Pd-Coated Cu Bonding Wire Ball Formation
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Solution Overview
Problem
Pd-coated Cu bonding wires experience uneven Pd distribution during ball formation, leading to strength degradation and increased electrical resistance when formed in non-oxidizing atmospheres.
Innovation Solution
A ball forming method using a non-oxidizing atmosphere gas containing hydrocarbon, which generates heat through arc discharges, ensuring uniform heat transmission and improved Pd coverage on the ball surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a ball portion is formed on the tip of the Pd-coated Cu bonding wire in non-oxidizing atmosphere gas (pure nitrogen, argon, or nitrogen containing 5 vol% hydrogen), then oxidation of the ball portion is prevented, but Pd distribution becomes uneven, producing parts not coated with Pd on the ball surface
Solution Approach 1:
The invention changes the chemical composition parameter of the non-oxidizing atmosphere gas by adding hydrocarbon (0.1-10 vol%) to the base gas (nitrogen or argon with hydrogen). This parameter modification alters the arc discharge characteristics and heat transmission properties, enabling uniform Pd distribution while maintaining oxidation prevention.
Solution Approach 2:
Hydrocarbon acts as an intermediary substance in the atmosphere gas that mediates between the arc discharge energy and the wire tip melting process. The hydrocarbon components facilitate more uniform heat transmission during arc discharge, which in turn produces uniform Pd distribution on the ball surface while the non-oxidizing nature of the gas mixture continues to prevent oxidation.
2Object-affected harmful factors
If conventional non-oxidizing atmosphere gas is used for ball formation, then oxidation is prevented, but bonding strength and electrical resistance are degraded due to uneven Pd coverage
Solution Approach 1:
By modifying the atmospheric gas composition to include hydrocarbon within specific concentration ranges (0.1-10 vol%), the invention optimizes the heat transmission characteristics during arc discharge. This leads to more uniform melting and Pd distribution, thereby improving bonding strength and electrical resistance while the non-oxidizing nature of the gas mixture maintains oxidation prevention.
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 method achieves improved Pd coverage and sphericity of the ball portion, enhancing the bonding strength and electrical reliability of Pd-coated Cu bonding wires.
Implementation Method 1
the hydrocarbon in the non-oxidizing atmosphere gas generates heat as a result of arc discharges
Implementation Method 2
heat is transmitted more uniformly to surroundings of the wire tip
Implementation Method 3
forming a free air ball (hereinafter also referred to simply as a 'ball portion' or 'FAB') by surface tension
Data Source
AI summary
The present invention provides a ball forming method for forming a ball portion at a tip of a bonding wire which includes a core material mainly composed of Cu, and a coating layer mainly composed of Pd and formed over a surface of the core material, wherein the ball portion is formed in non-oxidizing atmosphere gas including hydrocarbon which is gas at room temperature and atmospheric pressure, the method being capable of improving Pd coverage on a ball surface in forming a ball at a tip of the Pd-coated Cu bonding wire.