposing parts of the lower copper pillar, performing a 2nd electroplating process using 2nd photoresist as mask to form an upper copper pillar connecting with the lower copper pillar, forming a 3rd photoresist on the passivation layer, wherein 3rd photoresist has a metal pattern exposing the upper copper pillar and parts of the lower copper pillar, and performing a 3rd electroplating process using 3rd photoresist as mask to form a metal bump on the upper copper pillar and the lower copper pillar.