Flip-Chip Copper Pillar Packaging Process
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Solution Overview
Problem
Conventional flip-chip packaging processes using solder bumps face issues with insufficient strength and capacitance density, difficulty in controlling the etching of the under bump metallurgy (UBM) layer, and require complex reflow steps, which hinder the development of high-speed charging and discharging elements.
Innovation Solution
The process replaces solder bumps with copper pillars, where a copper pillar is formed on a wafer with a bond pad and passivation layer, and then embedded in solder on a substrate, covering all external surfaces, allowing for improved etching control and eliminating the need for reflow steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solder bumps are used in conventional flip-chip packaging, then the connection is formed, but the strength and capacitance density are insufficient for high-speed charging and discharging elements
Solution Approach 1:
The patent changes the material parameter from solder to copper, forming copper pillars instead of solder bumps. This material substitution provides higher strength and capacitance density while maintaining electrical connection functionality, directly addressing the insufficient strength and capacitance density of conventional solder bumps for high-speed applications
Solution Approach 2:
The patent creates a composite structure by embedding copper pillars in solder material. The copper pillar provides high strength and capacitance density, while the surrounding solder material ensures reliable bonding and electrical connection, combining the advantages of both materials to achieve both high performance and reliability
2Manufacturing precision
If conventional etching process is used for UBM layer, then the UBM layer is removed, but the etching selectivity between solder bumps and UBM layer is poor making the step difficult to control
Solution Approach 1:
The patent changes the material parameter from solder to copper for the pillar structure. This creates better etching selectivity between copper and the UBM layer compared to solder and UBM, making the etching process easier to control and achieve higher manufacturing precision in removing the UBM layer
3Device complexity
If reflow steps are used in conventional process, then the solder bumps are melted and formed, but the entire process becomes quite complicated
Solution Approach 1:
The patent extracts and eliminates the reflow step from the conventional process by using copper pillars instead of solder bumps. Since copper pillars are formed through electroplating or printing without requiring melting, the complex reflow process is removed, simplifying the entire fabrication process while maintaining precise bump structure formation
Solution Approach 2:
The patent replaces the thermal-mechanical process (reflow melting) with a electrochemical or printing process (electroplating/printing). This substitution eliminates the need for high-temperature reflow steps, reducing process complexity while achieving precise copper pillar formation through controlled deposition
4Object-affected harmful factors
If copper pillar is exposed to ambience, then the external surfaces are accessible, but oxidation occurs on the copper pillar surfaces
Solution Approach 1:
The patent introduces solder material as an intermediary substance that surrounds and covers the copper pillar. This solder material acts as a protective barrier between the copper surface and the ambient environment, preventing oxidation while allowing the copper pillar to maintain its structural strength and electrical properties
Solution Approach 2:
The solder material creates an inert protective environment around the copper pillar, isolating it from oxygen in the ambient atmosphere. This effectively creates a localized inert environment that prevents oxidation of the copper surface while maintaining the structural integrity and strength of the copper pillar
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 provides copper pillars with high strength and capacitance density, simplifies the processing steps by eliminating reflow, and prevents oxidation of the copper pillar surfaces.
Implementation Method 1
a copper material is filled into the opening
Implementation Method 2
the solder covers substantially all of the external surfaces of the copper pillar
Data Source
AI summary
A flip-chip packaging process is disclosed. The present invention is featured in forming a copper pillar on a wafer, forming a solder on a substrate; and enabling the solder to substantially cover the entire externally-exposed surface of the copper pillar, thereby connecting the copper pillar to the substrate. The copper pillar of the present invention can be such as a prism or a cylinder.