Coated Silver Wire for Air Atmosphere Ball Formation
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Solution Overview
Problem
Existing silver or silver alloy wires used in electronics and microelectronics face challenges in forming axi-symmetrical free air balls (FABs) without inert gas purging, and they require improved properties such as bondability, corrosion resistance, and a wide stitch bonding window.
Innovation Solution
A coated wire with a silver or silver alloy core, coated with a 1 to 1000 nm thick layer of gold or palladium, or a double-layer coating of nickel and gold, optimized to achieve axi-symmetrical FAB formation under air atmosphere, enhanced bondability, and improved corrosion resistance, with specific composition and annealing processes to ensure reproducibility and performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silver or silver alloy wires are used without coating, then cost is reduced and electrical conductivity is improved, but corrosion resistance deteriorates and FAB formation under air atmosphere becomes difficult
Solution Approach 1:
The patent applies composite material structure by combining silver core with gold or palladium coating layers. The silver core provides excellent electrical conductivity and cost benefits, while the gold or palladium coating provides superior corrosion resistance and enables reliable FAB formation under air atmosphere. This composite structure resolves the contradiction by integrating materials with complementary properties.
Solution Approach 2:
The patent uses a thin coating layer (1-1000 nm) of expensive gold or palladium on a silver core, where the coating serves as a protective sacrificial layer that prevents corrosion of the bulk silver material. The thin coating minimizes cost impact while providing sufficient protection.
2Ease of operation
If silver wires are used without inert gas purging, then process complexity is reduced, but FAB formation quality deteriorates due to oxidation
Solution Approach 1:
The gold or palladium coating is applied in advance to the silver wire surface to prevent oxidation during the wire bonding process. This preliminary protective action eliminates the need for inert gas purging while maintaining high FAB formation quality, as the coating acts as a barrier against atmospheric oxidation during ball formation.
3Reliability
If coating layer thickness is increased, then corrosion resistance is improved, but wire diameter increases and bondability may deteriorate
Solution Approach 1:
The patent optimizes the coating layer thickness to a specific range of 1-1000 nm, which provides sufficient corrosion protection while maintaining adequate bondability. This parameter optimization balances the competing requirements by finding the threshold where the coating is thick enough to protect but thin enough to allow effective ultrasonic bonding.
4Strength
If silver alloy with doping elements is used, then mechanical properties are improved, but electrical resistivity increases
Solution Approach 1:
The patent uses localized doping with specific elements (calcium, nickel, platinum, copper, rhodium, or ruthenium) at controlled concentrations (30-3000 ppm) to enhance mechanical properties such as strength and ductility, while the overall silver matrix maintains low electrical resistivity. The doping elements are distributed locally to achieve mechanical reinforcement without significantly impacting bulk electrical conductivity.
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 coated wire enables the formation of axi-symmetrical FABs under air atmosphere without inert gas purging, offering improved bondability, corrosion resistance, and a wide process window for wire bonding applications, ensuring high reproducibility and performance.
Implementation Method 1
The coated wire enables the formation of axi-symmetrical FABs under air atmosphere without inert gas purging, offering improved bondability, corrosion resistance
Implementation Method 2
with specific composition and annealing processes to ensure reproducibility and performance
Implementation Method 3
A coated wire with a silver or silver alloy core, coated with a 1 to 1000 nm thick layer of gold or palladium
Data Source
AI summary
A wire comprising a wire core with a surface, the wire core having a coating layer superimposed on its surface, wherein the wire core includes: (a) pure silver consisting of silver and further components; or (b) doped silver consisting of silver, at least one doping element, and further components; or (c) a silver alloy consisting of silver, palladium and further components; or (d) a silver alloy consisting of silver, palladium, gold, and further components; or (e) a doped silver alloy consisting of silver, palladium, gold, at least one doping element, and further components, wherein the individual amount of any further component is less than 30 wt.-ppm and the individual amount of any doping element is at least 30 wt.-ppm, and the coating layer is a single-layer of gold or palladium or a double-layer comprised of an inner layer of nickel or palladium and an adjacent outer layer of gold.