Footed Power Package with Coplanar Leads and Heat Tab
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Solution Overview
Problem
Current power packages face limitations in low-profile, multi-lead capability, flexible manufacturing, and cost-effectiveness due to issues with lead bending, thermal resistance, and inflexible manufacturing processes, leading to inefficiencies in power dissipation and packaging density.
Innovation Solution
The development of a footed power package design featuring coplanar 'feet' at the bottom of the package, which are short conductors extending laterally for precise soldering, combined with a heat tab for improved thermal management, allowing for flexible lead placement and reduced inductance, and eliminating the need for lead bending machinery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional lead bending processes are used to create footed packages, then leads can be formed to fit PCB mounting requirements, but manufacturing complexity increases and coplanarity precision deteriorates
Solution Approach 1:
The leadframe is designed with pre-formed feet that extend laterally from the die pad area before packaging. This preliminary configuration eliminates the need for post-molding lead bending operations, ensuring precise coplanarity is achieved during the leadframe fabrication process rather than through complex mechanical forming operations after packaging.
Solution Approach 2:
The lead bending operation is extracted from the packaging process entirely. Instead of bending leads after they are enclosed in the plastic mold, the leads are pre-configured in their final footed configuration on the leadframe itself, separating the lead forming function from the packaging function and eliminating the associated complexity and precision issues.
2Temperature
If thicker leadframes are used to improve power dissipation capability, then thermal performance improves, but package height increases
Solution Approach 1:
The invention transitions from vertical heat dissipation through thick leadframes to lateral heat dissipation through extended feet. By spreading the thermal path horizontally across the PCB mounting surface through the footed configuration, the package maintains low height while achieving effective power dissipation through increased surface area contact with the PCB.
Solution Approach 2:
The leadframe is segmented into multiple feet extending from the die pad area, creating distributed thermal contact points. This segmentation allows heat to be dissipated across multiple locations on the PCB rather than requiring a single thick leadframe structure, achieving thermal performance without increased package height.
3Reliability
If injection molding is used to encapsulate the device, then protection during handling and shipping is improved, but manufacturing flexibility deteriorates
Solution Approach 1:
The leadframe is pre-configured with the final footed geometry and lead arrangements before the injection molding process. This preliminary formation of the lead structure allows the subsequent molding operation to simply encapsulate the pre-defined configuration, enabling easy adaptation to different package designs by modifying the leadframe rather than retooling the expensive molding equipment.
Solution Approach 2:
The invention applies different functional qualities to different parts of the package: the leadframe provides the mechanical and electrical structure with precise lead geometry, while the plastic mold compound provides only the protective encapsulation function. This separation allows the leadframe to be optimized for electrical performance and manufacturing flexibility while the plastic provides reliable protection, without the two functions being coupled in a way that reduces overall adaptability.
Data Source
AI summary
A method is disclosed of fabricating a power package which includes a heat tab extending from a die pad exposed on the underside of the package, which facilitates the removal of heat from the die to the PCB or other surface on which the package is mounted. The heat tab has a bottom surface coplanar with the flat bottom surface of the die pad and bottom surface of a lead. The lead includes a horizontal foot segment, a vertical columnar segment, and a horizontal cantilever segment facing the die pad. The heat tab may also have a foot. A die containing a power device is mounted on a top surface of the die pad and may be electrically connected to the lead using a bonding wire or clip. The die may be mounted on the die pad with an electrically conductive material, and the package may also include a lead that extends from the die pad and is thus electrically tied to the bottom of the die. The result is a package with a minimal footprint that is suitable for the technique known as “wave soldering” that is used in relatively low-cost printed circuit board assembly factories.