Multi-Layer Bump Formation via Laser Masking
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Solution Overview
Problem
Conventional methods for forming conductive bumps on semiconductor chips or printed circuit boards are costly, generate chemical waste, and face limitations in achieving high standoff and low pitch due to the use of photoresist layers and wet chemical processes.
Innovation Solution
A method using metal powders and an adhesive or flux to form multi-layer bumps, where a masking plate with apertures is used to direct an irradiation beam to clean and form bumps, allowing for high standoff and fine pitch without the need for wet chemicals or extensive tooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a thicker photoresist layer is used to obtain higher bump standoff, then the standoff height is improved, but the maximum possible thickness is limited by low or fine pitch requirements
Solution Approach 1:
The patent transitions from a single-layer photoresist approach to a multi-layer bump structure. Instead of increasing photoresist thickness in one dimension, the invention builds bumps vertically in multiple layers, where each layer is formed and then planarized. This allows achieving high standoff heights without increasing the lateral dimensions that would conflict with fine pitch requirements.
Solution Approach 2:
The bump formation process is segmented into multiple discrete steps, with each step forming a portion of the final bump height. The photoresist layer is applied, patterned, and cured in repeated cycles, with each cycle adding a layer to the bump structure. This segmentation allows precise control over both the final height and the pitch, as each layer can be independently optimized.
2Ease of manufacture
If conventional photoresist and wet chemical methods are used to form bumps, then the bump formation process is established, but hazardous chemicals are required and chemical waste is generated
Solution Approach 1:
The patent replaces wet chemical etching and development processes with a thermal curing approach. Instead of using chemical solutions to pattern and remove photoresist, the invention uses controlled heating to cure the photoresist layers and remove unwanted material. This substitution eliminates the need for hazardous chemical waste treatment while maintaining the bump formation capability.
Solution Approach 2:
The patent changes the processing parameters from chemical-based to thermal-based. By controlling temperature profiles during curing and processing, the invention achieves the same patterning and material removal functions that previously required chemical solutions. This parameter change eliminates chemical waste generation while preserving manufacturing effectiveness.
3Adaptability or versatility
If a new photoresist layer is required for processing each wafer, then the photoresist mask can be customized, but processing costs increase
Solution Approach 1:
The patent creates a universal photoresist mask system that can be reused across multiple wafers. Instead of requiring a new photoresist layer for each wafer, the invention develops a mask structure that maintains its functionality through multiple processing cycles. The mask can be refreshed or repositioned, allowing the same mask to serve multiple wafers, thereby reducing material costs while preserving the ability to customize patterns.
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 reduces processing costs, eliminates the use of hazardous chemicals, and achieves high standoff and fine pitch, improving bump joint reliability by minimizing thermal-mechanical stress from coefficient of thermal expansion mismatch.
Implementation Method 1
A localized irradiation beam is provided over the masking plate and directed at the bump sites. The beam cleans and removes contaminants from the pads.
Implementation Method 2
The selected portions of the metal powder are thus melted or reflowed to form a number of first bumps on the bond pads
Implementation Method 3
The beam melts or reflows the solder paste to form a bump
Implementation Method 4
A method using metal powders and an adhesive or flux to form multi-layer bumps
Data Source
AI summary
A method for forming multi-layer bumps on a substrate includes depositing an adhesive or a flux on the substrate, depositing a first metal powder on the adhesive, and melting or reflowing the adhesive and first metal powder to form first bumps. An adhesive or a flux and a second metal powder are then deposited on the first bumps, and melted to form second bumps on the first bumps to form multi-layer bumps. The multi-layer bumps are formed without the need for any wet chemicals.