Surface-Mount Semiconductor Package Layout for Low-Profile Wave Soldering
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Solution Overview
Problem
Existing semiconductor packages face challenges in achieving low-profile dimensions, maintaining coplanarity, efficient heat dissipation, and flexible manufacturing processes that support both wave-solder and reflow assembly, while also requiring costly and inflexible equipment setups.
Innovation Solution
A leadframe design that integrates die pads and leads, allowing for flexible manufacturing of surface-mount packages with improved coplanarity and thermal dissipation, compatible with both wave-solder and reflow assembly, and eliminating the need for package-specific mold cavity tools.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional leaded packages are used, then wave-solder assembly is enabled, but package height is large and coplanarity is poor
Solution Approach 1:
The leadframe is segmented into distinct functional zones: die pad region, lead regions, and support regions. This segmentation allows independent optimization of each zone - the die pad can be thin for low profile while leads extend outward for soldering, resolving the contradiction between low height and wave-solder compatibility
Solution Approach 2:
The invention transitions from three-dimensional gull-wing lead configurations to a two-dimensional planar layout where leads extend laterally from the die pad in the same plane. This dimensional change eliminates the vertical height component while maintaining the necessary lead extensions for wave-solder assembly
2Ease of operation
If lead bending is performed to achieve coplanarity, then wave-solder compatibility is improved, but manufacturing complexity increases
Solution Approach 1:
Coplanarity is achieved through preliminary design of the leadframe geometry rather than post-manufacturing bending operations. The leads are pre-formed in the correct planar configuration during leadframe fabrication, eliminating complex bending steps and reducing manufacturing complexity
Solution Approach 2:
The mechanical lead bending process is replaced by a design-based solution where the leadframe structure itself provides the necessary coplanarity. This substitution eliminates the need for mechanical forming equipment and associated complexity
3Manufacturing precision
If package-specific mold cavity tools are used, then manufacturing precision is improved, but equipment cost and flexibility worsen
Solution Approach 1:
A universal leadframe design serves multiple package types and manufacturing requirements. The same leadframe structure can be used across different package configurations and assembly methods (wave-solder and reflow), eliminating the need for package-specific tooling while maintaining precision through standardized design features
4Length of stationary object
If low-profile design is implemented, then package height is reduced, but heat dissipation capability worsens
Solution Approach 1:
The heat dissipation function is extracted from the vertical dimension and relocated to the planar domain. Large surface area heat sink structures extend laterally from the die pad in the same plane, providing effective thermal management without increasing package height
Solution Approach 2:
Thermal management transitions from vertical heat sinking to lateral heat spreading. The heat dissipation structures are arranged in the planar direction rather than extending vertically, resolving the contradiction between low profile and heat dissipation capability
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
The solution enables the production of surface-mount packages that are low-profile, thermally efficient, and cost-effective, with improved manufacturing flexibility and reduced equipment requirements, addressing the limitations of current leaded and leadless packages.
Implementation Method 1
a first laser beam, which is normally moved in a series of parallel adjacent scans in the areas between the packages... a second laser beam is used to remove the metal conductors
Implementation Method 2
the plastic 'mold compound' is injected into a mold chamber at an elevated temperature... before cooling and curing into a solid plastic
Implementation Method 3
Solder 8A, covering flat portion 3A and electrically connecting conductor 1A and semiconductor die 4 to PCB conductive trace 7A
Data Source
AI summary
A variety of footed and leadless semiconductor packages, with either exposed or isolated die pads, are described. Some of the packages have leads with highly coplanar feet that protrude from a plastic body, facilitating mounting the packages on printed circuit boards using wave-soldering techniques.