Stack Semiconductor Package Warpage Reduction via Flexible Substrate

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Solution Overview

Problem

Conventional stack semiconductor packages experience reliability issues due to warpage caused by temperature changes, particularly at solder melting temperatures, which affects the stacking and connectivity of semiconductor chips.

Innovation Solution

The use of a second semiconductor package with a substrate made of polyimide or polyethylene terephthalate, having a lower modulus and higher glass transition temperature than the first substrate, reduces warpage sensitivity and enhances reliability by providing improved heat resistance and flexibility, allowing for finer pitch stacking and increased chip density.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a conventional PCB is used as the substrate in stack semiconductor packages, then electrical connectivity and structural support are provided, but warpage occurs at solder melting temperature which deteriorates reliability

Engineering Contradiction:

Improvereliability of stack semiconductor packageVSAvoidwarpage of stack semiconductor package

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The patent changes the physical parameters of the substrate by selecting materials with specific modulus values (first substrate: 3-10 GPa, second substrate: 0.5-3 GPa) and glass transition temperatures (first substrate: 150-250°C, second substrate: 250-400°C). This parameter optimization reduces thermal expansion differences and warpage at solder melting temperatures, directly resolving the contradiction between reliability and structural stability.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent employs composite material strategy by using different substrate materials (polyimide, polyethylene terephthalate, or glass for first substrate; polyimide or polyethylene terephthalate for second substrate) with complementary properties. The combination of a higher-modulus first substrate and lower-modulus second substrate creates a balanced structure that minimizes overall warpage while maintaining electrical and mechanical functionality.

Inventive Principle:

Principle #40Composite materials

2Stability of the object's composition

If the modulus of the second substrate is reduced to improve flexibility and reduce warpage, then warpage sensitivity decreases, but structural strength may be compromised

Engineering Contradiction:

Improvewarpage sensitivityVSAvoidstructural strength of substrate

Core Design Contradiction:

Stability of the object's compositionVSStrength

Solution Approach 1:

The patent applies local quality by assigning different modulus values to different substrates in the stack structure. The first substrate has a higher modulus (3-10 GPa) for structural support, while the second substrate has a lower modulus (0.5-3 GPa) for warpage reduction. This localized differentiation allows each substrate to perform its specific function optimally without compromising overall structural integrity.

Inventive Principle:

Principle #3Local quality

3Temperature

If substrates with higher glass transition temperature are used to improve heat resistance, then reliability at high temperature improves, but material selection and manufacturing complexity increase

Engineering Contradiction:

Improveglass transition temperature of substrateVSAvoidmanufacturing complexity

Core Design Contradiction:

TemperatureVSEase of manufacture

Solution Approach 1:

The patent systematically changes the glass transition temperature parameter of substrate materials to exceed 250°C (first substrate) and 400°C (second substrate). This parameter threshold ensures that substrates maintain dimensional stability and do not undergo phase transitions during soldering processes, directly improving heat resistance and reliability while the specified material options keep manufacturing feasible.

Inventive Principle:

Principle #35Parameter changes

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

The solution effectively minimizes warpage in stack semiconductor packages, improving their reliability and enabling more efficient high-density chip stacking by utilizing the flexible and heat-resistant properties of polyimide or polyethylene terephthalate substrates.

Implementation Method 1

the warpage of the stack semiconductor package at the solder melting temperature

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

a glass transition temperature of the second substrate may be greater than a glass transition temperature of the first substrate

Methodology Applied

Scientific EffectGlass transition:

Data Source

PatentUS9041180B2Semiconductor package and method of manufacturing the semiconductor package

Publication Date: 2015.05.26 SAMSUNG ELECTRONICS CO LTD

AI summary

The stack package includes a first semiconductor package and a second semiconductor package. The first semiconductor package includes a first substrate having a first modulus and at least one semiconductor chip mounted on the first substrate. The second semiconductor package stacked on the first semiconductor package and includes a second substrate having a second modulus and at least one semiconductor chip mounted on the second substrate. The second modulus is less than the first modulus. Even in the event that the first semiconductor package is under severe warpage due to a temperature change, the flexible second substrate, which includes e.g., polyimide or poly ethylene terephthalate, of the second semiconductor package may be less sensitive to the temperature change, thereby improving reliability of the stack package.