Selective Gold Removal from Lead Frame for Mold Adhesion
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Solution Overview
Problem
The existing method of integrated circuit packaging faces failures due to imperfect adhesion of the mold compound to the lead frame, leading to moisture ingress and reduced packaging yield, as the gold layer on the lead frame interferes with the adhesion while providing beneficial solder wetting properties.
Innovation Solution
A method involving the substantial removal of the gold layer from the top surface of the lead frame using a plasma process, allowing direct contact between the mold compound and the palladium layer for improved adhesion without compromising solder wetting on the bottom surface, thereby enhancing the reliability of the packaged integrated circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the gold layer is substantially removed from the lead frame, then moisture ingress is reduced through improved adhesion, but manufacturing complexity increases
Solution Approach 1:
The patent extracts the gold layer selectively from specific regions of the lead frame using plasma etching. This extraction process removes only the necessary portions of gold (from the top surface) while leaving other portions intact (bottom surface), achieving improved moisture resistance without requiring complete removal of the gold layer which would complicate manufacturing.
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 approach significantly reduces the failure rate of packaged integrated circuits by improving the adhesion of the mold compound to the lead frame, as demonstrated by increased moisture sensitivity levels and connection strength, while maintaining the beneficial solder wetting properties on the bottom surface.
Implementation Method 1
The outermost gold layer is substantially removed from a portion of the top surface of the lead frame
Data Source
AI summary
A method of packaging an integrated circuit, including providing a lead frame having lead fingers, where the lead frame has a gold layer thereon on a top surface and a bottom surface. An integrated circuit die is attached to the lead frame. The gold layer is substantially removed from portions of the top surface of the lead frame. The integrated circuit die is wire bonded to the lead fingers with a plurality of wire stitches subsequent to substantially removing the gold. The die is encapsulated in a mold compound to form a packaged integrated circuit.