Semiconductor Package Encapsulation with Two-Step Overmolding
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Solution Overview
Problem
Current semiconductor manufacturing processes face issues with internal voids and wire sweeping during the molding of resin or epoxy molding compounds, particularly in high-density packages like Quad-Flat Packages (QFP) Super-Super High Density (SSHD), where existing solutions either increase voids or are cost- and time-demanding.
Innovation Solution
A two-step encapsulation process involving film-assisted molding to form a receiving cavity for a first resin mold, closing the space between die pads and leads, followed by a second overmolding with a molding compound, using techniques like laser-induced forward transfer or liquid mold dispensing to minimize wire sweeping and void formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a single-step injection molding process is used, then manufacturing simplicity is maintained, but internal voids and wire sweeping occur due to resin flow in the mold cavity
Solution Approach 1:
The molding process is divided into two distinct steps: first molding the encapsulation body with wires embedded, then overmolding with a second resin. This segmentation allows the first resin to be injected at lower pressure to avoid wire sweeping, while the second resin fills remaining cavities to eliminate voids, thereby resolving the contradiction between process simplicity and manufacturing precision.
Solution Approach 2:
The first molding step performs the preliminary action of embedding wires in the encapsulation body before the final overmolding step. This preliminary encapsulation protects wires from sweeping during subsequent handling and positioning, while the second overmolding step completes the encapsulation and eliminates voids, thus maintaining both ease of manufacture and manufacturing precision.
2Manufacturing precision
If center top gate molding technology is used, then internal voids formation is reduced, but critical wire sweeping occurs on lateral sides
Solution Approach 1:
The molding process is segmented into two steps where the first molding uses conventional gate positioning to avoid lateral wire sweeping, while the second overmolding step addresses void formation. This segmentation allows each step to optimize for its specific function, resolving the contradiction between void reduction and wire protection.
Solution Approach 2:
The first molding step performs the preliminary action of encapsulating wires in a protective resin matrix before the second overmolding step. This preliminary encapsulation prevents wires from being swept by lateral resin flow, while the second step's overmolding action fills voids without causing wire displacement.
3Quantity of substance
If low viscosity resin is used to flow through high-density wire mesh, then wire permeability is improved, but resin flows in the space between die pad and leads causing defects
Solution Approach 1:
The first molding step performs the preliminary action of injecting resin through the wire mesh at controlled viscosity and pressure to embed wires without allowing resin to intrude between die pad and leads. The second overmolding step then completes the encapsulation, ensuring complete filling without wire sweeping or resin intrusion defects.
Solution Approach 2:
The process uses parameter changes by controlling resin viscosity and injection pressure in the first molding step to allow sufficient flow through the wire mesh while preventing intrusion between die pad and leads. The second overmolding step uses different parameters to complete encapsulation, resolving the contradiction between resin flow through wires and preventing resin intrusion.
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 effectively reduces both internal voids and wire sweeping issues, ensuring the semiconductor devices are substantially exempt from these defects while maintaining process efficiency and cost-effectiveness.
Implementation Method 1
a first encapsulation step wherein a first mass of encapsulation material is transferred onto the at least one semiconductor die arranged on said die pad and onto said pattern of electrically conductive wires to form a core portion of the encapsulation, with the electrically conductive wires retained in position by the first mass of encapsulation material
Implementation Method 2
a second encapsulation step wherein a second mass of encapsulation material is molded onto the core portion of the encapsulation to provide a shell portion of the encapsulation around the core portion
Implementation Method 3
using techniques like laser-induced forward transfer or liquid mold dispensing to minimize wire sweeping and void formation
Data Source
AI summary
One or more semiconductor dice are arranged on a die pad of a leadframe having an array of electrically conductive leads around the die pad. A pattern of electrically conductive wires is provided to couple the semiconductor die or dice with electrically conductive leads in the array around the die pad. An encapsulation of insulating material is provided to encapsulate the semiconductor die or dice arranged on the die pad and the pattern of electrically conductive wires. Providing the encapsulation comprises: a first encapsulation step wherein a first mass of encapsulation material is transferred onto the semiconductor die or dice arranged on the die pad and onto the pattern of electrically conductive wires to form a core portion of the encapsulation that fully encapsulates the die or dice and the electrically conductive wires, that are thus retained in position by the first mass of encapsulation material, and a second encapsulation step wherein a second mass of encapsulation material is molded onto the core portion of the encapsulation to provide a shell portion of the encapsulation around the core portion of the encapsulation.