Lead Frame Overhang Formation via Nitrogen-Modified Etching
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Solution Overview
Problem
Existing lead frame manufacturing methods face challenges in preventing defects such as burrs and chipping, and ensuring the sealing resin does not come off during resin sealing, especially when forming overhangs with conventional etching techniques.
Innovation Solution
A lead frame with concavities forming columnar portions where the horizontally deepest portion is positioned lower than the vertical center, using an etching solution containing an organic compound with nitrogen affinity to copper as an inhibitor, which inhibits etching in horizontal directions, preventing through holes and enhancing overhang formation with reduced vertical etching, thus minimizing defects and improving resin adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If conventional etching techniques are used to form overhangs, then overhang formation is achieved, but defects such as burrs and chipping occur and resin may come off during sealing
Solution Approach 1:
The patent changes the chemical parameters of the etching solution by adding an organic compound containing nitrogen that has affinity to copper. This chemical parameter change modifies the etching behavior to preferentially etch in the vertical direction while suppressing horizontal etching, thereby forming overhangs with reduced defects such as burrs and chipping, and improving resin adhesion during sealing.
Solution Approach 2:
The patent creates local quality differences in the etching process by using the nitrogen-containing organic compound that selectively interacts with copper surfaces. This creates different etching rates in different spatial locations and directions, allowing overhangs to form with proper morphology that prevents resin detachment while minimizing surface defects.
2Length of stationary object
If the horizontally deepest portion of the concavity is positioned at or above the vertical center, then etching depth is sufficient, but overhang thickness is reduced and defects increase
Solution Approach 1:
By changing the chemical composition of the etching solution to include nitrogen-containing organic compounds with copper affinity, the patent achieves preferential vertical etching. This allows the horizontally deepest portion to be positioned lower than the vertical center while maintaining sufficient overall etching depth, thereby forming thicker overhangs with fewer defects.
Solution Approach 2:
The patent creates asymmetric etching behavior where vertical etching is promoted and horizontal etching is suppressed through the use of nitrogen-containing organic compounds. This asymmetric etching pattern naturally forms overhangs with the horizontally deepest portion positioned lower than the vertical center, achieving both sufficient depth and proper overhang morphology.
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 solution effectively reduces defects like burrs and chipping, enhances the capability of columnar portions to prevent resin from coming off, and maintains design freedom by forming overhangs with large thickness, ensuring reliable resin sealing without sacrificing wiring design flexibility.
Implementation Method 1
performing half-etching treatment from the front-surface side of the copper plate using an etching solution containing, as an etching inhibitor, an organic compound containing nitrogen having affinity to copper
Implementation Method 2
to form a concavity defining columnar portions that are to serve as internal connecting terminals, respectively, or internal connecting terminals and pads, respectively, by dissolving and removing the copper plate
Implementation Method 3
using an etching solution containing, as an etching inhibitor, an organic compound containing nitrogen having affinity to copper, which inhibits etching in horizontal directions
Data Source
AI summary
A lead frame has a concavity formed on the upper-surface side of a metal plate and columnar portions defined by the concavity. A horizontally deepest portion regarding a side face shape of the concavity is positioned lower than the vertical center position of the concavity. Thereby, overhangs projecting from the top faces of the columnar portions rarely cause shape defects or burr defects and thus the lead frame has an enhanced capability, by the columnar portions, of preventing a sealing resin from coming off without sacrificing the freedom of wiring design.