High Aspect Ratio Solder Bump Fabrication via Stud Base and Injection
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Solution Overview
Problem
Conventional bumping technologies face challenges in forming high aspect ratio bumps with sufficient conductive material, particularly due to residual gas in resist masks leading to low solder filling yield and insufficient solder material, which affects the reliability of electrical connections.
Innovation Solution
A method involving forming a bump base with a tip extending outward from each pad, followed by patterning holes in a resist layer aligned with the pads, and filling these holes with molten conductive material, such as solder, to create high aspect ratio solder capped bumps, optimizing solder composition for improved mechanical characteristics and electro-migration resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional IMS technology is used to form solder bumps, then solder filling can be achieved, but residual gas in high aspect holes prevents solder material from reaching the pillar and wetting on the top face, resulting in low solder filling yield
Solution Approach 1:
The patent applies preliminary action by forming a protruding structure (stud bump or metal pillar) that extends beyond the resist mask surface before solder injection. This pre-formed structure creates a pathway for solder material to reach the bottom of high aspect ratio holes, overcoming the barrier of residual gas that would otherwise prevent solder from contacting the pillar top surface.
2Length of stationary object
If high aspect ratio bumps are required for thick waveguide layers, then electrical connection through thick substrates is enabled, but sufficient conductive material cannot be efficiently fabricated with conventional bumping techniques
Solution Approach 1:
The patent implements the nested doll principle by creating a multi-layer conductive structure where a stud bump or metal pillar is embedded within injected solder material. This nested configuration (metal core surrounded by solder) efficiently packs conductive material to achieve high aspect ratios while ensuring sufficient conductive cross-section for reliable electrical connection through thick waveguide layers.
3Reliability
If electroplating processes are used to form metal pillars, then conductive bases can be created, but expensive electroplating equipment and processes are required
Solution Approach 1:
The patent applies this principle by replacing expensive electroplating processes with cheaper alternative methods such as wire bonding to form stud bumps or using simple metal deposition techniques. These cost-effective methods create sufficient conductive bases that can be integrated with injected solder material, achieving reliable electrical connection without requiring expensive electroplating equipment and processes.
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 enhances the filling yield of solder material, ensures a sufficient amount of conductive material in the bumps, and reduces production costs by eliminating the need for expensive electroplating processes, resulting in higher reliability and improved mechanical characteristics of electrical connections.
Implementation Method 1
The IMS is technology that forms solder bumps on a substrate such as a wafer by injecting molten solder into holes in a resist mask
Implementation Method 2
The tip of the bump base would touch the molten solder in the hole at the beginning of the filling, making it easier for the molten solder to wet the top of the tip and enter the hole
Implementation Method 3
The conductive material is solder material and injected into each hole in molten state
Data Source
AI summary
A technique for fabricating bumps on a substrate is disclosed. A substrate that includes a set of pads formed on a surface thereof is prepared. A bump base is formed on each pad of the substrate. Each bump base has a tip extending outwardly from the corresponding pad. A resist layer is patterned on the substrate to have a set of holes through the resist layer. Each hole is aligned with the corresponding pad and having space configured to surround the tip of the bump base formed on the corresponding pad. The set of the holes in the resist layer is filled with conductive material to form a set of bumps on the substrate. The resist layer is stripped from the substrate with leaving the set of the bumps.