Two-Step Leadframe Encapsulation for Void-Free Wire Bond Packaging
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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 compound, particularly in packages like Quad-Flat Package (QFP) Super-Super High Density (SSHD) where traditional solutions are not applicable due to high-density wire mesh, leading to device failure.
Innovation Solution
A two-step encapsulation process is employed, where a first step uses film-assisted molding with techniques like laser-induced forward transfer or liquid mold dispensing to encapsulate the core region containing wires, followed by a second step of conventional overmolding to form a shell portion, effectively reducing voids and wire sweeping without displacing the wires.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional injection molding is used to encapsulate the semiconductor device, then the molding process can be completed in a single step, but internal voids and wire sweeping occur due to resin flow in the mold chase cavity
Solution Approach 1:
The single-step injection molding process is divided into two distinct steps: first molding the core portion containing the wires, then molding the shell portion. This segmentation allows the first resin to encapsulate and protect the wires from sweeping, while the second resin completes the encapsulation without causing voids or wire displacement.
Solution Approach 2:
The core portion is molded first to preliminarily protect the wires before the shell portion is added. This preliminary action ensures that wires are already encapsulated and secured when the second resin is injected, preventing wire sweeping during the subsequent molding step.
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 core portion is molded first with a configuration that prevents wire sweeping, then the shell portion is added. This avoids the wire sweeping issue that occurs with center top gate molding while still reducing void formation through the two-step process.
Solution Approach 2:
The core portion is molded preliminarily to protect wires from sweeping before the shell portion is added. This preliminary protection ensures wire connection integrity is maintained throughout the complete encapsulation process.
3Manufacturing precision
If a first resin with low viscosity is dispensed to go through the high-density mesh of wires, then the resin can flow through the wire mesh, but the resin flows in the space between die pad and leads causing unwanted effects
Solution Approach 1:
A film is introduced to define the boundaries of the core portion, preventing resin leakage between the die pad and leads. The film acts as a barrier that guides the low-viscosity resin through the wire mesh while containing it within the desired encapsulation region.
Solution Approach 2:
The film serves as an intermediary element that mediates between the low-viscosity resin and the wire mesh structure. It allows the resin to flow through the wire mesh for proper encapsulation while preventing the harmful leakage into spaces between die pad and leads.
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 significantly reduces internal voids and wire sweeping issues, ensuring the semiconductor device is protected without compromising the integrity of the wire connections, making it suitable for high-density packages like QFP-SSHD.
Implementation Method 1
a film is used to form a receiving cavity for a first resin mold, closing the space between die pad and leads
Implementation Method 2
film-assisted molding, where a film is used to form a receiving cavity for a first resin mold
Implementation Method 3
these effects may be more evident at the last filled cavity/cavities in the arrangement due to an increased EMC viscosity
Data Source
Figure 1~3
Figure 4~5A
Figure 5B~5C
AI summary
One or more semiconductor dice (14) are arranged on a die pad (12A) of a leadframe (12) having an array of electrically conductive leads (12B) around the die pad (12A). A pattern of electrically conductive wires (16) is provided to couple the semiconductor die or dice (14) with electrically conductive leads (12B) in the array around the die pad (12A). An encapsulation of insulating material (18A, 18B) is provided to encapsulate the semiconductor die or dice (14) arranged on the die pad (12A) and the pattern of electrically conductive wires. Providing the encapsulation comprises: a first encapsulation step wherein a first mass of encapsulation material (18A) is transferred onto the semiconductor die or dice (14) arranged on the die pad (12A) and onto the pattern of electrically conductive wires (16) to form a core portion (100, 18A) of the encapsulation that fully encapsulates the die or dice (14) and the electrically conductive wires (16), that are thus retained in position by the first mass of encapsulation material (18A), and a second encapsulation step wherein a second mass of encapsulation material (18B) is molded onto the core portion (100, 18A) of the encapsulation to provide a shell portion (200, 18B) of the encapsulation around the core portion (100, 18A) of the encapsulation.