Bond Wire Microstructure Control via Deformation and Thermal Treatment
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Solution Overview
Problem
The ultrasonic bonding process for metal-semiconductor connections results in a microstructure with high angle grain boundaries, leading to reliability issues due to crack propagation and creep-fatigue at high temperatures, and ductility issues at low temperatures, as the recrystallization process is uncontrolled and non-optimized.
Innovation Solution
A method involving controlled deformation and temperature treatment to increase dislocation density and grain size in the bond region, using ultrasound waves at frequencies lower than 20kHz and subsequent thermal treatment to enhance hardness and reliability, specifically by deforming the bond region and then raising the temperature to reduce dislocation density and increase grain size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ultrasonic bonding process is used to connect wire to semiconductor chip, then electrical and mechanical connection is achieved, but microstructure contains high angle grain boundaries leading to reliability issues at high temperatures
Solution Approach 1:
The patent applies preliminary deformation before final bonding to pre-establish a favorable microstructure. By deforming the wire end before ultrasonic bonding, the material undergoes plastic deformation that creates a denser, more stable microstructure with reduced high-angle grain boundaries, preventing reliability issues before they occur during high-temperature operation
Solution Approach 2:
The patent changes physical parameters of the bonding process, specifically applying controlled deformation strain and adjusting ultrasonic bonding parameters. This transforms the microstructure from an unstable state with high-angle grain boundaries to a stable state with reduced defect density, improving reliability at high temperatures
2Ease of manufacture
If recrystallization process occurs during ultrasonic bonding, then softening and deformation are achieved, but uncontrolled recrystallization creates non-optimized microstructure with reliability and ductility issues
Solution Approach 1:
The patent implements feedback control by monitoring bonding parameters and adjusting deformation and ultrasonic energy input in real-time. This controlled approach manages the recrystallization process to achieve the desired balance between softening for bonding and maintaining microstructural stability for reliability
Solution Approach 2:
The patent makes the bonding process dynamic by applying controlled deformation during ultrasonic bonding rather than static conditions. This dynamic approach allows real-time control over microstructure evolution, transforming the uncontrolled recrystallization into a controlled process that produces reliable bonds
3Strength
If high dislocation density is present in bond region, then deformation capability is improved, but hardness increases and reliability decreases due to crack propagation
Solution Approach 1:
The patent applies local quality by creating different microstructural zones within the bond region. The deformed zone has controlled dislocation density for deformation capability, while the bonded interface maintains optimal properties for reliability. This spatial differentiation of material properties resolves the contradiction between deformation strength and reliability
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 method improves bond reliability by increasing hardness and grain size, reducing high angle grain boundaries, and enhancing resistance to thermal cycles, thus addressing the limitations of the state-of-the-art ultrasonic bonding process.
Implementation Method 1
introduces ultrasonic waves (frequency more than 20 kHz, typically 60 kHz or 110 kHz) to make the electrical connection
Implementation Method 2
applies pressure to deform the wire on the metallization surface or lead frame such as obtaining conforming surfaces
Implementation Method 3
raising the temperature to reduce dislocation density and increase grain size
Data Source
Figure 1~2
Figure 3(a)~3(c)
Figure 4(a)~4(c)
AI summary
The invention relates to producing a semiconductor chip-metal wire bond, by performing the steps of bonding a wire having a metal body to the semiconductor chip so as to connect the wire to the semiconductor chip, the bond metal having a polycrystalline microstructure, and deforming a bonding region of the metal body in contact with to the semiconductor chip, the deformed bonding region being characterized by a relative cross section area change given by ε=A0−AfA0, where Af is a final cross section area and A0 is an initial cross section area, the deformation involving an increase of a dislocation density in the microstructure of at least a portion of the bonding region.