Ag Alloy Bonding Wire Composition for Reliable High-Density Packaging
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Solution Overview
Problem
Ag bonding wires face challenges in high-density packaging due to low bonding reliability, spring failure, and chip damage, particularly in high-temperature high humidity environments, where they fail to maintain electrical contact and suffer from void formation and corrosion at the bonding interface, leading to reduced ball bond life and increased risk of spring failures and chip damage.
Innovation Solution
A bonding wire composition containing 0.05 to 5 at% In and/or Cd, optionally with Ni, Cu, Rh, Pd, Pt, and Au, and trace amounts of Be, B, P, Ca, Y, and Ce, with In and Cd on the surface, to enhance bonding reliability, prevent spring failures, and reduce chip damage by inhibiting Ag-Al intermetallic compound growth and improving tensile strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If Ag bonding wire is used to reduce cost compared to Au, then material cost is reduced, but bonding reliability deteriorates in high temperature high humidity environments
Solution Approach 1:
The patent applies composite materials by creating an Ag-In-Cd alloy bonding wire that combines silver with indium and cadmium elements. This composite structure leverages the low cost of Ag while In and Cd enhance bonding reliability through intermetallic compound formation, specifically Ag-In and Ag-Cd intermetallics that improve bond strength and stability in high temperature high humidity environments, thus resolving the contradiction between cost reduction and reliability maintenance.
Solution Approach 2:
The patent applies parameter changes by precisely controlling the composition parameters of the Ag-In-Cd alloy, with In content at 0.01-3 at% and Cd content at 0.01-2 at%. This compositional parameter optimization ensures that the bonding wire achieves adequate ball hardness for reliable bonding while preventing excessive hardness that would cause chip damage, thereby maintaining bonding reliability without sacrificing the cost advantage of using Ag instead of Au.
2Reliability
If alloy elements are added to Ag to improve bonding reliability, then bonding reliability is improved, but ball hardness increases causing chip damage
Solution Approach 1:
The patent applies parameter changes by precisely controlling the concentration parameters of alloying elements In and Cd within narrow ranges (In: 0.01-3 at%, Cd: 0.01-2 at%). This precise parameter control ensures that the ball hardness is enhanced sufficiently to improve bonding reliability through better bond strength, while simultaneously preventing excessive hardening that would lead to chip damage during the bonding process.
Solution Approach 2:
The patent applies local quality by creating a surface-enriched composition where In and Cd elements are concentrated at the outermost surface of the bonding wire (with In+Cd content at the surface being at least 0.5 times that in the inner portion). This local quality enhancement ensures that the bonding interface has optimal hardness and intermetallic compound formation for reliable bonding, while the bulk material maintains appropriate ductility to prevent chip damage.
3Volume of moving object
If wire diameter is reduced to accommodate high density packaging, then packaging density is improved, but wedge bondability deteriorates
Solution Approach 1:
The patent applies composite materials by formulating an Ag-In-Cd alloy that maintains adequate ductility and wedge bondability even at reduced wire diameters (15-50 μm). The In and Cd elements form intermetallic compounds that enhance bond strength at the bonding interface, compensating for the reduced wire diameter, while the overall alloy composition preserves the ductility needed for effective wedge bonding process.
Solution Approach 2:
The patent applies parameter changes by optimizing the compositional parameters of the Ag-In-Cd alloy to maintain appropriate mechanical properties at small wire diameters. The controlled addition of In (0.01-3 at%) and Cd (0.01-2 at%) ensures that even when wire diameter is reduced for high-density packaging, the bonding wire retains sufficient ductility for wedge bondability while achieving improved bond strength through intermetallic compound formation.
4Duration of action of stationary object
If In and Cd content is increased to improve bonding reliability, then ball bond life is extended, but wire strength decreases increasing spring failure risk
Solution Approach 1:
The patent applies parameter changes by precisely controlling the concentration parameters of In and Cd within optimized ranges (In: 0.01-3 at%, Cd: 0.01-2 at%). This parameter optimization ensures that sufficient intermetallic compounds (Ag-In and Ag-Cd) are formed to extend ball bond life and improve bonding reliability, while simultaneously preventing excessive alloying that would over-harden the wire and reduce ductility, thus avoiding increased spring failure risk.
Solution Approach 2:
The patent applies local quality by creating a non-uniform composition distribution where In and Cd elements are enriched at the bonding surface (surface content at least 0.5 times the inner portion content). This local quality enhancement ensures that the bonding interface has optimal intermetallic compound formation for extended ball bond life, while the bulk material maintains adequate strength and ductility to prevent spring failures during the bonding process.
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 bonding wire achieves extended ball bond life of 300 hours or more in high-density packaging, prevents spring failures, and reduces chip damage, meeting the performance requirements for high-density applications while potentially replacing Au wires with a cost-effective solution.
Implementation Method 1
enhance bonding reliability, prevent spring failures, and reduce chip damage by inhibiting Ag-Al intermetallic compound growth
Implementation Method 2
heat-melting a wire tip by arc heat input, forming a ball by surface tension
Implementation Method 3
heat-melting a wire tip by arc heat input
Implementation Method 4
pressure-bonding (hereinafter referred to as ball bonding) the ball to an electrode of a semiconductor element heated in a range of 150 to 300°C
Data Source
AI summary
The present invention provides a bonding wire which can satisfy bonding reliability, spring performance, and chip damage performance required in high-density packaging. A bonding wire contains one or more of In, Ga, and Cd for a total of 0.05 to 5 at%, and a balance being made up of Ag and incidental impurities.