Die Pad Cavity Geometry for Wire Bond Reliability Under Thermal Stress
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Integrated circuit packages face the risk of die pad delamination due to coefficient of thermal expansion (CTE) mismatch between the die pad and mold compound during the curing process, leading to thermal stresses that can disconnect wire bonds and cause open circuits.
Innovation Solution
Incorporating a cavity in the die pad increases the contact area with the mold compound, reducing delamination forces by distributing thermal stresses and providing a stress relief mechanism, thereby preventing delamination and maintaining the wire bond connection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a cavity is added to the die pad to increase contact area with mold compound, then delamination resistance is improved, but device complexity and manufacturing difficulty increase
Solution Approach 1:
The cavity extends the bonding interface from a two-dimensional surface to a three-dimensional structure by creating a recess that penetrates into the die pad. This allows the mold compound to bond to both the top surface and the vertical sidewalls of the cavity, effectively increasing the contact area without increasing the planar footprint of the die pad.
Solution Approach 2:
The cavity divides the bonding interface into multiple segments: the top surface of the die pad and the vertical sidewalls of the cavity. This segmentation creates additional bonding zones that distribute the delamination forces across different areas, improving overall reliability without requiring a single large bonding area.
2Reliability
If a cavity is etched in the die pad to distribute thermal stresses, then delamination force is reduced, but manufacturing precision requirements increase
Solution Approach 1:
The cavity creates a localized region with different mechanical properties compared to the surrounding die pad material. The recessed area provides a controlled zone for stress distribution, while the rest of the die pad maintains its original structural integrity and bonding characteristics.
3Reliability
If the cavity depth is increased to provide more stress relief, then delamination resistance improves, but wire bond attachment difficulty increases
Solution Approach 1:
The cavity is designed to extend partially through the die pad thickness, providing sufficient stress relief and bonding area increase without completely penetrating the die pad. This partial action achieves the necessary stress distribution and bonding enhancement while maintaining a practical depth that allows wire bonds to be attached without excessive difficulty.
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 cavity configuration effectively reduces delamination forces, ensuring a strong bond between the die pad and mold compound, preventing open circuits and allowing for smaller IC package designs without the need for additional space or design changes.
Implementation Method 1
The cause of this phenomena is a coefficient of thermal expansion (CTE) mismatch between the die pad and a mold compound during the curing process. The CTE mismatch creates high thermal stresses between the die pad and the mold compound.
Data Source
AI summary
An integrated circuit and method of making an integrated circuit is provided. The integrated circuit includes an electrically conductive pad having a generally planar top surface that includes a cavity having a bottom surface and sidewalls extending from the bottom surface of the cavity to the top surface of the pad. An electronic device is attached to the top surface of the electrically conductive pad. A wire bond is attached from the electronic device to the bottom surface of the cavity. A molding compound encapsulates the electronic device.