Multilayer Lead Frame Coating for Wire Bonding and Encapsulant Adhesion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional lead frames with silver coatings suffer from high costs and weak mechanical bonding with the encapsulant, while also being time-consuming to apply, and do not provide a sufficient hardware interface for semiconductor packages with minimal electrical signal degradation and environmental protection.
Innovation Solution
A lead frame with a copper alloy base material coated with a multilayer structure consisting of electroplated copper, a precious metal layer, and an adhesion promotion compound, such as silver oxide, to enhance wire bonding and encapsulant adhesion, smoothing surface defects and improving mechanical coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a thick silver coating (3 μm) is applied to the lead frame, then wire bonding quality is improved, but manufacturing cost increases and mechanical bonding with encapsulant weakens
Solution Approach 1:
The patent divides the single thick silver coating into multiple functional layers: a thin silver layer (0.01-0.1 μm) for wire bonding, a copper layer (0.1-2.0 μm) for surface smoothing and conductivity, and a nickel layer (0.1-1.0 μm) for mechanical strength and encapsulant bonding. This segmentation allows each layer to optimize its specific function while reducing overall precious metal usage.
Solution Approach 2:
The patent applies different material properties to different layers: the silver layer provides excellent electrical conductivity and wire bonding characteristics, the copper layer provides surface smoothness and electrical conductivity, and the nickel layer provides mechanical strength and adhesion to the encapsulant. Each layer is locally optimized for its specific function.
2Reliability
If spot coating process is used to apply silver coating, then wire bonding is improved, but manufacturing time increases
Solution Approach 1:
The copper underlayer serves multiple functions: it smooths surface defects from the lead frame, provides electrical conductivity, and acts as a barrier between the silver and copper alloy base material. This multi-functionality eliminates the need for separate surface preparation steps, reducing manufacturing time while maintaining wire bonding quality.
3Strength
If the lead frame base material has high hardness (100-200 HV), then structural strength is improved, but surface scratching during rolling increases
Solution Approach 1:
The copper underlayer is applied in advance to smooth out surface scratches and defects created during the rolling process. This preliminary smoothing action occurs before the final silver coating is applied, ensuring that the wire bonding surface is defect-free while the underlying structure maintains its required 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
The multilayer coating improves the quality of electrical connections, reduces costs, and maintains structural support and environmental protection, while simplifying the coating process and increasing the strength of mechanical bonding between the encapsulant and the lead frame.
Implementation Method 1
a first coating of copper (e.g., electroplated copper)
Implementation Method 2
The third coating is an adhesion promoter to increase the strength of a mechanical coupling of the encapsulant to the lead frame
Data Source
AI summary
The present disclosure is directed to a lead frame design that includes a copper alloy base material coated with an electroplated copper layer, a precious metal, and an adhesion promotion compound. The layers compensate for scratches or surface irregularities in the base material while promoting adhesion from the lead frame to the conductive connectors, and to the encapsulant by coupling them to different layers of a multilayer coating on the lead frame. The first layer of the multilayer coating is a soft electroplated copper to smooth the surface of the base material. The second layer of the multilayer coating is a thin precious metal to facilitate a mechanical coupling between leads of the lead frame and conductive connectors. The third layer of the multilayer coating is the adhesion promotion compound for facilitating a mechanical coupling to an encapsulant around the lead frame.