Barrel-Plated QFN Packaging Reducing Warpage and Lead Pitch
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Solution Overview
Problem
Conventional quad flat no-lead (QFN) packaging technologies face issues such as increased manufacturing costs, limited product choices due to high-temperature film requirements, unstable wire bonding, mold bleeding, and warpage of lead frames, which affect the accuracy and yield of die attaching and wire bonding processes.
Innovation Solution
A method involving a metal substrate with a first photoresist film and multi-layer electrical plating to form inner leads with reduced lead pitch, followed by die attaching, wire bonding, and barrel plating to form I/O pads, reducing lead frame warpage and increasing lead density, while eliminating the need for separate etching processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If chemical etching and electrical plating are performed on the metal substrate followed by affixing a high-temperature resistant film, then the lead frame can withstand high-temperature processes, but the manufacturing cost increases due to the expensive film material
Solution Approach 1:
The patent extracts and removes the high-temperature resistant film from the lead frame structure, replacing it with a metal substrate that inherently withstands high temperatures. This eliminates the need for the expensive film while maintaining temperature resistance through the metal substrate's own properties and the barrel-plating process.
Solution Approach 2:
The patent changes the fundamental parameter of temperature resistance from being provided by an organic film coating to being provided by the metal substrate itself and its metallization layers. The barrel-plating process creates a robust metal surface that can directly withstand high-temperature die attaching processes without requiring additional protective films.
2Temperature
If a high-temperature resistant film is affixed on the back surface of the metal substrate, then the lead frame can survive die attaching, but the wire bonding parameters become unstable impacting quality and reliability
Solution Approach 1:
The patent removes the high-temperature resistant film that was causing wire bonding instability. By eliminating this soft material layer, the wire bonding process operates directly on the metal substrate surface, providing stable parameters and consistent bonding quality throughout the manufacturing process.
3Temperature
If a high-temperature resistant film is affixed on the metal substrate, then the lead frame can withstand die attaching, but mold bleeding occurs between the lead frame and film during molding
Solution Approach 1:
The patent extracts and eliminates the high-temperature resistant film that was causing mold bleeding. By removing this soft material layer, the molding compound has a solid metal surface to bond to, preventing bleeding and maintaining lead conductivity throughout the molding process.
4Ease of manufacture
If the inner leads are formed using etching technique, then the lead frame structure is created, but the lead pitch cannot be significantly reduced limiting high density achievement
Solution Approach 1:
The patent inverts the conventional sequence by first forming metal layers through barrel-plating, then etching through these pre-formed layers to create the lead frame structure. This allows for much finer lead pitch because the etching process works on already-deposited metal layers that can be patterned at higher densities, rather than trying to etch fine features directly into the substrate.
Solution Approach 2:
The patent performs preliminary barrel-plating to deposit metal layers before etching. This preliminary metallization allows subsequent etching to create precise, high-density lead patterns with reduced pitch, as the metal layers provide a stable foundation for fine-feature etching that would be difficult to achieve directly on the substrate.
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 reduces manufacturing costs, enhances lead density, stabilizes wire bonding, and prevents mold bleeding, improving the accuracy and yield of the packaging process by eliminating warpage and allowing high-temperature tolerance of the lead frame.
Implementation Method 1
forming a first metal layer containing a plurality of inner leads for each of the plurality of QFN components by a multi-layer electrical plating process
Implementation Method 2
forming a second metal layer on a back surface of I/O pads in the individual QFN components by a barrel plating process
Data Source
AI summary
A barrel-plating quad flat no-lead (QFN) package structure and a method for manufacturing the same. The method includes: providing a metal substrate for a plurality of QFN components; forming a first photoresist film on a top surface of the substrate; forming a plating pattern in the first photoresist film; forming a first metal layer containing a plurality of inner leads; etching the substrate from the back surface of the substrate to form a plurality of I/O pads; filling sealant in the etched areas; attaching at least one die in a predetermined region on the top surface of the substrate; connecting the die and the inner leads using metal wires; sealing the die, the inner leads, and the metal wires with a molding compound; separating the resulting joint QFN components into individual QFN components; and forming a second metal layer on the back surface of the I/O pads.