Ag Bonding Wire Crystal Structure for Reverse Bonding Stability
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Solution Overview
Problem
The increasing pin count and narrowed pitch in semiconductor devices lead to issues such as leaning failures and spring failures, particularly in reverse bonding, where the low hardness of Ag or Ag alloy wires causes instability and breakage, and existing solutions have not effectively addressed both problems simultaneously.
Innovation Solution
A bonding wire with an Ag content of 90% or more, incorporating specific alloying elements like Pd, Cu, Au, Zn, Pt, Ge, Sn, Ti, and Ni, and a controlled crystal structure with a cross-section direction ratio of 10-50% and surface direction ratio of 70% or more, achieved through a drawing process with a 15.5-30.5% reduction in area and heat treatments between 300°C to 800°C, prevents fiber texture formation and enhances mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If Ag or Ag alloy bonding wire is used to reduce hardness and improve loop control, then ease of operation is improved, but reliability deteriorates due to leaning failures and spring failures
Solution Approach 1:
The patent applies parameter changes by precisely controlling the crystal grain structure parameters - specifically limiting the area ratio of elongated crystal grains to 10-50% and controlling the orientation ratio of crystal grains within 15° of the wire axis to 70% or more. This optimization of structural parameters enables Ag bonding wire to achieve both good loop control and high bond reliability, resolving the contradiction between ease of operation and reliability
Solution Approach 2:
The patent uses composite material approach by creating a controlled multi-phase crystal structure consisting of both elongated crystal grains (10-50% area ratio) and oriented crystal grains (70% or more orientation ratio). This composite crystal structure combines the benefits of elongated grains for loop control with oriented grains for bonding reliability, eliminating both leaning failures and spring failures
2Productivity
If pitch is narrowed to increase pin count, then productivity is improved, but reliability deteriorates due to leaning failures
Solution Approach 1:
The patent applies parameter changes by optimizing the crystal grain orientation parameters - specifically controlling the orientation ratio of crystal grains within 15° of the wire axis to 70% or more. This parameter optimization provides stable loop control that prevents leaning failures even when pitch is narrowed for higher pin count, enabling both productivity improvement and reliability maintenance
3Ease of operation
If reverse bonding is used to reduce loop height, then ease of operation is improved, but reliability deteriorates due to spring failures
Solution Approach 1:
The patent applies parameter changes by precisely controlling the crystal grain structure parameters - limiting elongated crystal grains to 10-50% area ratio and controlling oriented crystal grains to 70% or more orientation ratio. This optimized crystal structure eliminates spring failures in reverse bonding while maintaining low loop height, resolving the contradiction between ease of operation and reliability
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
This approach simultaneously reduces leaning and spring failures by eliminating fiber texture and optimizing crystal orientation, ensuring stable loop control and long-term reliability in high-density semiconductor packaging.
Implementation Method 1
One end of a bonding wire is formed into a ball by heating the tip of the wire to melt
Implementation Method 2
PLT 3 discloses an Ag-Au-Pd ternary alloy-based bonding wire mainly comprised of Ag. The bonding wire is heat treated for annealing before continuous die drawing
Implementation Method 3
is drawn continuously by die drawing, then is heat treated for tempering
Data Source
AI summary
Bonding wire for semiconductor device use where both leaning failures and spring failures are suppressed by (1) in a cross-section containing the wire center and parallel to the wire longitudinal direction (wire center cross-section), there are no crystal grains with a ratio a/b of a long axis "a" and a short axis "b" of 10 or more and with an area of 15 µm2 or more ("fiber texture"), (2) when measuring a crystal direction in the wire longitudinal direction in the wire center cross-section, the ratio of crystal direction <100> with an angle difference with respect to the wire longitudinal direction of 15° or less is, by area ratio, 10% to less than 50%, and (3) when measuring a crystal direction in the wire longitudinal direction at the wire surface, the ratio of crystal direction <100> with an angle difference with respect to the wire longitudinal direction of 15° or less is, by area ratio, 70% or more. During the drawing step, a drawing operation with a rate of reduction of area of 15.5% or more is performed at least once. The final heat treatment temperature and the pre-final heat treatment temperature are made predetermined ranges.