Solder Bump Formation via Conductive Paste Sintering
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Solution Overview
Problem
Conventional solder bump formation methods using electroplating and electroless plating are costly and difficult to manage, especially for fine pitches and small bump sizes in 2.5D or 3D semiconductor packages, where stress and electro-migration issues arise due to increased current density.
Innovation Solution
A method forming solder bumps without plating by injecting conductive paste into resist openings, sintering it to create a cone-shaped metal pillar connected to electrode pads, which increases contact area with solder and prevents gas escape during bonding, using a resist layer that is later removed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If electroplating is used to form Cu pillars for fine pitch and small bump size, then manufacturing precision is improved, but production cost increases due to seed layer formation and removal
Solution Approach 1:
The invention extracts and eliminates the plating process (both electroplating and electroless plating) from the manufacturing flow. Instead of forming metal pillars through plating with seed layers, the patent uses a printed circuit board manufacturing approach where copper foil is laminated onto the substrate and patterned through etching, directly forming the conductive pillars without requiring separate seed layer formation and removal steps
Solution Approach 2:
The invention replaces expensive plating processes with cheaper PCB manufacturing techniques. The copper conductive pillars are formed using standard PCB copper foil and etching processes that are already established in the industry, eliminating the need for costly plating equipment and chemical processes
2Manufacturing precision
If electroless plating is used to form electrode pads under solder bumps, then manufacturing precision is improved, but process management becomes difficult
Solution Approach 1:
The invention extracts electroless plating from the manufacturing process and replaces it with PCB etching techniques. The electrode pads and conductive pillars are formed simultaneously through photoresist patterning and chemical etching of copper foil, eliminating the complex process management requirements of electroless plating while maintaining manufacturing precision
3Reliability
If conventional plating processes are used for solder bump formation, then reliability is improved, but device complexity increases
Solution Approach 1:
The invention merges the formation of electrode pads and conductive pillars into a single PCB manufacturing step. Both features are created simultaneously through photoresist patterning and etching of copper foil, eliminating the need for separate plating processes and reducing overall process complexity while maintaining reliability
Solution Approach 2:
The invention uses a universal PCB manufacturing approach that can form both electrode pads and conductive pillars using the same process steps (lamination, photoresist application, etching, photoresist removal). This multi-functional process replaces multiple specialized plating processes, reducing device complexity while maintaining the reliability needed for fine pitch applications
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 reduces production costs, enhances solder wetability and filling properties, and improves electro-migration resistance by forming a cone-shaped conductive layer that covers the resist layer sidewalls and electrode pads, ensuring complete solder fill and reduced voids.
Implementation Method 1
conductive paste injected in opening of the resist layer is sintered and contracted to form metal pillar (conductive layer)
Implementation Method 2
The surface of the formed metal pillars (conductive layer) has cone-shaped surface. The cone-shaped surface covers the sidewalls of the openings of the resist layer, and extends upwardly to the entrance opening. Therefore, the contact area with solder formed thereon increases.
Implementation Method 3
it is possible to prevent the gas out from the side wall of the resist layer during solder melting (bonding) and the occurrence of incomplete solder fill
Data Source
AI summary
A method of the present invention includes preparing a substrate having a surface on which a electrode pad is formed, forming a resist layer on the substrate, the resist layer having an opening on the electrode pad, filling conductive paste in the opening of the resist layer; sintering the conductive paste in the opening to form a conductive layer which covers a side wall of the resist layer and a surface of the electrode pad in the opening, a space on the conductive layer leading to the upper end of the opening being formed, filling solder in the space on the conductive layer and removing the resist layer.