Laser Ablation of OSP Layer for Wire Bonding on PCB
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Solution Overview
Problem
Current surface finishes like ENIG and ENEPIG for printed circuit boards are expensive and prone to failures in wire bonding processes, necessitating a cost-effective alternative that minimizes connection failures.
Innovation Solution
A printed circuit board with an organic solderability preservative (OSP) layer treated by laser ablation, providing a wirebondable surface using a water-based azole compound that protects copper and allows for connections with aluminum, copper, silver, or gold bondwires.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ENIG or ENEPIG surface finish is used for wire bonding, then connection reliability is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive ENIG/ENEPIG surface finishes with a cheaper OSP (organic solderability preservative) coating that is applied as a thin organic layer. This disposable-like approach uses a cost-effective alternative material that achieves the necessary wire bonding reliability without the high cost of nickel-gold or nickel-palladium-gold multi-layer finishes
Solution Approach 2:
The patent changes the fundamental parameter of surface finish material from metallic (ENIG/ENEPIG) to organic (OSP), and further modifies it by applying laser ablation to create specific surface characteristics. This parameter change enables wire bonding on a previously unsuitable material, achieving both cost reduction and reliability
2Reliability
If ENIG surface finish is used, then wire bonding reliability is improved, but phosphorus buildup causes surface fracture and connection failure
Solution Approach 1:
The patent eliminates the phosphorus-containing nickel layer entirely by using OSP (organic solderability preservative) instead of ENIG. This replacement removes the source of phosphorus buildup that causes intermetallic compound formation and surface fracture, while still providing a wire-bondable surface through laser ablation treatment
Solution Approach 2:
The patent extracts and removes the problematic nickel-phosphorus intermediate layer from the surface finish structure. By using OSP directly on copper and applying laser ablation, the process eliminates the nickel layer that generates phosphorus buildup, thereby preventing connection failures
3Ease of manufacture
If OSP layer is used without laser treatment, then manufacturing cost is reduced, but wire bonding capability is insufficient
Solution Approach 1:
The patent applies laser ablation as a preliminary treatment to the OSP-coated copper surface before wire bonding. This preliminary action modifies the OSP layer to create a surface with appropriate characteristics for wire bonding, enabling the cost-effective OSP material to achieve the necessary bonding capability
Solution Approach 2:
The patent replaces traditional mechanical or chemical surface preparation methods with laser ablation. The laser provides a non-contact, precise method to modify the OSP surface, creating wire-bondable characteristics without the complexity of mechanical polishing or chemical etching processes
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 OSP layer offers a cost-effective solution with improved reliability and reworkability, reducing the overall cost of PCBs while maintaining effective solder and press-fit connections.
Implementation Method 1
exposing a surface of the copper layer by applying a laser beam from a laser on the OSP layer
Data Source
AI summary
A printed circuit board is disclosed. The printed circuit board includes: a substrate layer; a copper layer disposed on the substrate layer; and an organic solderability preservative (OSP) layer disposed on the copper layer. The OSP layer defines one or more laser treated OSP surfaces.