Waterfall Wire Bonding for Semiconductor Devices
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Solution Overview
Problem
Conventional wire bonding processes face challenges in efficiently and reliably bonding semiconductor components due to high forces that can cause damage and defects, such as cratering or cracking, and require multiple steps and conductive bumps, which increase fabrication time and costs.
Innovation Solution
The waterfall wire bonding process uses a capillary with a large approaching angle to apply force and ultrasonic energy at a lower temperature, forming a continuous bond without breaking the wire, reducing stress on bonding pads and eliminating the need for conductive bumps, allowing for a more uniform stress distribution and improved bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional wire bonding processes use high forces to create ball bonds and wedge bonds, then bonding strength is achieved, but defects such as cratering or cracking occur and fabrication time increases due to multiple steps
Solution Approach 1:
The patent changes the bonding parameters by using lower forces combined with elevated temperature (e.g., 150-200°C) and ultrasonic energy. This parameter transformation allows bonding to occur without the high forces that cause cratering and cracking, while the temperature facilitates material flow and bonding at reduced force levels, thereby maintaining bonding strength while eliminating defects
Solution Approach 2:
The patent employs periodic ultrasonic energy application during the bonding process. The ultrasonic vibrations are applied in controlled cycles that facilitate material diffusion and bonding while preventing excessive force concentration. This periodic action enables reliable bonding without the continuous high force that leads to structural defects
2Reliability
If conventional wire bonding uses multiple steps including ball bonding and wedge bonding with conductive bumps, then electrical coupling is achieved, but fabrication time and process complexity increase
Solution Approach 1:
The patent merges the ball bonding and wedge bonding steps into a single unified bonding operation. By using a specialized capillary structure with a beveled tip, the wire is directly bonded to the bonding pad in one continuous action without requiring separate ball formation and wedge bonding steps, or the use of conductive bumps, thereby reducing process complexity and increasing fabrication throughput while maintaining electrical coupling reliability
Solution Approach 2:
The patent performs preliminary preparation of the wire end and bonding surface before the actual bonding operation. The wire is pre-positioned and the capillary is pre-aligned at the optimal angle, allowing the bonding to proceed in a single efficient motion without requiring multiple corrective steps or intermediate structures like conductive bumps, thus improving productivity without compromising coupling reliability
3Strength
If conventional wire bonding applies high forces to the wire and bonding pad, then bonding is achieved, but stress concentration causes damage to bonding pads and reduces process reliability
Solution Approach 1:
The patent transforms the bonding parameters from high-force/room-temperature to lower-force/elevated-temperature regime. The increased temperature reduces material yield strength and facilitates plastic flow, allowing bonding to occur at lower forces that do not concentrate stress and cause damage to the bonding pad structure, while still achieving strong bonds through enhanced material diffusion
Solution Approach 2:
The patent introduces elevated temperature as an intermediary that facilitates bonding at lower forces. The heat acts as a mediator that softens the materials, enabling them to bond under reduced stress conditions. This intermediary parameter allows the bonding process to proceed without the harmful stress concentration that would otherwise be necessary to achieve adequate bonding strength
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 process reduces the risk of defects, decreases fabrication time, and enhances bonding strength while maintaining throughput, offering a 22%-64% increase in units per hour for semiconductor devices with improved reliability and cost-effectiveness.
Implementation Method 1
a high-voltage electric charge is applied to the wire from a transducer associated with the capillary tip. The electric charge melts the wire at the tip
Implementation Method 2
the wire forms into a ball owing to the surface tension of the molten metal
Implementation Method 3
ultrasonic energy is applied by the transducer. The combined heat, pressure, and ultrasonic energy create a weld between the copper or gold ball and the bonding surface
Implementation Method 4
The bonding surface can also be heated to facilitate bonding
Data Source
AI summary
A wire bonded structure for a semiconductor device is disclosed. The wire bonded structure comprises a bonding pad; and a continuous length of wire mutually diffused with the bonding pad, the wire electrically coupling the bonding pad with a first electrical contact and a second electrical contact different from the first electrical contact.