Lead Frame Plating for Copper Wire Bonding Reliability
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Solution Overview
Problem
Copper wires, due to their higher oxidization, hardness, and lower ductility, exhibit poor wire bonding properties compared to gold wires, leading to slipping and bonding failures when used in palladium pre-plated lead frames, which are more expensive and less reliable.
Innovation Solution
A lead frame with a four-layer plating structure on the substrate frame, including a nickel, palladium, silver, and gold plating sequence, applied to the bonding wire connection areas, and a three-layer plating without silver on the exposed outer leads, to enhance bonding reliability and prevent oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If copper wires are used instead of gold wires for wire bonding, then material cost is reduced, but wire bonding property deteriorates due to oxidation, hardness, and lower ductility
Solution Approach 1:
A silver plating layer is introduced as an intermediary between the copper wire and the palladium pre-plated lead frame. This silver layer acts as a mediator that improves bonding properties by providing a more suitable bonding surface, preventing direct contact between the copper wire and the hard palladium surface, thereby resolving the wire bonding property deterioration issue while maintaining the use of cost-effective copper wires
Solution Approach 2:
The lead frame employs a composite plating structure with multiple layers (nickel base layer, palladium intermediate layer, and silver bonding layer). This composite material approach combines the advantages of each layer: nickel provides structural support, palladium prevents oxidation and provides good adhesion, and silver provides excellent wire bonding properties, thereby achieving reliable copper wire bonding without using expensive gold wires
2Reliability
If a four-layer plating (Ni-Pd-Ag-Au) is applied to bonding portions, then wire bonding property is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies different plating structures to different regions of the lead frame: a four-layer plating (Ni-Pd-Ag-Au) is applied to bonding portions where wire bonding is required, while a simpler three-layer plating (Ni-Pd-Pt) is applied to exposed outer leads. This local differentiation optimizes wire bonding property where needed while reducing manufacturing complexity in other areas
Solution Approach 2:
The plating process is segmented into distinct regions with different layer configurations. The bonding portions receive the full four-layer treatment for optimal wire bonding, while non-bonding areas receive a simplified plating structure. This segmentation allows the system to achieve high reliability where necessary without incurring the full manufacturing complexity across the entire component
3Reliability
If a three-layer plating (Ni-Pd-Pt) is applied to outer leads, then solder wettability is maintained, but oxidation resistance is reduced compared to four-layer plating
Solution Approach 1:
The nickel base layer serves as an intermediary that provides oxidation resistance to the outer leads. By positioning the nickel layer at the base of the plating structure, it protects the underlying copper substrate from oxidation while allowing the outer Pd and Pt layers to maintain good solder wettability. This intermediary approach resolves the contradiction between oxidation resistance and solder wettability
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 four-layer plating significantly improves the tensile strength and connection reliability of copper wires by reducing surface hardness and preventing slipping, while the three-layer plating on outer leads avoids issues like land delamination and sulfurization, maintaining solder wettability and reliability.
Implementation Method 1
a nickel plating layer 11A, which serves as a lowermost or substratum layer
Implementation Method 2
a palladium plating layer 12A... the palladium plating layer 12A, and a gold plating layer 14A. The plating layers 11A, 12A and 14A are sequentially laminated on the copper or copper alloy base material 51
Implementation Method 3
the gold plating layer 14A, which is formed as the uppermost layer, prevents oxidization of the lead frame and provides a good wire bonding property for a bonding wire
Implementation Method 4
a nickel plating layer 11A, which serves as a lowermost or substratum layer, a palladium plating layer 12A, and a gold plating layer 14A. The plating layers 11A, 12A and 14A are sequentially laminated on the copper or copper alloy base material 51
Data Source
AI summary
A lead frame for a resin-seal type semiconductor device, which includes a semiconductor element having an electrode, a bonding wire connected to the electrode of the semiconductor element, and a sealing resin covering and sealing the semiconductor element and the bonding wire. The lead frame includes a substrate frame, a four-layer plating, and a three-layer plating. The substrate frame include leads, a connection region, which is sealed by the sealing resin and connected to the bonding wire, and an exposed region, which is not sealed by the sealing resin. A four-layer plating is applied to a portion of the substrate frame that is to be connected to the bonding wire and sealed by the sealing resin. A three-layer plating is applied to an exposed region of the substrate frame that is exposed from the sealing resin.