OSP-Coated Copper Wire Bonding for Semiconductor Packages
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Solution Overview
Problem
Gold wire bonding in semiconductor packages faces issues such as high electrical resistance, heat generation, low tensile strength, and poor bonding reliability due to inter-diffusion with aluminum, and the use of copper wire is hindered by oxidation of bond pads, leading to unreliable connections.
Innovation Solution
The use of Organic Solderability Preservative (OSP) coated copper wire bonding between copper, aluminum, or silver bond pads and lead fingers, eliminating the need for nickel and gold coatings and improving bonding reliability through the Stand Off Stitch on ball Bonding (SSB) process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper wire is used for bonding, then electrical conductivity and heat dissipation are improved, but oxidation of bond pad surface occurs leading to poor bonding reliability
Solution Approach 1:
An Organic Solderability Preservative (OSP) coating is applied as an intermediary layer on the copper bond pad surface. This OSP layer acts as a mediator that prevents direct oxidation of the copper while maintaining bonding compatibility with the copper wire, thereby resolving the contradiction between using copper for its conductivity and preventing its oxidation.
Solution Approach 2:
The bonding process is performed in a forming gas atmosphere (typically nitrogen-hydrogen mixture) that creates an inert environment preventing copper oxidation. This inert atmospheric condition allows the copper bond pad and copper wire to maintain their metallic surfaces without oxidizing during the bonding operation.
2Ease of manufacture
If gold wire is used for bonding, then bonding process is simplified, but electrical resistance increases and heat generation occurs due to inter-diffusion with aluminum
Solution Approach 1:
The invention changes the wire material parameter from gold to copper, and相应地 changes the bond pad material to copper (with OSP coating). This parameter change exploits copper's superior electrical conductivity and lower inter-diffusion tendency with aluminum, thereby improving electrical connection quality while maintaining manufacturing feasibility through the OSP protection system.
3Strength
If copper wire is used for bonding, then tensile strength and wire stability are improved, but oxidation prevents effective wire-to-pad bonding
Solution Approach 1:
The OSP coating serves as an intermediary protective layer on the copper bond pad that prevents oxide formation while remaining compatible with copper wire bonding. This intermediary layer allows the high-strength copper wire to bond effectively to the copper pad without the bonding interface being degraded by oxidation.
Data Source
AI summary
A semiconductor package and a method for constructing the package are disclosed. The package includes a substrate and a die attached thereto. A first contact region is disposed on the substrate and a second contact region is disposed on the die. The first contact region, for example, comprises copper coated with an OSP material. A copper wire bond electrically couples the first and second contact regions. Wire bonding includes forming a ball bump on the first contact region having a flat top surface. Providing the flat top surface is achieved with a smoothing process. A ball bond is formed on the second contact region, followed by stitching the wire onto the flat top surface of the ball bump on the first contact region.