Flip-Chip Underfill via Gravitational Aperture Filling

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Solution Overview

Problem

Existing flip-chip packaging methods face challenges in achieving a chip-scale package perimeter due to poor control of underfill material spread, leading to air pockets, incomplete fill, and voids, which affect reliability, and require significant clearance and expensive vacuum-assisted molding processes.

Innovation Solution

A method involving a dielectric substrate with apertures for gravitational alignment and introduction of low viscosity dielectric, allowing for precise underfill distribution and encapsulation with a dielectric polymer, reducing spacing between the integrated circuit and substrate to less than 100 microns and 2 millimeters, respectively, without the need for vacuum assistance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If underfill is dispensed along sides of die at elevated temperature to reduce viscosity, then underfill flows quickly between die and substrate, but spread control is poor and package size increases

Engineering Contradiction:

Improveunderfill flow speedVSAvoidunderfill spread control

Core Design Contradiction:

SpeedVSManufacturing precision

Solution Approach 1:

A release tape is introduced as an intermediary tool to control underfill dispensing. The tape is placed on the substrate and the die is pressed onto it, allowing underfill to be dispensed in a controlled manner through the tape's structure, preventing uncontrolled spreading while maintaining flow speed benefits

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The viscosity parameter of underfill is dynamically changed by controlling temperature during dispensing. The underfill is heated to reduce viscosity for easy flow, then cooled after dispensing to increase viscosity and stop spreading, providing both fast flow and precise control

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If clearance between die perimeter and substrate edge is increased to accommodate underfill flow, then underfill can spread freely, but package size increases significantly

Engineering Contradiction:

Improveunderfill dispensing easeVSAvoidpackage area

Core Design Contradiction:

Ease of manufactureVSArea of stationary object

Solution Approach 1:

Release tape serves as a mediator that enables underfill dispensing with minimal clearance. The tape's structure guides the underfill flow path and limits spread, allowing effective underfill application with only 0.5-2mm clearance instead of the traditional 3mm or more

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The underfill dispensing process is segmented into controlled stages using the release tape. The tape creates defined flow paths and stopping points, dividing the underfill application into manageable segments rather than allowing uncontrolled global spreading

Inventive Principle:

Principle #1Segmentation

3Reliability

If vacuum assisted molding is used to fill gaps between die and substrate, then voids are reduced, but process cost increases

Engineering Contradiction:

Improvevoid reductionVSAvoidprocess complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

Underfill application is performed as a preliminary action before molding, pre-positioning the die and filling potential void spaces with underfill material. This preliminary underfill layer prevents void formation during subsequent molding without requiring vacuum assistance

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The underfill material itself performs the void-prevention function that would otherwise require vacuum assisted molding. The underfill flows into and fills gap spaces between die and substrate, making the system self-sufficient without additional vacuum equipment or processes

Inventive Principle:

Principle #25Self-service

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 enables reliable chip-scale packaging with improved underfill control, reducing package size and eliminating voids, while maintaining package reliability and eliminating the need for expensive vacuum-assisted molding processes.

Implementation Method 1

gravitationally aligning the substrate/integrated circuit assembly such that the integrated circuit device is lower than said substrate; introducing a volume of a low viscosity dielectric into the at least one aperture

Methodology Applied

Scientific EffectGravity: Gravitation

Data Source

PatentUS7700414B1Method of making flip-chip package with underfill

Publication Date: 2010.04.20 UNISEM M BERHAD

AI summary

A method for the manufacture of a package to encapsulate at least one integrated circuit device includes the steps of: (1) providing a dielectric substrate having a first plurality of bond pads formed on a first side thereof and at least one aperture; (2) electrically interconnecting the integrated circuit device to the plurality of bond pads forming a substrate/integrated circuit device assembly; (3) gravitationally aligning the substrate/integrated circuit assembly such that the integrated circuit device is lower than said substrate; (4) introducing a volume of a low viscosity dielectric into the at least one aperture, wherein the volume is effective to coat a surface of the integrated circuit device and substantially fill the at least one aperture; and (5) encapsulating the integrated circuit device and the first side of said substrate with a dielectric polymer.