Copper Wirebonding Interface Area Expansion via Scrubbing
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Solution Overview
Problem
The existing wire bonding process using copper bonding wires often results in insufficient bonding strength between the copper bonding wire and the substrate pad, leading to potential peeling off during manufacturing or transportation, due to a small connecting area, which restricts the size of chip pads that can utilize copper wires effectively.
Innovation Solution
A method involving a bonding wire with a fishtail region that includes at least one scrubbing protrusion, formed by a scrubbing process after bonding, to increase the interface area between the bonding wire and the substrate pad, enhancing bonding strength, and a molding compound to seal the package.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a copper bonding wire is used to reduce cost and improve conductivity, then the wire diameter can be reduced and heat dissipation improved, but the bonding strength becomes insufficient due to small connecting area
Solution Approach 1:
The bonding wire end is formed into a spherical ball shape through spheroidization treatment. This curved spherical structure increases the contact area with the substrate pad compared to a flat end, thereby improving bonding strength and reliability while maintaining the small wire diameter advantage of copper wires
Solution Approach 2:
The surface roughness of the bonding wire is controlled within a specific range (Ra 0.03-0.1 μm) through parameter optimization. This parameter change in surface characteristics increases the effective bonding area and improves adhesion between the copper wire and substrate pad, resolving the bonding strength issue
2Area of stationary object
If the chip pad size is reduced to improve integration, then the device size is reduced, but the bonding strength becomes insufficient due to limited pad area
Solution Approach 1:
The spherical ball shape of the bonding wire end is specifically designed to match the reduced pad size. The curved surface of the sphere distributes the bonding pressure more effectively across the small pad area, maintaining adequate bonding strength even when the chip pad area is minimized for high integration
Solution Approach 2:
The surface roughness parameter (Ra 0.03-0.1 μm) is optimized to maximize the effective bonding area on small pads. This controlled surface morphology ensures sufficient mechanical interlocking and adhesion strength even when the overall pad dimensions are reduced
3Device complexity
If a conventional bonding process is used to simplify manufacturing, then the process complexity is reduced, but the bonding strength becomes insufficient leading to peeling during transportation
Solution Approach 1:
The bonding wire undergoes preliminary spheroidization treatment and surface roughness control before the actual bonding process. These preliminary actions prepare the wire in advance to achieve optimal bonding characteristics, ensuring sufficient bonding strength that prevents peeling during subsequent transportation and assembly operations
Solution Approach 2:
Specific parameter ranges are established for the bonding process (surface roughness Ra 0.03-0.1 μm, spherical ball diameter 3-10 μm) that can be implemented using conventional equipment. These parameter changes enable improved bonding strength without significantly increasing manufacturing process complexity
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 scrubbing process increases the bonding strength by expanding the interface area between the bonding wire and the substrate pad, reducing the likelihood of peeling and improving the reliability of the semiconductor package.
Implementation Method 1
The second bond portion comprises a fishtail region which comprises at least one scrubbing protrusion being integrally formed thereon
Implementation Method 2
The molding compound seals the chip and the bonding wire and covers the carrier
Data Source
AI summary
In a method of manufacturing a semiconductor package including a wire binding process, a first end of the bonding wire is bonded to a first pad so as to form a first bond portion. A second end of the bonding wire is bonded to a second pad, wherein an interface surface between the bonding wire and the second pad has a first connecting area. The bonded second end of the bonding wire is scrubbed so as to form a second bond portion, wherein a new interface surface between the bonding wire and the second pad has a second connecting area larger than the first connecting area. A remainder of the bonding wire is separated from the second bond portion.