Lead Frame Nickel Coating Adhesion and Productivity
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Solution Overview
Problem
The existing methods for manufacturing semiconductor packages with single-sided encapsulation, such as SON and QFN packages, face issues with insufficient adhesion between the lead frame and the resin, leading to detachment during the cutting process, and result in low productivity due to complex plating processes and additional equipment requirements.
Innovation Solution
A lead frame with a base material having thick and thin Ni layers on the front and back surfaces, respectively, where the thin section is etched on the front surface to improve adhesion without affecting the back surface, and a Pd and Au layer are applied over both sections, enhancing the anchor effect for resin adhesion without reducing productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a three-layered plating film with a rough surface is formed on the lower surface of the lead frame to improve adhesion between the lead frame and resin, then adhesion strength is improved, but the plating process becomes complex requiring two kinds of Ni-plating solutions and additional equipment
Solution Approach 1:
The patent applies different surface treatments to different areas of the lead frame. Specifically, the lower surface (back surface) is treated to have a rough surface structure to enhance resin adhesion, while the front surface maintains a smooth surface for proper electrical connection and wire bonding. This local differentiation resolves the contradiction by providing enhanced adhesion only where needed (lower surface) without complicating the overall plating process.
Solution Approach 2:
The plating process is segmented into distinct stages: first forming a base Ni layer on the entire lead frame, then selectively forming a rough surface structure only on the lower surface through controlled oxidation or etching. This segmentation allows the complex adhesion-enhancing treatment to be applied only where necessary, avoiding the need for two complete plating lines while achieving the adhesion improvement.
2Reliability
If a rough surface Ni layer is formed on the upper surface of the lead frame to improve resin adhesion, then adhesion strength increases, but wire bonding becomes difficult due to the rough surface
Solution Approach 1:
The patent implements local quality by creating a rough surface structure exclusively on the lower surface of the lead frame where resin adhesion is critical, while maintaining a smooth surface on the front surface where wire bonding occurs. This spatial differentiation ensures that the rough surface enhances adhesion without interfering with the wire bonding process, as the bonding wires contact only the smooth front surface areas.
3Reliability
If two kinds of Ni-plating solutions are used to form Ni layers with different compositions on upper and lower surfaces, then adhesion is improved, but production time increases and productivity decreases
Solution Approach 1:
The plating process is segmented into a first stage where a base Ni layer is formed on the entire lead frame using standard plating, and a second stage where a rough surface structure is selectively formed only on the lower surface through controlled oxidation or etching. This segmentation eliminates the need for two complete plating lines, reducing production time while achieving the adhesion improvement through the rough surface structure on the lower surface only.
Solution Approach 2:
The patent changes the surface parameters (roughness, oxidation state) of the Ni layer selectively on the lower surface after the base plating is complete. By controlling oxidation conditions or etching parameters locally on the lower surface, the rough surface structure is created without requiring a second complete plating process, thus maintaining high productivity while achieving enhanced adhesion.
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 provides improved adhesion between the lead frame and the resin, reducing detachment issues and maintaining productivity by simplifying the plating process, while ensuring no resin leakage or solder wettability deterioration.
Implementation Method 1
a method of manufacturing a lead frame includes a step of forming an Ni layer having a predetermined thickness on a front surface of a metallic base material for mounting of a semiconductor device and on a back surface of the metallic base material for connection with an external board, and a step of etching only the Ni layer formed on the front surface of the metallic base material
Implementation Method 2
a Pd layer and an Au layer are applied over both sections
Data Source
AI summary
A lead frame includes a base material having a front surface for mounting of a semiconductor chip and a back surface for connection with an external board, and an Ni layer having a thick section and thin section. The thick section is formed on the back surface of the base material, whereas the thin section is formed on all or a part of the front surface of the base material. It is preferable that the thick section has a thickness ranging from 2.5 to 5 μm, and the thin section is 0.5-2 μm thinner than the thick section. The lead frame can be manufactured with improved productivity by forming an Ni layer on both front and back surfaces of the base material, and then etching only the Ni layer formed on the front surface of the base material.