Packaged Circuit Encapsulant Layout for Thermal Stress Relief

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Solution Overview

Problem

Packaged circuits experience package stress due to differences in thermal expansion coefficients of materials, leading to failure in reliability testing such as Q100 reliability testing, which limits their application in vehicles.

Innovation Solution

The application of multiple encapsulant layers with controlled thermal expansion coefficients, strategically spaced and partially cured, to reduce stress and enhance reliability, including a first encapsulant layer on the substrate, a second layer on the IC separated by a gap, and a third layer covering the gap, with all layers made from epoxy gel with a CTE below 25.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If multiple encapsulant layers with gaps are used, then stress is reduced and reliability is improved, but device complexity increases

Engineering Contradiction:

ImprovereliabilityVSAvoiddevice complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The encapsulant is divided into multiple separate layers (first encapsulant layer, second encapsulant layer, third encapsulant layer) with gaps between them, rather than using a single continuous encapsulant. This segmentation allows each layer to independently manage stress in different regions, reducing overall package stress while maintaining structural integrity

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The third encapsulant layer acts as an intermediary element that bridges and covers the gap between the first and second encapsulant layers. This intermediary layer provides stress relief and structural connection without creating a continuous rigid path, thereby reducing stress transmission while maintaining package coherence

Inventive Principle:

Principle #24Intermediary (Mediator)

2Stress or pressure

If encapsulant layers are spaced away from IC and substrate, then stress is reduced, but manufacturing precision requirements increase

Engineering Contradiction:

ImprovestressVSAvoidmanufacturing precision

Core Design Contradiction:

Stress or pressureVSManufacturing precision

Solution Approach 1:

The first and second encapsulant layers are applied and partially cured in predetermined positions spaced away from the IC and substrate before final assembly. This preliminary positioning and partial curing establishes precise spacing and alignment early in the manufacturing process, reducing stress while maintaining controlled precision requirements

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Different regions of the package have different encapsulant configurations - the first encapsulant layer contacts the substrate in specific areas, the second encapsulant layer contacts the IC in specific areas, and gaps are strategically positioned. This local differentiation optimizes stress distribution while managing manufacturing precision requirements in specific critical areas

Inventive Principle:

Principle #3Local quality

3Stress or pressure

If third encapsulant layer covers the gap, then stress distribution is improved, but manufacturing process complexity increases

Engineering Contradiction:

Improvestress distributionVSAvoidmanufacturing process complexity

Core Design Contradiction:

Stress or pressureVSDevice complexity

Solution Approach 1:

The third encapsulant layer is applied to cover the gap between the first and second encapsulant layers, merging these separate elements into a more integrated stress-management system. This combining approach improves stress distribution by creating a continuous encapsulant structure that spans across the gap region while managing the manufacturing process through sequential application

Inventive Principle:

Principle #5Merging (Combining)

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 described manufacturing process reduces stress, prevents silicon and glass cracks, wire lifting, and ensures packaged circuits pass Q100 reliability testing, making them suitable for vehicle environments without additional cost or reduced production throughput.

Implementation Method 1

One of the causes of package stress is contact between packaged circuit materials having different coefficients of thermal expansion (CTEs)

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Implementation Method 2

a first encapsulant layer in contact with the substrate and spaced away from the IC; a second encapsulant layer in contact with the IC and spaced away from the substrate

Methodology Applied

Scientific EffectViscoelasticity: Viscoelasticity

Data Source

PatentUS20250309019A1Packaged circuit and related vehicles

Publication Date: 2025.10.02 TEXAS INSTRUMENTS INC

AI summary

An apparatus includes: a substrate having a first set of bond pads; an integrated circuit (IC) having a second set of bond pads; bond wires between bond pads of the first set of bond pads and respective bond pads of the second set of bond pads; a first encapsulant layer in contact with the substrate and spaced away from the IC; a second encapsulant layer in contact with the IC and spaced away from the substrate, the second encapsulant layer separated from the first encapsulant layer by a gap; and a third encapsulant layer in contact with at least one of the first encapsulant layer and the second encapsulant layer, the third encapsulant layer at least partially covering the gap.