Polymer-Based Semiconductor Packaging Without Flux Cleaning
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Solution Overview
Problem
The challenge in semiconductor packaging is the need for flux cleaning after soldering, which is particularly difficult in fine-pitch WLCSP packaging and requires expensive fine-pitch cleaning equipment, increasing costs and complicating the assembly process.
Innovation Solution
The method involves using polymer-based solder paste to form fine-pitch solder joints, where a post-soldering residue encapsulates the lower portion of each solder joint, allowing for underfill injection without flux cleaning, and enabling simultaneous assembly of components without solder balls/bumps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional solder paste is used for fine-pitch WLCSP packaging, then solder joints can be formed, but flux cleaning is required which increases process costs and requires expensive cleaning equipment
Solution Approach 1:
The patent extracts and removes the flux component from the solder paste formulation, replacing it with polymer-based materials that provide soldering functionality without requiring subsequent cleaning operations. This eliminates the harmful flux residues that necessitate expensive cleaning equipment and complex post-soldering processes.
Solution Approach 2:
The patent changes the chemical composition parameters of the solder paste by substituting traditional flux materials with polymer-based materials. This parameter change transforms the paste from a conventional flux-containing formulation to a flux-free polymer-based formulation that produces no harmful residues requiring cleaning.
2Reliability
If flux cleaning is performed after soldering, then solder joints are formed, but the process becomes complex and costly due to equipment requirements
Solution Approach 1:
The patent removes the flux cleaning step entirely from the manufacturing process by using polymer-based solder paste that does not produce harmful residues. This extraction of the cleaning operation eliminates the need for complex cleaning equipment and simplifies the overall manufacturing process while maintaining reliable solder joint formation.
Solution Approach 2:
The polymer-based solder paste performs the cleaning function inherently during the reflow process itself, as the polymer materials volatilize or decompose without leaving residues. This self-service mechanism eliminates the need for separate cleaning operations and complex equipment.
3Manufacturing precision
If traditional solder paste is used, then solder joints can be formed, but post-soldering residue requires cleaning that increases process costs
Solution Approach 1:
The patent changes the material composition parameter of the solder paste from flux-based to polymer-based materials. This parameter change fundamentally alters the post-soldering behavior, transforming the paste from one that leaves harmful residues requiring cleaning to one that volatilizes or decomposes cleanly, thereby eliminating flux residue loss.
Solution Approach 2:
The patent converts the potential harm of residue formation into a benefit by using polymer materials that decompose or volatilize during reflow, leaving no harmful residues. The materials that would traditionally be considered problematic (polymer decomposition products) are selected to be benign and eliminate the need for cleaning operations.
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 eliminates the need for expensive fine-pitch cleaning equipment, reduces process costs, and allows for simultaneous assembly of various components, resulting in a more efficient and cost-effective semiconductor packaging process.
Implementation Method 1
reflowing the polymer-based solder paste to form a plurality of solder joints between the substrate and the semiconductor die
Implementation Method 2
applying an underfill between the substrate and the semiconductor die to encapsulate an upper portion of the solder joint
Data Source
AI summary
A method for fabricating a semiconductor package includes applying polymer-based solder paste onto a substrate; bringing a plurality of solder bumps on a semiconductor die into contact with the polymer-based solder paste on the substrate; reflowing the polymer-based solder paste to form a plurality of solder joints between the substrate and the semiconductor die, wherein a post-soldering residue is produced to encapsulate a lower portion of each solder joint; and applying an underfill between the substrate and the semiconductor die to encapsulate an upper portion of the solder joint.