Package Substrate Warpage Control via Tin-Copper Alloy Post Terminal
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Flip chip packages face reliability issues due to warpage between substrates and chips, particularly with copper posts that are prone to oxidation and cracking, and replacing copper with metallic alloys leads to separation problems and undesired plating.
Innovation Solution
A package substrate with a copper separation barrier layer and a tin-copper alloy post terminal, where the separation barrier layer is formed to prevent plating solution leakage and the post terminal is electroplated with a specific current density to control warpage, topped with a tin-bismuth solder bump for improved ductility and lower melting point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If copper post is used for bump structure, then mechanical strength and stability are improved, but oxidation resistance and crack resistance deteriorate due to great hardness
Solution Approach 1:
The patent uses a composite structure consisting of a copper post combined with a tin-plated layer. The copper post provides mechanical strength and stability, while the tin plating layer provides oxidation resistance and ductility. This composite material approach resolves the contradiction by combining materials with complementary properties.
Solution Approach 2:
The patent applies different material properties to different parts of the bump structure. The copper post (inner core) provides mechanical strength, while the tin-plated surface (outer layer) provides oxidation resistance and crack resistance. This local differentiation of material quality allows each layer to perform its specific function optimally.
2Reliability
If metallic alloy is used to replace copper post, then oxidation resistance is improved, but separation between metal seed layer and dry film occurs leading to undesired plating
Solution Approach 1:
The patent uses a specific plating seed layer as an intermediary between the metallic alloy post and the dry film. This seed layer, composed of copper or copper alloy, serves as a mediator that ensures good adhesion between the alloy post and the subsequent insulating layer, preventing separation and undesired plating while maintaining the oxidation resistance benefits of the alloy.
Solution Approach 2:
The patent optimizes the composition parameters of the plating seed layer, specifying it should be copper or copper alloy with controlled copper content. By adjusting these compositional parameters, the patent achieves both good adhesion (preventing separation) and compatibility with the dry film process, thereby maintaining manufacturing precision while using metallic alloys.
3Productivity
If bump pitch is decreased for high-speed large-capacity data processing, then data processing capacity is improved, but bump reliability deteriorates
Solution Approach 1:
The patent changes the material composition parameters of the bump structure, using metallic alloys with specific copper content (0.2-4 wt%) combined with tin plating. This compositional parameter change allows the bumps to maintain reliability even at decreased pitch by providing better oxidation resistance and controlled warpage, enabling high-density packaging for high-speed data processing.
Solution Approach 2:
The patent employs a composite bump structure with metallic alloy post and tin plating that provides enhanced mechanical and chemical properties. This composite design allows smaller bump sizes with decreased pitch while maintaining or improving reliability through the synergistic properties of the combined materials, supporting high-speed large-capacity data processing requirements.
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 solution effectively controls warpage and prevents undesired plating, maintaining the reliability of the solder bumps and preventing post terminal melting during reflow, thus enhancing the overall reliability of the flip chip package.
Implementation Method 1
the separation barrier layer prevents a plating solution for the post terminal from leaking through an interface between the insulating layer and a dry film pattern
Implementation Method 2
the separation barrier layer and the post terminal are formed by electroplating
Data Source
AI summary
There is provided a package substrate capable of controlling the degree of warpage thereof by improving the composition and formation of a post terminal and a method of fabricating the same. The package substrate includes a substrate having at least one conductive pad; an insulating layer provided on the substrate and having an opening to expose the conductive pad; a separation barrier layer provided on the conductive pad inside the opening and formed to be higher than the upper surface of the insulating layer along the side walls thereof; a post terminal provided on the separation barrier layer; and a solder bump provided on the post terminal.