Leadframe Lead Lock Structure for CTE-Driven Delamination
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Solution Overview
Problem
Integrated circuit (IC) packages face the risk of open circuits due to wire bond disconnection and leadframe lead delamination caused by coefficient of thermal expansion (CTE) mismatch between leads and the mold compound during the curing process.
Innovation Solution
The implementation of a fence type lead lock configuration with partially etched side supports and defined openings adjacent to the side supports, which increases the contact area with the mold compound, thereby resisting delamination forces and reducing thermal stresses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional leadframe structure is used without lead locks, then the device complexity is low, but the reliability deteriorates due to delamination and wire bond disconnection during curing
Solution Approach 1:
The lead lock is divided into multiple side supports (e.g., first side support, second side support) that are positioned at different locations along the inner lead. This segmentation allows the lead lock to resist delamination forces at multiple points, improving reliability without requiring a single complex structure
Solution Approach 2:
The lead lock extends in the vertical dimension above the leadframe, creating a three-dimensional structure that provides mechanical restraint against delamination. This vertical extension adds a new dimensional approach to solving the delamination problem without complicating the planar leadframe layout
2Strength
If the contact area between mold compound and leads is increased to resist delamination, then the adhesion strength improves, but the device complexity increases due to additional structural elements
Solution Approach 1:
The lead lock structure is pre-formed as an integral part of the leadframe before the molding process. This preliminary action ensures that the adhesion-enhancing structure is already in place to resist delamination forces during curing, eliminating the need for additional post-processing steps or complex assembly operations
Solution Approach 2:
The lead lock is merged with the leadframe as a single integrated structure, where the side supports are continuous with the inner leads. This merging eliminates the need for separate adhesive layers or additional components, achieving enhanced adhesion strength without proportionally increasing device complexity
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 enhances the adhesion strength of the mold compound, reducing the delamination force and preventing wire bond disconnection, thus ensuring reliable connections and reducing the risk of open circuits.
Implementation Method 1
a mold compound is formed to encapsulate the plurality of dies, the inner leads, the lead locks, and the wire bonds
Implementation Method 2
This configuration enhances the adhesion strength of the mold compound, reducing the delamination force
Implementation Method 3
The cause of this phenomena is a coefficient of thermal expansion (CTE) mismatch between the leads and a mold compound during the curing process. The CTE mismatch creates high thermal stresses between the leads and the mold compound
Data Source
AI summary
An electronic device includes a leadframe having a die pad, inner leads, and outer leads. The die is attached to the die pad, where the die includes an active side. Lead locks are disposed adjacent to the inner leads. The lead locks include a side support disposed on each side of the inner leads and an opening defined between each side support and the inner leads. Wire bonds are attached from the active side of the die to the inner leads and a mold compound is formed to encapsulate the die, the inner leads, the lead locks, and the wire bonds.