Flip Chip Glass Stand-offs Reduce Mechanical Stress
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Solution Overview
Problem
Existing flip chip bumping processes are costly, complex, and environmentally harmful, with high risk of wafer damage and performance issues due to extensive processing steps and the use of hazardous chemicals.
Innovation Solution
The use of glass bumps formed through photo glass processing, which provides a non-conductive stand-off feature, reduces mechanical stress and eliminates the need for expensive back-end processing steps, using a process that involves spin coating, patterning, and firing of photo glass to create glass bumps with a thermal expansion coefficient matching the substrate, allowing for accurate placement and sizing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional solder bumping or plated bumping processes are used, then conductive connections are achieved, but the manufacturing cost increases and environmental harm occurs due to extensive processing steps and hazardous chemicals
Solution Approach 1:
The patent extracts and eliminates the harmful chemical processing steps from the bumping process. Instead of using solder bumping with flux and plating with hazardous chemicals, the invention uses a pure mechanical/physical process where pre-formed bumps are attached directly to the substrate through ultrasonic welding, completely removing the need for environmentally harmful chemicals while maintaining reliable conductive connections
Solution Approach 2:
The patent replaces the chemical-based bumping process with a mechanical/physical process. Pre-formed bumps are attached using ultrasonic welding, which uses mechanical vibration and pressure instead of chemical reactions. This substitution eliminates the need for hazardous chemicals like flux and plating solutions while achieving reliable metallurgical bonds
2Manufacturing precision
If extensive processing steps are used in traditional bumping, then conductive bumps are formed, but the manufacturing complexity increases and wafer damage risk increases
Solution Approach 1:
The patent applies preliminary action by pre-forming the bumps before the actual attachment process. Bumps are created in advance with precise dimensions and metallurgical structures, then simply attached to the substrate. This eliminates the need for complex in-situ bump formation processes and reduces the number of processing steps while maintaining high precision
Solution Approach 2:
The patent merges the bump formation and attachment processes into a single integrated step. Instead of separately forming bumps and then attaching them, the pre-formed bumps are directly attached in one ultrasonic welding step, reducing process complexity and minimizing wafer handling operations that could cause damage
3Reliability
If traditional conductive bump materials are used, then electrical conductivity is achieved, but the cost increases due to expensive materials like gold and solder
Solution Approach 1:
The patent changes the material parameter of the bumps from expensive traditional materials (gold, solder) to cost-effective alternatives like aluminum or copper. These materials provide sufficient electrical conductivity for the application while dramatically reducing material costs. The ultrasonic welding process is also adapted to work with these alternative materials
4Ease of manufacture
If wafer handling steps are increased in traditional processes, then bumping is completed, but wafer breakage and damage increase impacting yield
Solution Approach 1:
The patent performs preliminary bump formation before wafer dicing and handling. By pre-forming bumps on the complete wafer and then performing ultrasonic attachment, the number of times the wafer must be handled and diced is reduced, minimizing opportunities for breakage and damage
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 mechanical stress, minimizes environmental impact, and simplifies the manufacturing process, resulting in cost-effective and reliable flip chip structures with improved yield and performance by eliminating the need for expensive and hazardous materials.
Implementation Method 1
firing of photo glass to create glass bumps
Implementation Method 2
spin coating, patterning, and firing of photo glass
Data Source
AI summary
A flip chip structure includes glass stand-offs formed overlying a substrate surface. A conductive layer is formed overlying the glass stand-offs and configured for attaching to a next level of assembly. In one embodiment, photo glass processing is used to form the glass stand-offs.