Lead Frame Corner Exposure for Sacrificial Oxide Delamination Control
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Solution Overview
Problem
Existing lead frames for semiconductor devices face issues with delamination due to coefficient of thermal expansion mismatches between packaging regions and the lead frame, leading to mechanical stresses and reliability concerns, particularly at the corners of the die pad, which existing solutions like adhesion promoters, holding structures, and rough lead frames either fail to address effectively or incur high costs.
Innovation Solution
A lead frame design where the corners of the die pad are left exposed to form sacrificial oxidized regions during the manufacturing process, which reduces delamination by enhancing adhesion between the packaging region and the top coating structure, preventing propagation of delamination and maintaining device reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the die pad is completely coated with top coating structure, then oxidation resistance is improved, but delamination occurs due to thermal expansion mismatch
Solution Approach 1:
The top coating structure is applied selectively to specific regions of the die pad rather than uniformly across the entire surface. The coating covers the central region and edges while leaving corner portions exposed, creating local variations in coating presence. This local quality approach allows the coated areas to provide oxidation resistance while the exposed corners serve as sacrificial zones that absorb thermal stress, preventing delamination of the coated regions.
2Strength
If adhesion promoters are used to prevent delamination, then adhesion strength is improved, but manufacturing cost increases
Solution Approach 1:
The invention converts the harmful effect of thermal expansion mismatch into a beneficial outcome by intentionally exposing corner portions of the die pad. These exposed corners act as sacrificial elements that undergo oxidation and absorb mechanical stress, thereby protecting the coated regions from delamination. This approach eliminates the need for expensive adhesion promoters while actually improving adhesion strength through the stress-absorbing mechanism of the exposed corners.
3Strength
If holding structures are added to prevent delamination, then adhesion strength is improved, but device complexity increases
Solution Approach 1:
The invention extracts or removes material from the corner portions of the die pad, leaving these areas exposed and free of top coating structure. This extraction creates sacrificial zones that inherently prevent delamination through stress absorption, eliminating the need for additional holding structures. The solution simplifies the overall device structure by using a geometric modification rather than adding complex mechanical holding features.
4Strength
If rough lead frame is used to enhance adhesion, then adhesion strength is improved, but manufacturing precision is reduced
Solution Approach 1:
The invention applies the top coating structure to specific regions of the die pad before final assembly, leaving corner portions exposed. This preliminary action of selective coating creates a structured pattern that inherently prevents delamination through stress distribution. The method maintains manufacturing precision by using controlled coating processes that precisely define coated and exposed regions, avoiding the need for roughening operations that would compromise surface precision.
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 design effectively reduces delamination between the packaging region and the metallic coating regions, ensuring the die remains encapsulated without exposure to the external atmosphere, thereby enhancing the reliability and cost-effectiveness of the semiconductor device packaging.
Implementation Method 1
the top coating structure leaves exposed a number of corner portions of the top structure surface
Implementation Method 2
delamination due to coefficient of thermal expansion mismatches between packaging regions and the lead frame
Data Source
AI summary
A lead frame for an integrated electronic device includes a die pad made of a first metallic material. A top coating layer formed by a second metallic material is arranged on a top surface of the die pad. The second metallic material has an oxidation rate lower than the first metallic material. The top coating layer leaves exposed a number of corner portions of the top surface of the die pad. A subsequent heating operation, for example occurring in connection with wirebonding, causes an oxidized layer to form on the corner portions of the top surface of the die pad at a position in contact with the top coating layer.