Variable Thickness Lead Frame for Power Semiconductor Devices
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Solution Overview
Problem
Existing molded resin-sealed power semiconductor devices face issues with thermal deformation, stress generation, and increased costs due to low lead frame rigidity, restricted heatsink manufacturing, and high wire bonding requirements, which limit size reduction and cost efficiency.
Innovation Solution
A power semiconductor device design featuring a lead frame with a thick central portion and thinner external wire and catch portions, allowing for improved thermal isolation without a stepped heatsink, reduced deformation, and cost-effective fabrication using materials with high thermal conductivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the lead frame rigidity is secured by the external wire portion and catch portion being held, then deformation in the vicinity of the semiconductor element due to soldering is prevented, but the molded resin protrudes beyond the exposed surface of the lead frame, requiring a step in the heatsink and increasing device complexity
Solution Approach 1:
The lead frame is designed with different thicknesses in different regions: a thick portion for mounting the semiconductor element to provide rigidity and prevent deformation during soldering, and thin portions for the external wire and catch portion to allow the molded resin to cover them completely, eliminating the need for heatsink steps
2Shape
If the lead frame is corrected so as to be flat inside a molding die when molding, then the lead frame flatness is improved, but large stress is generated in the semiconductor element and solder, shortening lifespan
Solution Approach 1:
The lead frame is pre-formed with the correct flat shape and dimensional stability before molding, using a precisely controlled stamping process that ensures the lead frame maintains its intended geometry without requiring correction during molding, thereby preventing stress generation in the semiconductor element
3Ease of manufacture
If the lead frame is made with constant thickness to simplify fabrication, then manufacturing ease is improved, but deformation occurs due to thermal contraction when rigidity is low
Solution Approach 1:
The lead frame employs variable thickness design with a thick portion (e.g., 0.8-1.2mm) at the semiconductor element mounting area to provide high rigidity and prevent thermal contraction deformation, while thinner portions (e.g., 0.3-0.5mm) are used for the external wire and catch portion to reduce material usage and allow complete coverage by molded resin
4Quantity of substance
If multiple pieces of wire bonding are used to increase allowable current, then current capacity is improved, but size and cost increase
Solution Approach 1:
The patent uses a single thick lead frame portion with increased cross-sectional area to carry higher current, replacing the need for multiple parallel wire bonds. This parameter change in the lead frame dimensions allows a single bonding structure to achieve the current capacity that would otherwise require multiple wire bonds, reducing device size and complexity
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 design enhances reliability, reduces stress, and lowers production costs by enabling the use of extruded aluminum or copper heatsinks, while increasing layout flexibility and cooling efficiency without the need for additional insulation steps.
Implementation Method 1
a lead frame having a thick portion on which the power semiconductor element is mounted and a thin portion thinner than the thick portion
Data Source
AI summary
Freedom of layout is increased, and a small, low-priced molded resin-sealed power semiconductor device is obtained. A molded resin-sealed power semiconductor device includes a power semiconductor element, a lead frame having a thick portion on which the power semiconductor element is mounted and a thin portion thinner than the thick portion, an inner lead that electrically connects the power semiconductor element and lead frame, and a molded resin that seals the power semiconductor element, lead frame, and inner lead.