Heated Ultrasonic Copper Wire Bonding for Bond Pad Protection
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Solution Overview
Problem
Existing methods for establishing a permanent electrical connection between bonding wires and conductive surfaces, particularly with copper wires, face challenges such as increased mechanical stress and damage to the bond pad due to the hardness difference and require higher ultrasonic power and pressure, leading to potential material damage and reduced reliability.
Innovation Solution
A method involving heating the conductive layer and bonding wire, combined with ultrasonic energy and controlled pressure, to deform the wire and create a durable bond, using wires with a rounded cross-section of at least 125 μm diameter or a rectangular cross-section with specific dimensions, and employing a bonding device that positions and presses the wire onto the heated surface within a controlled environment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Cu-wires are used instead of Al-wires for wedge bonding, then reliability and performance are improved, but the hardness of Cu-wires requires higher ultrasonic power and pressure which may cause severe damages to the bond pad material
Solution Approach 1:
The patent changes the physical state parameters by heating the bond pad material to elevated temperatures (e.g., 100°C to 500°C) before and during the bonding process. This temperature parameter change softens the Cu-wire and reduces its hardness, allowing bonding with lower ultrasonic power and pressure, thereby preventing damage to the bond pad material while maintaining connection reliability
Solution Approach 2:
The patent applies preliminary heating to the bond pad material before the actual bonding operation. This preliminary action of heating softens the Cu-wire in advance, reducing its hardness before the bonding process begins, which prevents the need for high pressure and ultrasonic power that would otherwise damage the bond pad
2Strength
If higher pressure is applied to press Cu-wire on bond pad, then bonding strength is improved, but severe damages occur to the bond pad material
Solution Approach 1:
The patent changes the temperature parameter of the bond pad material to elevated levels (100°C to 500°C) which softens the material and reduces the required bonding pressure. This parameter change allows achieving sufficient bonding strength with lower pressure, preventing damage to the bond pad material
Solution Approach 2:
The patent uses ultrasonic vibration as the primary bonding mechanism instead of relying on high mechanical pressure. The ultrasonic energy facilitates bonding through vibrational heating and mechanical agitation at the bonding interface, allowing strong bonds to form with minimal applied pressure, thus preventing bond pad damage
3Reliability
If higher ultrasonic power is provided for Cu-wire bonding, then bonding effectiveness is improved, but the time for performing the bonding process is increased
Solution Approach 1:
The patent changes the temperature parameter by heating the bond pad material before and during bonding. This pre-heating softens the Cu-wire and reduces its hardness, enabling more efficient bonding with lower ultrasonic power requirements and shorter bonding times, thus improving effectiveness without increasing process time
Solution Approach 2:
The patent applies preliminary heating to the bond pad material before the bonding operation. This preliminary action reduces the ultrasonic power needed during bonding by softening the Cu-wire in advance, thereby achieving effective bonding faster and reducing overall process time
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 reduces mechanical stress, enhances bond reliability, and maintains the quality of the connection comparable to conventional methods while minimizing material commingling and surface oxidation, resulting in a stable and durable bond connection.
Implementation Method 1
heating a first electrically conductive layer that is to be electrically contacted, and that is arranged on a first element, and pressing a first end of a bonding wire on the first electrically conductive layer
Implementation Method 2
pressing a first end of a bonding wire on the first electrically conductive layer by exerting pressure to the first end of the bonding wire
Implementation Method 3
deforming the first end of the bonding wire
Implementation Method 4
exposing the first end of the bonding wire to ultrasonic energy, thereby deforming the first end of the bonding wire and creating a permanent substance-to-substance bond
Data Source
Figure 1~4
Figure 5A~7
Figure 8~10
AI summary
A method comprises heating a first electrically conductive layer (14) that is to be electrically contacted, and that is arranged on a first element (10), and pressing a first end (22) of a bonding wire (20) on the first electrically conductive layer (14) by exerting pressure to the first end (22) of the bonding wire (20), and further by exposing the first end (22) of the bonding wire (20) to ultrasonic energy, thereby deforming the first end (22) of the bonding wire (20) and creating a permanent substance-to-substance bond between the first end (22) of the bonding wire (20) and the first electrically conductive layer (14). The bonding wire (20) either comprises a rounded cross section with a diameter (d1) of at least 125µm or a rectangular cross section with a first width (w1) of at least 500µm and a first height (h1) of at least 50µm.