Lead Frame Palladium Plating for Low-Cost Wire Bonding Reliability
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Solution Overview
Problem
Conventional lead frames with a pre-plated frame (PPF) structure require high gold content and thickness for reliable wire bonding, leading to increased manufacturing costs, with gold or gold-silver alloy plating accounting for 50% or more of the total cost.
Innovation Solution
A lead frame with a base substrate having a die pad and lead portions, featuring a nickel plating layer and a palladium plating layer with a thickness of 2 nm to 20 nm, where the palladium layer prevents nickel and copper diffusion after heat treatment, reducing the need for high gold content plating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a gold or gold-silver alloy plating layer with high content and high thickness is applied to prevent diffusion and secure wire bonding reliability, then reliability is improved, but manufacturing cost increases significantly
Solution Approach 1:
The plating structure is divided into multiple functional layers: a base metal layer (copper or copper alloy), a nickel plating layer, and a palladium plating layer. Each layer performs a specific function - the nickel layer provides diffusion barrier and structural support, while the thin palladium layer (2-20 nm) provides oxidation resistance and wire bonding reliability. This segmentation allows each layer to be optimized independently, reducing the need for thick expensive gold plating.
Solution Approach 2:
The nickel plating layer acts as an intermediary between the base metal and the palladium plating layer. It provides a robust diffusion barrier and structural foundation that supports the thin palladium layer, enabling the palladium layer to be much thinner than it would need to be if directly applied to the base metal. This intermediary layer is key to reducing palladium consumption while maintaining reliability.
2Object-generated harmful factors
If a thick palladium plating layer is applied to prevent nickel and copper diffusion, then diffusion prevention is improved, but manufacturing cost increases
Solution Approach 1:
The nickel plating layer is applied first as a preliminary diffusion barrier before applying the palladium layer. This preliminary action of the nickel layer prevents the bulk of nickel and copper diffusion, allowing the subsequent palladium layer to be much thinner (2-20 nm) while still providing adequate diffusion prevention. The nickel layer does the heavy lifting of diffusion blocking, enabling cost reduction in the palladium layer.
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 proposed lead frame design reduces manufacturing costs while maintaining high reliability by minimizing the use of expensive gold or gold-silver alloys, achieving this through the use of a thin, high-density palladium plating layer.
Implementation Method 1
a palladium plating layer arranged on the nickel plating layer, including palladium, and having a thickness of 2 nm to 20 nm, wherein the palladium plating layer satisfies the following condition (1): After heating the lead frame at 340° C. for 1 minute, the amount of nickel (Ni) detected on the surface of the lead frame by X-ray photoelectron spectroscopy (XPS) analysis is 1.0 at % or less
Implementation Method 2
the palladium plating layer is formed by an electroplating method of applying a current having an on-off square wave having an on-current period shorter than an off-current period
Data Source
AI summary
According to one or more embodiments, a method of manufacturing a lead frame, includes processing a base metal into a base substrate having a die pad portion and a lead portion, forming a nickel plating layer on the base substrate, and forming a palladium plating layer on the base substrate, wherein the palladium plating layer is formed by an electroplating method of applying a current having an on-off square wave having an on-current period shorter than an off-current period.