Recessed Die Attach Pad for IC Packaging Stress Relief
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Solution Overview
Problem
Integrated circuit (IC) packaging faces challenges with stress-induced delamination and damage due to thermal expansion and cyclic operational stresses, particularly at the die and die attach pad interfaces, exacerbated by rapid heating and cooling processes and non-uniform adhesive thickness.
Innovation Solution
The design incorporates a leadframe with a recessed die attach pad, where the die edges overhang the recessed regions, allowing for increased adhesive thickness in high-stress areas and facilitating uniform adhesive distribution, along with a method of depositing a thin metallic film using a recessed die attach pad and oversized mechanical mask for precise ring plating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If rapid heating and cooling processes are used during encapsulation, then productivity is improved, but stress-induced delamination and damage occur due to non-uniform thermal expansion
Solution Approach 1:
The die attach pad is designed with a recessed peripheral region that is lower than the central region, creating different local heights. This allows the adhesive layer to have non-uniform thickness, with greater thickness at the high-stress peripheral regions where the die edges overhang, and thinner adhesive in the central region. This local variation in adhesive thickness provides enhanced stress relief at critical locations while maintaining overall structural integrity during rapid thermal cycling.
2Ease of manufacture
If uniform adhesive thickness is used across the die attach pad, then manufacturing simplicity is maintained, but stress concentration occurs at the die edges during thermal cycling
Solution Approach 1:
The recessed peripheral region creates a geometric feature that naturally guides adhesive distribution. The adhesive material accumulates in the recessed area due to the depth difference, automatically achieving greater thickness at the edges without requiring complex application processes. This maintains manufacturing simplicity while achieving the desired non-uniform thickness profile for stress management.
3Manufacturing precision
If the die is fully supported by the die attach pad surface, then manufacturing precision is simplified, but the probability of delamination increases under thermal stress
Solution Approach 1:
The recessed peripheral region is designed in advance to accommodate excess adhesive material, creating a built-in cushioning layer before thermal stress occurs. This pre-positioned thicker adhesive layer acts as a stress-absorbing buffer that prevents delamination during subsequent thermal cycling, without affecting the die positioning process.
4Stress or pressure
If the adhesive layer is made uniformly thick across the entire die attach pad, then stress distribution is improved, but package thickness increases
Solution Approach 1:
The adhesive layer thickness is optimized locally rather than uniformly. The thicker adhesive is concentrated specifically in the recessed peripheral region where stress concentration occurs, while the central region maintains a thinner adhesive profile. This localized approach provides stress relief where needed without unnecessarily increasing the overall package thickness.
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 the probability of delamination and stress-related damage, enabling more robust and reliable IC packages with improved moisture sensitivity performance and reduced package thickness.
Implementation Method 1
non-uniform expansion as a result of the differences in the coefficients of thermal expansion of the die, die attach material, leadframe and molding material leads to high stresses that can result in delamination
Implementation Method 2
A die is adhesively secured to the top surface of the die attach pad
Implementation Method 3
The metal film is then deposited on the recessed region using a conventional deposition technique such as sputtering
Data Source
AI summary
Particular embodiments of the present invention provide a leadframe suitable for use in packaging IC dice that enables stress reduction in and around the die, die attach material, die attach pad and mold interfaces. More particularly, various leadframes are described that include recesses in selected regions of the top surface of the die attach pad.