Position Member for Thin Semiconductor Package Warpage Control

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Solution Overview

Problem

Thin semiconductor packages face issues with warpage and die/pad flexing due to variations in molding compound thickness and mismatched thermal expansion coefficients, leading to assembly distortions and structural failures during the molding process.

Innovation Solution

Incorporating a position member under or above the die-attach pad in the semiconductor package to control the die's Z-position and prevent large variations during assembly, using a leadframe with lead terminals and bonding wires, and encapsulating with a molding compound to form a very thin semiconductor package.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of moving object

If a thin semiconductor package is designed to reduce package size, then the package thickness is reduced, but warpage and die/pad flexing increase due to insufficient molding compound coverage and CTE mismatch

Engineering Contradiction:

Improvepackage thicknessVSAvoidwarpage control

Core Design Contradiction:

Length of moving objectVSReliability

Solution Approach 1:

A position member is introduced as an intermediary element between the die-attach pad and the molding compound. This position member serves as a mediator that actively compensates for the insufficient support provided by the thin molding compound layer, preventing warpage and die/pad flexing while enabling the thin package design to proceed

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the structural parameters of the package by introducing a position member with specific thickness and material properties. This position member is designed with a thickness greater than the molding compound layer to provide adequate support, and its material is selected to match the CTE of the die-attach pad, thereby resolving the warpage issue through parameter optimization

Inventive Principle:

Principle #35Parameter changes

2Length of moving object

If the die and leadframe thickness are reduced to achieve thinner packages, then package size is reduced, but flexing during assembly process increases

Engineering Contradiction:

Improvedie thicknessVSAvoidresistance to flexing

Core Design Contradiction:

Length of moving objectVSStrength

Solution Approach 1:

The position member acts as a counterweight element that provides opposing support to the flexing forces acting on the thin die and leadframe during assembly. By positioning this support element directly beneath the die-attach pad, it creates a counterbalancing effect that prevents excessive flexing while allowing the thin-profile design to be maintained

Inventive Principle:

Principle #8Anti-weight (Counterweight)

3Length of moving object

If molding compound thickness is reduced to enable thinner packages, then package size is reduced, but variation in compound thickness increases causing warpage

Engineering Contradiction:

Improvemolding compound thicknessVSAvoidcompound thickness uniformity

Core Design Contradiction:

Length of moving objectVSManufacturing precision

Solution Approach 1:

The position member serves as an intermediary support structure that decouples the relationship between molding compound thickness and warpage control. By providing additional support beneath the die-attach pad, it allows the molding compound layer to be thinner while maintaining uniform thickness, as the position member compensates for the reduced compound coverage

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention optimizes the thickness parameter of the position member to be greater than the molding compound layer thickness. This parameter change ensures that even with reduced compound thickness, the combined structure maintains sufficient support to prevent warpage, thereby improving manufacturing precision

Inventive Principle:

Principle #35Parameter changes

4Device complexity

If existing leadframe designs are used without modification, then device complexity is reduced, but warpage and die displacement during molding cannot be adequately controlled

Engineering Contradiction:

Improveleadframe design complexityVSAvoiddie displacement control

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

Rather than redesigning the entire leadframe structure, the invention introduces a position member as a minimal intermediary element attached to the existing leadframe. This approach maintains the simplicity of the original leadframe design while adding the necessary functionality to control die displacement and warpage during the molding process

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS7919361B2Semiconductor package with position member

Publication Date: 2011.04.05 STMICROELECTRONICS INT NV

AI summary

The present disclosure provides a very thin semiconductor package including a leadframe with a die-attach pad and a plurality of lead terminals, a die attached to the die-attach pad and electrically connected to the lead terminals via bonding wires, a position member disposed upon the die and/or die-attach pad, and a molding material encapsulating the leadframe, the die, and the position member together to form the semiconductor package. The method for manufacturing a very thin semiconductor package includes disposing a first position member on one side of the die-attach pad of a leadframe, attaching a die onto the opposite side of the die-attach pad, optionally disposing a second position member on top of the die, electrically connecting the die to the lead terminals of the leadframe, and encapsulating the leadframe, the die, and the position member(s) together to form the very thin semiconductor package.