Multi-Pitch Lead Frame for Power FET Reliability
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Solution Overview
Problem
Current packaging designs for power field effect transistors (FETs) lead to the deterioration of electrical connections between the device and a printed circuit board (PCB) due to concentrated current flow through narrow lead portions, causing solder joint damage and reducing the device's lifespan.
Innovation Solution
The use of a lead frame with non-etched leads, where thicker leads made of non-solder metal are coupled to a first lead frame using non-solder material, and both lead frames are encapsulated in molding, distributing current over a wider surface area and avoiding half-etching issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If traditional lead frames with etched leads are used, then manufacturing precision is improved, but the electrical connection reliability deteriorates due to concentrated current flow through narrow lead portions
Solution Approach 1:
The lead frame is divided into multiple segments: a first lead frame with etched leads for precise die attachment, and a second lead frame with thicker non-etched leads for robust electrical connections to the PCB. This segmentation allows each segment to optimize for its specific function, resolving the contradiction between manufacturing precision and connection reliability.
Solution Approach 2:
The patent transitions from a single-plane lead frame design to a multi-dimensional structure where leads are stacked in layers. The first lead frame lies in a first plane, while the second lead frame with thicker leads extends in a second plane, creating a three-dimensional lead arrangement that distributes current flow across multiple dimensions and reduces concentration effects.
2Length of moving object
If thinner leads are used to achieve finer pitch, then device miniaturization is improved, but the current carrying capacity deteriorates causing solder joint damage
Solution Approach 1:
The lead system is segmented into two distinct sets: thin leads in the first lead frame that achieve fine pitch for device miniaturization, and thick leads in the second lead frame that provide high current carrying capacity. The thin leads connect the die to the thick leads, which then connect to the PCB, allowing each segment to be optimized for its specific requirement.
Solution Approach 2:
The first lead frame with thin leads acts as an intermediary between the die and the second lead frame with thick leads. It transfers the fine-pitch connection requirement to the thin leads while transferring the high-current requirement to the thick leads, mediating between the conflicting requirements of miniaturization and current carrying capacity.
3Reliability
If solder is used to attach leads to PCB, then electrical connection is improved, but the lifespan deteriorates due to solder joint deterioration from concentrated current
Solution Approach 1:
The patent changes the physical parameters of the leads connecting to the PCB by using significantly thicker leads in the second lead frame. This parameter change increases the cross-sectional area for current flow, reducing current density and heat generation at the solder joints, thereby extending the lifespan of the solder connections while maintaining reliable electrical connectivity.
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 configuration mitigates the deleterious effects on solder joints and the structural integrity of the packaged device, extending its operational life and reducing manufacturing costs by distributing current evenly and avoiding solder-related damages.
Implementation Method 1
an electroplated layer stacked on the first non-solder metal plating
Data Source
AI summary
In some examples, a system comprises a die having multiple electrical connectors extending from a surface of the die and a lead coupled to the multiple electrical connectors. The lead comprises a first conductive member; a first non-solder metal plating stacked on the first conductive member; an electroplated layer stacked on the first non-solder metal plating; a second non-solder metal plating stacked on the electroplated layer; and a second conductive member stacked on the second non-solder metal plating, the second conductive member being thinner than the first conductive member. The system also comprises a molding to at least partially encapsulate the die and the lead.