Cu Alloy Bonding Wire with Pd Coating for High-Temperature Reliability
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Solution Overview
Problem
Conventional Cu bonding wires with Pd coating layers fail to provide sufficient bonding reliability in high-temperature and high-humidity environments, particularly in on-vehicle devices, where the bonding longevity of ball bonded parts is inadequate, as evidenced by HAST tests showing less than 100 hours of reliability.
Innovation Solution
A Cu alloy bonding wire with a Pd coating layer containing Ga and/or Ge, along with an alloy skin layer of Au and Pd, and optionally including Ni, Ir, Pt, B, P, or Mg, to enhance bonding reliability by reducing intermetallic compound formation and improving oxidation resistance and adhesiveness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-purity Cu is used as bonding wire material, then cost is reduced and electrical conductivity is improved, but oxidation resistance deteriorates and bonding reliability in high-temperature high-humidity environment deteriorates
Solution Approach 1:
A Pd coating layer is introduced as an intermediary between the Cu core material and the external environment. This Pd layer serves as a protective barrier that prevents oxidation of the Cu core while maintaining electrical conductivity and bonding performance. The coating thickness is controlled at 0.01 to 0.05 μm to provide adequate protection without excessive complexity.
Solution Approach 2:
The bonding wire is designed as a composite structure consisting of a Cu core material (99.99% purity) and a Pd coating layer. This composite structure combines the advantages of Cu (low cost, high conductivity) with the advantages of Pd (oxidation resistance, good bondability), resolving the contradiction between cost reduction and oxidation resistance.
2Reliability
If Ga and Ge are added to Cu alloy, then bonding longevity in HAST is improved, but manufacturing precision may deteriorate due to alloying complexity
Solution Approach 1:
The concentrations of Ga and Ge are precisely controlled within narrow ranges (0.003-0.015 mass% each) to achieve the desired bonding longevity improvement while maintaining manufacturing feasibility. This precise parameter control allows for improved reliability without excessive manufacturing complexity.
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 proposed bonding wire configuration significantly improves bonding reliability in high-temperature and high-humidity conditions by reducing the formation of corrosive intermetallic compounds and enhancing the structural integrity of the bonding interface, achieving longer bonding longevity and improved wedge bondability.
Implementation Method 1
heating and melting a wire tip with arc heat input
Implementation Method 2
forming a ball (FAB: free air ball) through surface tension
Implementation Method 3
Cu has the drawback of being more susceptible to oxidation than Au and has problems in that bonding reliability, ball formability, and wedge bondability are inferior. As a method for preventing surface oxidation of the Cu bonding wire, a structure that coats a surface of a Cu core material with a metal such as Au, Ag, Pt, Pd, Ni, Co, Cr, or Ti is developed
Data Source
AI summary
There is provided a Cu bonding wire having a Pd coating layer on a surface thereof, that improves bonding reliability of a ball bonded part in a high-temperature, high-humidity environment and is suitable for on-vehicle devices. The bonding wire for a semiconductor device includes a Cu alloy core material and a Pd coating layer formed on a surface of the Cu alloy core material, and the bonding wire contains Ga and Ge of 0.011 to 1.2% by mass in total. With this configuration, it is able to increase bonding longevity of the ball bonded part in the high-temperature, high-humidity environment, and thus to improve the bonding reliability. The thickness of the Pd coating layer is preferably 0.015 to 0.150 µm. When the bonding wire further contains one or more elements of Ni, Ir, and Pt in an amount, for each element, of 0.011 to 1.2% by mass, it is able to improve the reliability of the ball bonded part in a high-temperature environment at 175°C or more. When an alloy skin layer containing Au and Pd is further formed on a surface of the Pd coating layer, wedge bondability improves.