No-flow underfill for interposer frame package

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Solution Overview

Problem

The semiconductor industry faces challenges in manufacturing smaller packages with advanced packaging technologies like wafer level packaging (WLP) and package on package (PoP), particularly due to large pitch limitations and the risk of shorting between connectors, as well as thermal dissipation issues caused by mismatched coefficients of thermal expansion (CTEs) in conventional reflow processes.

Innovation Solution

The use of an interposer frame with through substrate holes (TSHs) and a no-flow underfill (NUF) layer, where the interposer frame is bonded to a substrate using heat from the semiconductor die and conductive layers, eliminating the need for a conventional reflow process and improving thermal matching between components.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If conventional reflow process is used to bond interposer frame to substrate, then bonding is achieved, but thermal dissipation issues occur due to mismatched coefficients of thermal expansion (CTEs)

Engineering Contradiction:

Improvebonding reliabilityVSAvoidthermal dissipation

Core Design Contradiction:

ReliabilityVSTemperature

Solution Approach 1:

The no-flow underfill material serves as an intermediary substance between the interposer frame and substrate, filling gaps and accommodating thermal expansion differences. This mediator layer prevents direct thermal stress transmission while maintaining mechanical bonding, thus resolving the CTE mismatch problem without requiring conventional reflow processes.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent changes the bonding process parameters by eliminating the conventional reflow process and instead using a no-flow underfill material that cures at lower temperatures. This parameter change allows bonding to occur without subjecting the assembly to high temperatures that cause thermal dissipation issues and CTE mismatch problems.

Inventive Principle:

Principle #35Parameter changes

2Area of stationary object

If pitch of connectors is reduced to enhance form factor, then form factor is improved, but risk of shorting between connectors increases

Engineering Contradiction:

Improveform factorVSAvoidshorting risk

Core Design Contradiction:

Area of stationary objectVSReliability

Solution Approach 1:

The no-flow underfill material acts as an insulating intermediary between closely spaced connectors, filling the spaces between them and providing electrical isolation. This allows connectors to be placed at reduced pitch while the underfill prevents shorting by maintaining proper insulation, thus enabling compact form factor without compromising reliability.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If conventional underfill material is used, then thermal expansion accommodation is achieved, but material flows and causes defects during reflow process

Engineering Contradiction:

Improvethermal expansion accommodationVSAvoidmaterial flow control

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

Instead of using conventional underfill materials that flow during reflow, the patent inverts the approach by using a no-flow underfill material that remains stable during bonding. This inversion eliminates the material flow problem while still providing thermal expansion accommodation through the material's elastic properties and gap-filling capability, thus improving manufacturing precision without sacrificing reliability.

Inventive Principle:

Principle #13The other way round (Inversion)

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 reduces the pitch of connectors, enhances the form factor, improves reliability by minimizing delamination and thermal cycling issues, and increases the yield of packaged structures, while also providing better insulation and strength to withstand drop tests.

Implementation Method 1

The no-flow underfill may be pushed aside to allow the bumps to bond together

Methodology Applied

Scientific EffectCapillary action: Capillary Action

Implementation Method 2

bonding the interposer frame to the substrate using heat from the semiconductor die and conductive layers

Methodology Applied

Scientific EffectThermal conduction: Conduction (thermal)

Data Source

PatentUS8946072B2No-flow underfill for package with interposer frame

Publication Date: 2015.02.03 TAIWAN SEMICONDUCTOR MANUFACTURING CO LTD

AI summary

Mechanisms of forming a package on package (PoP) package by using an interposer and an no-reflow underfill (NUF) layer are provided. The interposer frame improves the form factor of the package, enables the reduction in the pitch of the bonding structures. The NUF layer enables a semiconductor die and an interposer frame be bonded to a substrate by utilizing the heat on the connectors of the semiconductor die and on the connectors of the interposer frame for bonding. The heat provided by the semiconductor die and the interposer frame also transforms the NUF layer into an underfill. PoP structures formed by using the interposer frame and the NUF layer improve yield and have better reliability performance.