Power Semiconductor Encapsulation via Stepped Mold Cavity
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Solution Overview
Problem
The existing encapsulation resin used in transfer molding for power semiconductor devices faces challenges with high injection speed requirements, leading to increased flow resistance, instability in bonding between the die pad and insulating film, reduced dielectric withstand voltage, and the generation of resin burrs that impede heat dissipation.
Innovation Solution
A method involving a lead frame with a stepped portion in the lower mold cavity, allowing the encapsulation resin to flow downward and reduce resistance at the bent portion, stabilize bonding, and prevent resin burrs by pressing the die pad and insulating film, thereby enhancing surface pressure and heat dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If injection speed is increased to complete molding within restricted time, then productivity is improved, but flow resistance at bent portion increases causing die pad bonding instability and reduced dielectric withstand voltage
Solution Approach 1:
The mold cavity is segmented into a first cavity for the die pad and a second cavity for the power semiconductor element, allowing independent optimization of injection parameters for each component and reducing mutual interference during molding
Solution Approach 2:
A protrusion is added to the die pad in the thickness direction, creating a stepped structure that changes the injection flow path from horizontal to vertical, reducing flow resistance at the bent portion while maintaining bonding stability
2Productivity
If injection speed is increased to complete molding within restricted time, then productivity is improved, but surface pressure on power semiconductor element is reduced weakening bonding strength
Solution Approach 1:
The mold cavity is segmented into a first cavity for the die pad and a second cavity for the power semiconductor element, allowing independent optimization of injection parameters for each component
Solution Approach 2:
The die pad is pre-positioned on the lower mold with the protrusion extending into the second cavity, preparing the structure in advance to receive the power semiconductor element and encapsulation resin without requiring high surface pressure
3Productivity
If encapsulation resin flows horizontally at high speed, then productivity is improved, but resin burrs are generated on metal plate reducing heat dissipation
Solution Approach 1:
The injection flow is redirected from horizontal to vertical direction through the stepped cavity structure, causing resin to flow downward along the metal plate surface rather than horizontally, preventing burr formation while maintaining high injection speed
Solution Approach 2:
The protrusion on the die pad is designed in advance to extend into the second cavity, creating a natural flow guide that directs encapsulation resin away from the metal plate edges before injection begins
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 approach improves the yield and heat dissipation of power semiconductor devices by stabilizing the bonding between the die pad and insulating film, increasing dielectric withstand voltage, and inhibiting resin burr formation, which enhances the device's performance and reliability.
Implementation Method 1
the encapsulation resin is caused to flow downward from above the stepped portion toward the upper surface of the power semiconductor element
Implementation Method 2
An encapsulation resin used in transfer molding has a thermosetting property, is temporarily molten by heat and is thereafter set by chemical reaction
Implementation Method 3
is temporarily molten by heat
Implementation Method 4
is thereafter set by chemical reaction
Implementation Method 5
there is a need for the power semiconductor device to have the ability to dissipate heat from the element
Data Source
AI summary
A power semiconductor element is fixed on a die pad of the lead frame. A metal plate is bonded to a lower surface of the die pad via an insulating film. The inner lead etc. are disposed in a cavity between a lower mold and an upper mold and are encapsulated with an encapsulation resin. The lower mold has a stepped portion provided in a bottom surface of the cavity below the inner lead. A height of an upper surface of the stepped portion is larger than a height of an upper surface of the power semiconductor element disposed in the cavity. When an encapsulation resin is injected into the cavity, a lower surface of the metal plate is in contact with the bottom surface of the cavity, and the encapsulation resin flows downward from above the stepped portion toward the upper surface of the power semiconductor element.