Tight Pitch Solder Bumps via Thick Resist and Ozone Stripping
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional positive photoresist techniques limit the pitch of solder bumps on integrated circuits due to overplating requirements, making it difficult to achieve smaller sizes, while negative photoresists are challenging to strip and thus not commonly used for solder bump formation.
Innovation Solution
A method involving a resist layer on an integrated circuit, forming holes, filling them with conductive material, and using a stripping solution containing acetic anhydride and ozone to expose the connective elements, allowing for the use of thicker photoresist materials and tighter pitch solder bumps without overplating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional positive photoresist is used to mask the IC and define solder deposition regions, then the photoresist can be easily stripped, but the limited thickness requires overplating which limits the pitch of solder bumps
Solution Approach 1:
The patent changes the thickness parameter of the photoresist layer from conventional thin layers to thicker layers (e.g., 5-20 micrometers). This allows sufficient solder volume to be deposited within the holes without requiring overplating, thereby enabling tighter pitch solder bumps while maintaining easy stripping characteristics of positive photoresist
Solution Approach 2:
The patent transitions from a 2D surface overplating approach to a 3D vertical hole-filling approach. By forming holes through the thick photoresist and filling them with solder, the solder is contained vertically within the hole rather than spreading radially outward, eliminating the overplating interference problem and enabling tighter pitch
2Manufacturing precision
If negative photoresist is used to deposit larger volumes of solder without overplating, then tighter pitch solder bumps can be formed, but the photoresist is difficult to strip
Solution Approach 1:
The patent introduces a specialized stripping solution containing ozone and acetic acid as an intermediary substance that enables the stripping of negative photoresist. The ozone oxidizes the photoresist material, making it soluble in the acetic acid-based solution, thereby achieving easy stripping while maintaining the ability to form tight pitch solder bumps with thick photoresist
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
Enables the formation of connective elements with tighter pitches and greater material flexibility, simplifying the fabrication process, reducing equipment needs, and providing a cost-effective, less corrosive stripping solution that effectively removes photoresist without damaging underlying metal layers.
Implementation Method 1
stripping at least a portion of the resist layer using a stripping solution containing acetic anhydride and ozone
Data Source
AI summary
Methods for forming connective elements on integrated circuits for packaging applications are provided herein. In some embodiments, a method of forming connective elements on an integrated circuit for flipchip packaging may include providing a resist layer on the integrated circuit; forming a plurality of holes through the resist layer; filling the plurality of holes with conductive material; and stripping at least a portion of the resist layer using a stripping solution containing acetic anhydride and ozone to expose the connective elements.