Pd-Alloy Bonding Wire for Semiconductor Reliability
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Solution Overview
Problem
Copper bonding wires exhibit reliability issues in high-humidity and thermal cycle tests, leading to decreased bonding strength and increased electric resistance, limiting their use in semiconductor applications, especially when bonded to aluminum electrodes.
Innovation Solution
A copper alloy bonding wire with a composition of 0.13 to 1.15% by mass Pd, combined with Ag and Au, and containing Ti, B, and P, is developed to enhance high-humidity heating reliability and thermal cycle performance, featuring a specific crystal grain size and copper oxide film thickness to improve bonding strength and stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a copper bonding wire is used to improve bonding reliability in high-temperature environments, then the bonding reliability is improved, but the wire becomes harder causing chip damages during bonding
Solution Approach 1:
The patent changes the chemical composition parameters of the copper wire by adding specific amounts of Pd (0.01-1.0 wt%), Ag (0.01-1.0 wt%), and Au (0.01-1.0 wt%). This compositional modification adjusts the hardness parameter to be lower than pure copper while maintaining the bonding reliability improvement against aluminum electrodes at high temperatures.
Solution Approach 2:
The patent creates a composite copper alloy material combining Cu with Pd, Ag, and Au elements. This composite structure leverages the beneficial properties of each element: Cu provides conductivity and cost-effectiveness, while the added elements modify hardness and improve intermetallic compound growth resistance, achieving a balance between bonding reliability and wire softness.
2Reliability
If a copper bonding wire is used to reduce cost and improve conductivity, then cost is reduced and conductivity is improved, but the wire exhibits reliability issues in high-humidity and thermal cycle tests
Solution Approach 1:
The patent modifies the chemical composition parameters by adding Pd, Ag, and Au elements to copper. This compositional change fundamentally alters the material's response to high-humidity and thermal cycling conditions, forming protective or stable intermetallic compounds that prevent degradation mechanisms affecting pure copper wires.
Solution Approach 2:
The added Pd, Ag, and Au elements act as intermediaries that modify the interaction between copper and the corrosive environment. These elements form stable compounds or protective layers that mediate the harmful effects of high humidity and thermal cycling, preventing direct degradation of the copper-aluminum bonding interface.
3Reliability
If a copper bonding wire is used to improve high-temperature reliability, then the intermetallic compound growth speed is reduced, but the wedge bonding production margin is smaller
Solution Approach 1:
The patent optimizes the compositional parameters of Pd, Ag, and Au additions to achieve a balance between intermetallic compound growth control and wedge bonding performance. The specific concentration ranges are designed to slow down harmful intermetallic growth at the bonding interface while maintaining sufficient ductility and bonding characteristics for productive wedge bonding 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
The copper alloy bonding wire demonstrates improved long-term reliability, extended life in high-humidity conditions, and enhanced thermal cycle resistance, allowing for more widespread use in semiconductor applications, including fine pitch bonding, with stable wedge bondability and reduced chip damage.
Implementation Method 1
a speed at which a Cu—Al based intermetallic compound grows in a copper/aluminum bonded portion is as slow as or slower than 1/10 of a speed at which an Au—Al based intermetallic compound grows
Implementation Method 2
A front end of the bonding wire is then heated and melted by means of an arc heat input, thereby forming a ball due to a surface tension
Implementation Method 3
forming a ball due to a surface tension
Implementation Method 4
the ball thus formed is press-bonded to the electrode on the semiconductor element that has been heated at 150 to 300° C
Implementation Method 5
bonded through a thermal compressive bonding technique with the aid of ultrasound
Implementation Method 6
the bonding wire is directly wedge-bonded to an external lead side through an ultrasound compressive bonding
Data Source
AI summary
The present invention is a copper-based bonding wire for use in a semiconductor element. The bonding wire of the present invention can be manufactured with an inexpensive material cost, and has a superior PCT reliability in a high-humidity/temperature environment. Further, the bonding wire of the present invention exhibits: a favorable TCT reliability through a thermal cycle test; a favorable press-bonded ball shape; a favorable wedge bondability; a favorable loop formability, and so on. Specifically, the bonding wire of the present invention is a copper alloy bonding wire for semiconductor manufactured by drawing a copper alloy containing 0.13 to 1.15% by mass of Pd and a remainder comprised of copper and unavoidable impurities.