Laser-Assisted Wirebonding Surface Conditioning
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Solution Overview
Problem
Wirebonding in microelectronics faces challenges such as damage to bond pads due to pressure and ultrasonic energy, contamination, irregularities on the bonding surface, and the formation of weak or lifted welds, which inhibit the formation of robust and uniform welds.
Innovation Solution
The use of a laser, specifically a Nd:YAG laser, for conditioning the bonding surfaces by removing contaminants and irregularities, followed by forming a free air ball and welding with minimal ultrasonic energy and pressure, to ensure improved weld formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pressure and ultrasonic energy are applied to form a weld, then weld formation is assisted, but damage to bond pads occurs
Solution Approach 1:
The bond pad surface is conditioned beforehand using laser ablation or plasma treatment to remove contaminants and oxides, creating a clean surface that promotes weld formation without requiring excessive pressure or ultrasonic energy during the actual bonding process
Solution Approach 2:
The patent replaces part of the mechanical welding process with laser heating, where a laser beam is used to locally heat the bond pad and wire bond interface, enabling weld formation through thermal energy rather than relying solely on mechanical pressure and ultrasonic vibration
2Reliability
If contaminants are present on bonding surface, then weld formation is inhibited, but cleaning processes may add complexity
Solution Approach 1:
The patent uses laser ablation where the laser beam rapidly heats and vaporizes contaminant layers on the bond pad surface, transitioning them from solid/liquid state to gas phase, thereby removing contaminants without requiring additional mechanical cleaning equipment or complex multi-step cleaning processes
Solution Approach 2:
The patent employs plasma treatment using reactive oxygen or nitrogen plasma to chemically oxidize and remove organic contaminants from the bond pad surface, creating a clean, oxide-free surface that enhances weld formation without adding mechanical complexity
3Reliability
If ultrasonic energy is applied to ensure contact, then weld formation is improved, but cracks in layers occur
Solution Approach 1:
The bond pad surface is pre-conditioned with laser ablation or plasma treatment to remove contaminants and create a clean surface, which allows weld formation to proceed with reduced ultrasonic energy input, thereby preventing cracks in the delicate low-K or ultra-low-K layers
Solution Approach 2:
The patent modifies the welding parameters by introducing laser heating, which changes the thermal state of the bond interface, allowing for lower pressure and reduced ultrasonic energy input while maintaining effective weld formation, thus protecting the integrity of sensitive layers
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 method enhances the formation of robust and uniform welds by preparing the bonding surfaces, reducing damage to delicate pads, and eliminating contaminants, while allowing for the use of various materials like gold, copper, and palladium with reduced risk of weld defects.
Implementation Method 1
conditioning the bonding surface by the application of at least one laser pulse
Implementation Method 2
a molten 'free air ball' is formed by melting the free end of the wire, held by a 'bonding head' or 'capillary', using a high voltage spark in a technique known as electronic flame-off (EFO)
Implementation Method 3
form a weld joining the wire with the bonding surface
Data Source
AI summary
The invention provides methods and systems for laser assisted wirebonding. One or more conditioning laser pulses are used to prepare a bonding surface for wirebonding by removing impurities such as residues from manufacturing processes, oxides, or irregularities on the bonding surface. Subsequently, a free air ball is brought into contact with the conditioned bonding surface to form a weld.