Matrix Leadframe Tie-Bar Bends for Balanced Mold Flow

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Solution Overview

Problem

As the number of rows in a matrix-format leadframe increases, it becomes challenging to balance the flow of encapsulation material to each mold cavity during the transfer molding process, leading to issues such as uneven material distribution and potential defects like wire sweep and mold voids.

Innovation Solution

Incorporating a mold flow control structure within the leadframe units, where the internal tie bar portion is cut and bent out of the plane to form an obtuse angle with the die pad, allowing for controlled adjustment of the acute angle and length of the bent portion to balance the flow of encapsulation material across multiple mold cavities.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If the number of rows in a matrix-format leadframe increases to enhance packaging capacity, then productivity is improved, but mold flow balancing becomes difficult leading to manufacturing defects

Engineering Contradiction:

Improvepackaging capacityVSAvoidmold flow balancing

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

The patent applies local quality by introducing a bend in the tie bar at a specific location within the mold cavity. This bend creates a localized flow control structure that modifies the mold flow characteristics in that specific region, allowing for balanced material distribution across multiple rows of cavities without compromising the overall packaging capacity

Inventive Principle:

Principle #3Local quality

Solution Approach 2:

The patent utilizes another dimension by bending the tie bar out of its original planar configuration. This three-dimensional modification adds a vertical component to the tie bar structure, creating a flow control element that manages mold material distribution in a multi-row matrix format while maintaining the horizontal packaging density

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Productivity

If the number of rows in a matrix-format leadframe increases to enhance packaging capacity, then productivity is improved, but the likelihood of defects like wire sweep and mold voids increases

Engineering Contradiction:

Improvepackaging capacityVSAvoiddefect rate

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The patent applies preliminary action by pre-configuring the tie bar with a bend before the molding process. This pre-established flow control structure proactively manages the mold material flow pattern, preventing wire sweep and mold void defects before they can occur during the injection process

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent converts the potential harm of increased defect risk associated with multi-row matrices into a benefit by using the tie bar bend as a flow control feature. The bend, which might seem like a structural modification, actually serves to balance mold flow and reduce defects, transforming a potential weakness into a strength

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

Data Source

PatentUS11862540B2Mold flow balancing for a matrix leadframe

Publication Date: 2024.01.02 STMICROELECTRONICS SDN BHD

AI summary

A frame includes leadframe units arranged in a matrix. Each leadframe unit has a die pad and tie bars connected to and extending from the die pad. Each tie bar includes an internal tie bar portion and an external tie bar portion. The internal tie bar portion of at least one tie bar includes a cut separating a part of the internal tie bar portion from the external tie bar portion. An out-of-plane bend in that part forms a mold flow control structure.