Cu Alloy Bonding Wire Microstructure for Loop Straightness
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Solution Overview
Problem
Bare Cu wires used in high-density semiconductor devices face challenges in maintaining loop straightness, resisting deformation during resin sealing, and ensuring long-term service life, particularly in high-temperature storage tests, due to issues with crystal grain orientation and deformation under ultrasonic bonding processes.
Innovation Solution
A Cu alloy bonding wire with specific crystal orientation abundance ratios and additional elements like Ni, Pd, Pt, P, In, Ga, Ge, and Ag, optimized to improve loop straightness, reduce neck portion damage, and enhance ball bond area life, by controlling crystal orientations and grain sizes to minimize plastic anisotropy and promote isotropic deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high ultrasonic wave output is used to obtain bonding strength in wedge bond areas, then bonding strength is improved, but loop straightness deteriorates due to bending caused by ultrasonic waves
Solution Approach 1:
The patent applies parameter changes by precisely controlling the crystal grain size (5 μm or less) and crystal orientation (〈100〉direction alignment) of the Cu wire. This microstructural parameter control enables the wire to achieve adequate bonding strength through controlled deformation during the scrub process, rather than relying on high ultrasonic wave output, thereby preventing loop bending while maintaining bonding strength.
2Productivity
If the wire diameter is reduced to 25 μm or less to achieve high packaging density, then packaging density is improved, but loop straightness deteriorates due to reduced loop portion strength
Solution Approach 1:
The patent applies parameter changes by controlling the crystal grain size to 5 μm or less and ensuring crystal orientation with 〈100〉direction alignment in the wire longitudinal direction. This microstructural parameter control compensates for the reduced cross-sectional area of thin wires (25 μm or less), providing sufficient strength to maintain loop straightness while enabling high packaging density through smaller wire diameter.
3Shape
If the aspect ratio of crystal grains on the skin layer surface is increased to 3 or more to improve loop straightness, then loop straightness is improved, but resistance to deformation during resin sealing deteriorates
Solution Approach 1:
The patent applies parameter changes by controlling both crystal grain size (5 μm or less) and crystal orientation (〈100〉direction alignment). This dual parameter control achieves loop straightness through isotropic deformation characteristics while maintaining adequate deformation resistance during resin sealing, overcoming the limitation of aspect ratio-based solutions that compromise strength.
4Ease of manufacture
If bare Cu wires are used to reduce cost, then manufacturing cost is reduced, but oxidation resistance and bondability deteriorate
Solution Approach 1:
The patent applies the inert atmosphere principle by specifying that the Cu wire surface is covered with an organic substance film formed in an inert or reducing atmosphere. This protective film prevents oxidation of the Cu wire while maintaining the cost advantage of using bare Cu wires instead of coated wires, thereby improving oxidation resistance without sacrificing manufacturing cost benefits.
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 solution effectively maintains high loop straightness, reduces neck portion damage, and extends ball bond area life to meet the performance requirements of high-density semiconductor devices, ensuring reliable operation under severe conditions.
Implementation Method 1
In the wedge bonding of bare Cu wires, an operation called a scrub, which vibrates a stage at a low frequency, is often used together while the wire is pressed by a capillary. The scrub promotes the deformation of the wire and is effective for improving the bonding strength of the wedge bond areas.
Implementation Method 2
A bonding process for a bonding wire involves heat-melting a wire tip by arc heat input, forming a ball (FAB: Free Air Ball) by surface tension
Implementation Method 3
heat-melting a wire tip by arc heat input, forming a ball (FAB: Free Air Ball) by surface tension
Implementation Method 4
pressure-bonding a ball portion (hereinafter referred to as ball bonding) to an electrode of a semiconductor element heated in a range of 150 to 300°C
Data Source
Figure 1
Figure 2A~2B
Figure 3
AI summary
It is an object to provide a Cu alloy bonding wire for a semiconductor device that can satisfy required performance in high-density LSI applications. In the Cu alloy bonding wire for a semiconductor device according to the present invention, each of abundance ratios of crystal orientations <100>, <110> and <111> having an angular difference of 15 degrees or less from a direction perpendicular to one plane including a wire center axis out of crystal orientations on a wire surface is 3% or more and less than 27% in average area percentage.