Leadframe Free-End Plating to Reduce Overmolding Lead Flash
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Solution Overview
Problem
Existing semiconductor package manufacturing processes face challenges with lead flash formation during overmolding, which can lead to solderability issues and reduced reliability of connections between leads and printed circuit boards, especially with short leads lacking bends.
Innovation Solution
The use of a lead frame with a dam-bar having reduced thickness portions that act as barriers during overmolding, exposing specific surfaces of the leads for plating and minimizing lead flash formation, followed by plating with conductive material to enhance solderability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If leads are overmolded with insulating material during package manufacturing, then the insulating material provides electrical insulation and structural support, but lead flash formation occurs on the lead surfaces
Solution Approach 1:
The lead frame is pre-plated with conductive material before overmolding. This preliminary plating action ensures that when insulating material later contacts the leads during overmolding, the lead flash that forms occurs on the plating surface rather than on the base lead material, making it more easily removed and less harmful to subsequent soldering processes
Solution Approach 2:
The invention converts the harmful lead flash formation during overmolding into a beneficial process by having the flash form on a pre-applied plating layer. The flash that would normally contaminate the lead surface is instead allowed to form on the plating material, which can then be controlled and removed more effectively, actually improving the cleanliness of the final lead surface for soldering
2Productivity
If lead flash is present on lead surfaces after overmolding, then the manufacturing process is simplified, but solderability of the leads deteriorates
Solution Approach 1:
Conductive plating material is applied to the leads before the overmolding process. This preliminary plating creates a controlled surface that manages how lead flash forms during subsequent manufacturing steps, ensuring that any flash that does form can be more easily removed without compromising the underlying lead surface quality for soldering
Solution Approach 2:
The invention changes the surface parameters of the leads by applying a plating layer with specific material properties. This plating layer has different characteristics than the base lead material, allowing it to control flash formation behavior and provide a surface that maintains or improves solderability even after exposure to overmolding processes
3Device complexity
If conventional overmolding processes are used without pre-plating, then manufacturing steps are reduced, but connection reliability between leads and PCB decreases
Solution Approach 1:
The lead frame receives a conductive plating treatment before being assembled and overmolded. This preliminary action of plating the leads ensures that when insulating material contacts the leads during overmolding, the interaction occurs on a controlled plating surface rather than the raw lead surface, preventing contamination and maintaining connection reliability
Solution Approach 2:
The conductive plating material serves as an intermediary layer between the base lead material and the insulating overmold material. This intermediate plating layer manages the interaction between the metal lead and polymer insulator, controlling flash formation and protecting the underlying lead surface to ensure reliable electrical connections
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
This configuration reduces lead flash formation, improves solderability, and increases the reliability of connections between semiconductor package leads and printed circuit boards by ensuring better wettability and inspection of solder connections.
Implementation Method 1
The overmolded lead frame is plated with an electrically conductive material that covers at least portions of the outer surfaces
Data Source
AI summary
A semiconductor package includes a die pad and leads extending from the die pad. Each lead has a free end with outer surfaces extending at angles from one another. An electrically conductive plating material covers at least portions of the outer surfaces. A die attached to the die pad is electrically connected to the leads. An insulating layer extends over the leads and the die such that the free ends of the leads are exposed.