Conductive Bump Fabrication via Electroplating for Fine-Pitch Pads
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Solution Overview
Problem
The existing methods for forming conductive bumps on circuit boards, such as stencil printing and electroplating, face challenges with uneven bump height, increased difficulty due to minimal area for electroplating, and high production costs, particularly when dealing with fine-pitch electrical connection pads.
Innovation Solution
A method involving the formation of an insulating protective layer and a resist layer with openings on the circuit board, followed by a conductive layer and metal layer deposition via electroplating, allowing for even height metal bumps and reducing production costs by using copper electroplating and minimizing solder material usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If stencil printing technology is used to form solder material on electrical connection pads, then the process is simple and cost-effective, but the bump height becomes uneven and the process becomes increasingly difficult for fine-pitch pads
Solution Approach 1:
The patent replaces the mechanical stencil printing process with an electroplating process. Instead of using a physical stencil and mechanical deposition, the invention uses electrical current to deposit metal layers uniformly on the electrical connection pads through electrochemical reactions, eliminating the bump height uniformity issues associated with stencil printing
Solution Approach 2:
The patent controls the electroplating parameters (current density, plating time, electrolyte composition) to precisely control the metal layer thickness and bump height. By adjusting these parameters, uniform bumps can be formed even on fine-pitch pads, resolving the precision issue while maintaining processability
2Manufacturing precision
If direct electroplating is used on minimal area electrical connection pads, then bump height uniformity can be achieved, but the electroplating difficulty increases significantly
Solution Approach 1:
The patent applies a solder resist layer with pre-formed openings before electroplating. This preliminary step defines the exact plating areas and provides a stable substrate for uniform metal deposition, simplifying the electroplating process by pre-establishing the geometric constraints and improving current distribution
Solution Approach 2:
The solder resist layer acts as an intermediary between the electrical connection pads and the electroplating process. It provides a uniform surface for electroplating, controls the deposition area through its opening pattern, and facilitates easier process control, thereby reducing the overall process complexity
3Manufacturing precision
If conventional electroplating methods are used, then metal layers can be formed, but production costs increase and the process becomes too complex for fine-pitch applications
Solution Approach 1:
The patent optimizes electroplating parameters including using low current densities (0.1-10 mA/cm²), controlled plating times, and specific electrolyte compositions to achieve uniform deposition on fine-pitch pads. These parameter adjustments enable precise control of bump dimensions while maintaining process simplicity and cost-effectiveness
Solution Approach 2:
The patent implements process monitoring and control mechanisms to track electroplating progress and adjust parameters in real-time. This feedback control ensures consistent bump formation on fine-pitch pads while preventing defects, thereby maintaining high precision without proportionally increasing process complexity
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 ensures reliable electrical connections by achieving even bump heights, reducing production complexity and costs, and addressing issues related to minimal area electroplating, while preventing bridging and short circuits.
Implementation Method 1
forming a metal layer on the conductive layer via electroplating
Data Source
AI summary
A method for fabricating a conductive bump structure of a circuit board is disclosed. The circuit board with a plurality of electrical connection pads is provided. An insulating protective layer and a resist layer are successively applied on the circuit board, wherein openings are formed in the layers at positions corresponding to the pads to expose the pads. Then, a conductive layer is formed on surfaces of the resist layer and openings, and a metal layer is formed on the conductive layer via electroplating and filled in the openings. Subsequently, the metal layer and conductive layer formed on the resist layer are removed via thinning, so as to form metal bumps on the pads. After the resist layer is removed, the metal bumps are covered by an adhesive layer to form a conductive bump structure for electrically connecting the circuit board to the external electronic component.