Stacked Leadframe Tie Bar and Mold Cavity Bar Arrangement
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Solution Overview
Problem
Complex integrated circuit devices with multiple chip modules and system in package arrangements face challenges in achieving a small footprint while maintaining reliability and efficient electrical connections, as traditional leadframe designs often result in larger footprints due to their planar nature.
Innovation Solution
The use of multiple leadframes arranged in a stacked formation with an alternative die attach pad tie bar arrangement and an adjusted manufacturing process that includes a customized mold with cavity bar protrusions to prevent mold flash and enhance structural support, allowing for a more compact and reliable package design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If traditional planar leadframe designs are used, then manufacturing is simple, but footprint area is large
Solution Approach 1:
The patent transitions from a traditional planar (2D) leadframe arrangement to a three-dimensional stacked configuration. Multiple leadframes are positioned at different vertical levels (z-axis) above the die, with tie bars extending vertically to connect them. This dimensional change allows electrical connections to be made in three dimensions rather than constrained to a single plane, significantly reducing the horizontal footprint area while maintaining all necessary electrical interconnects.
Solution Approach 2:
The patent divides the leadframe structure into multiple separate leadframes stacked vertically rather than using a single planar leadframe. Each leadframe can be independently designed and manufactured, then stacked and connected via tie bars. This segmentation allows for optimized electrical routing in each layer and reduces the overall footprint by distributing connections across multiple vertical levels.
2Area of stationary object
If multiple leadframes are stacked, then footprint is reduced, but mold flash removal becomes difficult
Solution Approach 1:
The patent introduces asymmetry in the tie bar configuration by selectively positioning tie bars at specific corners of the stacked leadframes rather than uniformly at all corners. This asymmetric arrangement creates intentional gaps or access points in the mold flash formation, allowing mold flash to be more easily removed from specific locations while maintaining the structural integrity and electrical connectivity of the stacked leadframe assembly.
3Reliability
If tie bars are added for structural support, then reliability improves, but manufacturing complexity increases
Solution Approach 1:
The patent employs asymmetric tie bar placement where tie bars are positioned at specific corners of the stacked leadframes based on structural needs rather than uniform distribution. This selective positioning provides adequate structural support and reliability while minimizing the total number of tie bars required, thereby reducing manufacturing complexity compared to a symmetric all-corners configuration.
Solution Approach 2:
The patent applies tie bars locally at specific positions where structural support is most needed in the stacked leadframe assembly, rather than uniformly across all positions. This localized approach ensures reliability at critical stress points while reducing overall structural complexity and material usage in regions where support is less critical.
Data Source
AI summary
A semiconductor chip package having multiple leadframes is disclosed. Packages can include a first leadframe having a first plurality of electrical leads and a die attach pad having a plurality of tie bars, a second leadframe generally parallel to the first leadframe and having a second plurality of electrical leads, and a mold or encapsulant. Tie bars can be located on three main sides of the die attach pad, but not the fourth main side. Gaps in the first and second plurality of electrical leads can be enlarged or aligned with each other to enable the elimination of mold flash outside the encapsulated region, which can be accomplished with mold cavity bar protrusions. Additional components can include a primary die, a secondary die, an inductor and/or a capacitor. The first and second leadframes can be substantially stacked atop one another, and one or both leadframes can be leadless leadframes.