Circuit Board Copper Oxide Layer for Flip Chip Solder Bump Placement
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Solution Overview
Problem
The challenge in flip chip mounting is to decrease the pitch between electrodes and form minute solder bumps on a semiconductor element, as existing techniques face difficulties in forming complex conductor patterns and accurately placing small solder balls.
Innovation Solution
A circuit board with a copper layer and a copper oxide layer, where the copper oxide layer is partially removed to expose the copper layer, allowing for the formation of solder bumps using cream solder that adheres to the copper but not the copper oxide, enabling easy adjustment of bump size and pitch without complicating the electrode shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a solder ball mounting method is used to form minute solder bumps, then the pitch between electrodes can be decreased, but it becomes difficult to accurately place the small solder balls on the electrodes
Solution Approach 1:
The invention changes the state of the electrode surface by forming a copper oxide layer with specific properties (thickness of 5-50 nm). This parameter change enables selective adhesion where solder adheres to copper oxide regions while repelling from copper regions, allowing precise placement of minute solder bumps even at reduced pitches without requiring complex positioning systems
Solution Approach 2:
The copper oxide layer acts as an intermediary between the copper electrode and the solder. By controlling the adhesion properties of the copper oxide layer, the invention mediates the interaction between solder and electrode, enabling accurate placement of minute solder balls through chemical affinity rather than mechanical positioning
2Productivity
If the pitch between bumps on semiconductor element is decreased, then the density of semiconductor elements can be increased, but it becomes necessary to form minute solder bumps which are difficult to place accurately
Solution Approach 1:
The invention changes the surface parameters of the electrode by forming a copper oxide layer with controlled thickness (5-50 nm). This enables the formation of minute solder bumps with high precision at increased densities by utilizing the selective adhesion properties of copper oxide, allowing higher productivity without sacrificing manufacturing precision
Solution Approach 2:
The invention applies local quality by creating regions with different adhesion properties on the electrode surface. The copper oxide layer is formed selectively in specific regions, creating local areas where solder will adhere, while other regions remain non-adhesive. This allows precise control of solder bump formation at high densities
3Manufacturing precision
If a complex conductor pattern structure is used, then the solder bump can be formed at the correct position, but the pitch between electrodes cannot be easily decreased
Solution Approach 1:
The invention changes the chemical properties of the electrode surface by forming a copper oxide layer, replacing the need for complex geometric patterns. This parameter change from physical structure to chemical property simplifies the conductor pattern while maintaining precise solder bump positioning capability
Solution Approach 2:
The invention replaces the mechanical approach of using complex conductor pattern geometries with a chemical approach using copper oxide layer adhesion properties. This substitution simplifies the physical structure while achieving the same positioning function through chemical affinity
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 method allows for the easy formation of minute solder bumps and reduction of electrode pitch, improving adhesion with underfill and enhancing the reliability of the flip-chip mounting process by controlling the active force of the flux to prevent removal of the copper oxide layer.
Implementation Method 1
solder is likely to be adhered to copper but is not likely to be adhered to copper oxide
Implementation Method 2
when the cream solder is heated, the solder bump is formed on the copper layer
Data Source
AI summary
A circuit board includes: an electrode portion which has a copper layer, a copper oxide layer formed thereon, and a removal portion formed by partially removing the copper oxide layer so as to partially expose the copper layer from the copper oxide layer; and a solder bump for flip chip mounting formed on the copper layer exposed by the removal portion.