QFN Packaging Structure with Multi-Layer Plating for High-Density Leads
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional quad flat no-lead (QFN) packaging structures face issues such as increased manufacturing costs, limited product choices due to high-temperature film requirements, unstable wire bonding, mold bleeding, warpage due to thermal expansion, and difficulties in achieving high-density inner leads.
Innovation Solution
A QFN packaging structure and manufacturing method involving a metal substrate with a multi-layer electrical plating process to reduce lead pitch, wire bonding, and encapsulation with a molding compound, eliminating the need for high-temperature films and minimizing warpage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a high-temperature resistant film is affixed on the back surface of the metal substrate, then the die attaching process can be performed, but the manufacturing cost is directly increased
Solution Approach 1:
The patent removes the high-temperature resistant film from the packaging structure, eliminating the need for this expensive component while still enabling the die attaching process through alternative means
Solution Approach 2:
The patent changes the temperature parameter requirements by using a metal substrate with sufficient thermal stability that can withstand the die attaching process without requiring an additional high-temperature resistant film layer
2Ease of manufacture
If a high-temperature resistant film is affixed on the back surface of the metal substrate, then the die attaching process can be performed, but only epoxy is used in the die attaching process, greatly limiting choices of available products
Solution Approach 1:
By removing the high-temperature resistant film constraint, the patent enables the use of multiple die attaching techniques including eutectic process and soft solder technique, greatly expanding product choices
Solution Approach 2:
The metal substrate is designed to support multiple die attaching methods (epoxy, eutectic, soft solder), making the packaging structure universally applicable to different product requirements and manufacturing preferences
3Device complexity
If a high-temperature resistant film is affixed on the back surface of the metal substrate, then the packaging structure is formed, but the wire bonding parameters become unstable, seriously impacting on the quality of wire bonding and the reliability and stability of the product
Solution Approach 1:
The patent removes the high-temperature resistant film that was causing wire bonding parameter instability, thereby improving wire bonding quality and product reliability
Solution Approach 2:
The patent improves wire bonding stability by changing the thermal and mechanical parameters of the packaging structure through the use of a metal substrate without the soft film layer, providing more stable bonding parameters
4Device complexity
If a high-temperature resistant film is affixed on the back surface of the metal substrate, then the packaging structure is formed, but the molding pressure during the molding process causes certain mold bleeding between the lead frame and the high-temperature resistant film, changing a conductive metal lead into an insulated lead
Solution Approach 1:
The patent removes the high-temperature resistant film that was causing mold bleeding, thereby preventing the insulation of metal leads and maintaining their conductive properties
Solution Approach 2:
The patent changes the material composition parameter by eliminating the soft film layer, making the packaging structure resistant to mold bleeding under pressure and maintaining lead conductivity
5Ease of manufacture
If chemical etching and electrical plating are performed on the metal substrate, then the lead frame carrier is formed, but an expensive high-temperature film must be affixed on the back surface of the metal substrate
Solution Approach 1:
The patent removes the expensive high-temperature film requirement from the lead frame carrier formation process, reducing manufacturing costs while maintaining the functionality achieved through chemical etching and electrical plating
6Ease of manufacture
If chemical half etching is first performed on the back surface of the metal substrate, then the lead frame is formed, but the etching process was carried out twice, manufacturing cost is increased
Solution Approach 1:
The patent combines the etching processes into a single step, merging the back surface etching and inner leads etching into one chemical etching operation, thereby reducing manufacturing cost while still forming the complete lead frame structure
Solution Approach 2:
The single chemical etching process is designed to perform multiple functions simultaneously: creating the back surface pattern and forming the inner leads structure, eliminating the need for separate etching steps
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 wire bonding stability, prevents mold bleeding, and allows for higher density inner leads, improving the reliability and accuracy of the packaging process.
Implementation Method 1
The first metal layer containing a plurality of inner leads corresponding to the plurality of I/O pads and extending to proximity of the die is formed on the metal substrate by a multi-layer electrical plating process
Implementation Method 2
The die, the plurality of inner leads, and metal wires are sealed with a molding compound
Implementation Method 3
metal wires connecting die and the plurality of inner leads
Data Source
AI summary
A quad flat no-lead (QFN) packaging structure. The QFN packaging structure includes a metal substrate, a first outer die pad formed on the metal substrate, and a first die coupled to a top surface of the first outer die pad. The QFN packaging structure also includes a plurality of I/O pads formed on the metal substrate, and a first metal layer containing a plurality of inner leads corresponding to the plurality of I/O pads and extending to proximity of the die. The first metal layer is formed on the metal substrate by a multi-layer electrical plating process such that a lead pitch of the plurality of inner leads is significantly reduced. Further, the QFN packaging structure includes metal wires connecting die and the plurality of inner leads, and a second metal layer formed on a back surface of the plurality of I/O pads and the die pad.