Two-Sided Bondable Lead Frame for Thermal Dissipation
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Solution Overview
Problem
In the design and manufacturing of lead frames for quad flat no-leads (QFN) and dual flat no-leads (DFN) packages, there is a need for efficient thermal dissipation and connectivity to printed circuit boards (PCBs) without through holes, while accommodating dies of varying sizes, which existing technologies struggle to balance effectively.
Innovation Solution
A lead frame with two bondable pads on either side, where one pad is used for die attachment and the other for thermal dissipation and connectivity to the PCB, with the unused pad being exposed after molding, allowing for flexible thermal management and electrical connections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a single pad is used for die attachment in QFN/DFN packages, then the structure is simple, but thermal dissipation efficiency is insufficient
Solution Approach 1:
The lead frame is designed with two pads on opposite sides, where one pad serves for die attachment and the other pad provides thermal dissipation and electrical connectivity to the PCB. This multi-functional design allows the lead frame to simultaneously achieve mechanical support, thermal management, and electrical connection functions, resolving the contradiction between simple structure and efficient thermal dissipation.
2Adaptability or versatility
If the lead frame is designed for through-hole mounting, then PCB connectivity is established, but the no-leads package requirement cannot be met
Solution Approach 1:
Instead of using traditional through-hole mounting where leads pass through the PCB, this invention inverts the approach by providing surface-mounted pads on the lead frame that directly bond to the PCB surface. The pads extend beyond the molding encapsulation and are positioned for surface-mount technology (SMT) assembly, eliminating the need for through-holes and enabling no-leads package configuration while maintaining PCB connectivity.
3Reliability
If pads are completely enclosed by molding, then package protection is improved, but thermal dissipation and electrical connectivity are reduced
Solution Approach 1:
The invention extracts the thermal dissipation and electrical connectivity function from the enclosed molded structure by providing pads that extend beyond the molding encapsulation. These exposed pads are specifically designed to remain outside the molding material, allowing direct contact with the PCB for both thermal sinking and electrical connection, while the majority of the lead frame and die remain protected within the molding for mechanical strength and environmental protection.
Data Source
AI summary
A lead frame includes a first side having a first die attach pad that is bondable to a die, and a second side that has a second die attach pad that is bondable to another die. The lead frame includes multiple leads on the edges of the lead frame to connect the die. As part of a no-leads device, such as a quad flat no leads (QFN) or dual flat no-leads (DFN), one of the die attach pads is used in binding to a die, and the other die attach pad is used for thermal dissipation and mounting to a structure such as printed circuit board (PCB).