Pre-Molded Leadframe Isolation for Dummy Pad Discharge Risk
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Solution Overview
Problem
In semiconductor devices, the electrical coupling between dummy pads and die pads via tie bars poses a risk of electrical discharge, especially in high-voltage applications, leading to potential device failure due to the short distance between dummy pads and leads in densely packed devices.
Innovation Solution
The electrical coupling between dummy pads and die pads is removed by partially removing the tie bars, creating a recessed portion in the pre-molded leadframe that is filled with molding compound, effectively decoupling the dummy pads from the die pads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dummy pads are provided at tie bars to increase solder joint reliability, then the reliability of solder joints is improved, but electrical discharge risk increases due to electrical coupling between dummy pads and die pads
Solution Approach 1:
The tie bar is segmented into two parts: an first part electrically coupled to the die pad and a second part electrically coupled to the dummy pad. This segmentation breaks the electrical continuity between the dummy pad and die pad while maintaining mechanical support function, thus preventing electrical discharge from affecting the die pad.
Solution Approach 2:
The first part of the tie bar acts as an intermediary element between the die pad and the second part. It provides mechanical support through the dummy pad while being electrically isolated from it, serving as a mediator that separates the mechanical support function from the electrical coupling function.
2Productivity
If the distance between dummy pad and lead is reduced due to high number of leads and reduced device dimensions, then device integration density is improved, but electrical discharge risk increases
Solution Approach 1:
By segmenting the tie bar into electrically isolated parts, the invention enables closer placement of dummy pads to leads without increasing electrical discharge risk to the die pad. The electrical isolation ensures that even if discharge occurs, it is confined to the isolated second part and does not affect the die pad.
3Object-affected harmful factors
If tie bars are partially removed to decouple dummy pads from die pads, then electrical discharge risk is reduced, but manufacturing complexity increases due to additional processing steps
Solution Approach 1:
The tie bar is designed with a preliminary structure that includes the segmentation into first and second parts. This preliminary design allows the electrical isolation to be achieved through standard manufacturing processes without requiring complex post-processing steps, thus reducing manufacturing complexity.
Data Source
AI summary
Electrically insulating material is molded onto a sculptured, electrically conductive leadframe structure that includes a pattern of electrically conductive formations such as a die mounting location configured to have at least one semiconductor die arranged thereon, a dummy pad and a tie bar extending between the die mounting location and the dummy pad. A pre-molded leadframe structure results from the electrically insulating material penetrating into spaces between electrically conductive formations in the pattern of electrically conductive formations. At least one portion of the tie bar extending between the die mounting location and the dummy pad is removed to electrically decouple the dummy pad from the die mounting location.