Flux-Compatible Epoxy-Phenolic Underfill for Flip-Chip
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Solution Overview
Problem
In flip-chip semiconductor assemblies, the interaction between no-clean flux residues and epoxy underfill encapsulants leads to voiding and solder extrusion, causing poor adhesion and early delamination, which affects the reliability and electrical integrity of the device.
Innovation Solution
A flux-compatible epoxy-phenolic adhesive composition comprising an epoxy component with a cycloaliphatic or alicyclic backbone, a multifunctional phenolic component, and a catalyst, such as imidazoles, is used to provide rapid curing and strong adhesion, ensuring stable thermal cycle properties and minimizing moisture absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If no-clean flux is used in flip-chip assembly, then flux residues remain on the board after solder reflow, but these residues cause voiding and solder extrusion leading to poor adhesion and early delamination
Solution Approach 1:
The patent introduces a flux residue compatible underfill composition as an intermediary substance that interacts positively with the harmful flux residues. This underfill composition contains specific components (epoxy resin, phenolic resin, and catalyst) that chemically interact with the flux residues to prevent voiding and solder extrusion, thereby mediating between the no-clean flux process and the requirement for reliable adhesion.
Solution Approach 2:
The patent modifies the chemical parameters of the underfill composition by incorporating specific ratios of epoxy resin (30-70 parts by weight), phenolic resin (10-40 parts by weight), and catalyst (1-5 parts by weight). These parameter changes enable the underfill to chemically interact with flux residues while maintaining proper adhesion properties, transforming the harmful interaction into a beneficial one.
2Stress or pressure
If epoxy underfill encapsulant is used to relieve thermomechanical stresses, then stress relief is achieved, but interaction with flux residues causes voiding and solder extrusion
Solution Approach 1:
The patent creates a composite underfill material combining epoxy resin (providing stress relief and CTE matching), phenolic resin (providing adhesion and flux residue compatibility), and catalyst (enabling curing). This composite formulation achieves both thermomechanical stress relief and flux residue compatibility simultaneously, eliminating the voiding and solder extrusion issues present in conventional epoxy underfills.
3Duration of action of stationary object
If conventional epoxy underfill is used, then thermomechanical stress is relieved, but flux residues cause early delamination
Solution Approach 1:
The phenolic resin component acts as an intermediary that chemically interacts with flux residues, preventing the harmful effects that lead to delamination. This intermediary action allows the underfill to maintain long-term operational life while resisting delamination even in the presence of no-clean flux residues.
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
The composition enables quick assembly and secure connection of semiconductor devices to circuit boards with improved thermal cycle performance and extended operational life, reducing production downtime and enhancing reliability.
Implementation Method 1
The composition includes: an epoxy component comprising an epoxy compound having a cycloaliphatic, alicyclic or mixed cycloaliphatic-aromatic, alicyclic-aromatic backbone; a phenolic component, such as multifunctional phenol; and a catalyst.
Implementation Method 2
a catalyst, such as imidazoles
Implementation Method 3
After solder reflow to attach the integrated circuit to the substrate, the gap between the integrated circuit and the organic substrate in a flip-chip assembly is filled with an underfill encapsulant or adhesive by capillary action.
Implementation Method 4
While most of the solvent of the flux boils off during the reflow process, the rosin ester and other nonvolatile residues of the solder paste constituents remain.
Implementation Method 5
A flux-compatible epoxy-phenolic adhesive composition comprising an epoxy component with a cycloaliphatic or alicyclic backbone, a multifunctional phenolic component, and a catalyst, such as imidazoles, is used to provide rapid curing and strong adhesion
Data Source
AI summary
Provided are flux-compatible epoxy-phenol adhesive compositions useful as a low gap underfill and novel phenols useful therein. The flux-compatible epoxy-phenol adhesive compositions include an epoxy component including an epoxy compound having a cycloaliphatic, alicyclic or mixed cycloaliphatic-aromatic backbone, a multifunctional phenolic component, and a catalyst. The flux-compatible compositions are useful as an underfilling sealant which (1) rapidly fills the underfill space in a semiconductor device, such as a flip chip assembly, (2) enables the device to be securely connected to a circuit board by short-time heat curing and with good productivity, and (3) demonstrates excellent solder reflow resistance.