Tapered Via Conductor in Ceramic Multilayer Substrate

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Solution Overview

Problem

Ceramic multilayer substrates face challenges in suppressing contraction during firing, leading to potential gaps between via conductors and insulating layers, which can result in moisture ingress, electrochemical migration, and solder flash, especially when mounting high-density components.

Innovation Solution

A ceramic multilayer substrate design featuring a tapered surface-layer via conductor that penetrates through both ceramic layers, with the second layer containing materials that suppress thermal contraction, allowing direct connection to component terminals without land electrodes, and optimizing alumina and glass ingredient ratios to prevent gaps and enhance connection strength.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Manufacturing precision

If the insulating layers are made of glass ceramics with different contraction temperatures to suppress plane direction contraction, then the wiring electrode and via conductor positions are prevented from deviating, but the amount of contraction in the stacking direction is increased, causing via conductors to protrude from the surface

Engineering Contradiction:

Improveposition accuracy of wiring electrodes and via conductorsVSAvoidprotrusion of via conductors from surface

Core Design Contradiction:

Manufacturing precisionVSShape

Solution Approach 1:

The patent adjusts the contraction characteristics of the insulating layers by selecting glass ceramic materials with specific contraction starting temperatures and contraction end temperatures. The first insulating layer is designed to complete its contraction before the second insulating layer begins contracting, thereby controlling the overall contraction behavior to prevent via conductor protrusion while maintaining position accuracy.

Inventive Principle:

Principle #35Parameter changes

Solution Approach 2:

The patent applies different material compositions to different insulating layers (first insulating layer vs. second insulating layer) to achieve localized contraction control. Each layer has tailored thermal contraction properties that coordinate during firing to prevent both position deviation and via conductor protrusion.

Inventive Principle:

Principle #3Local quality

2Shape

If the via conductor sectional area is reduced on the uppermost surface side to prevent protrusion, then via conductor protrusion is suppressed, but the connection strength to mounted components is insufficient

Engineering Contradiction:

Improvesuppression of via conductor protrusionVSAvoidconnection strength to component terminals

Core Design Contradiction:

ShapeVSStrength

Solution Approach 1:

The patent optimizes the contraction temperature parameters of the insulating layers to control the firing process, ensuring that the via conductors maintain their intended shape and position without protruding, while preserving sufficient connection area for component mounting.

Inventive Principle:

Principle #35Parameter changes

3Strength

If land electrodes are formed in larger areas than via conductor end surfaces to improve connection strength, then connection strength is increased, but the area for mounting high-density components is reduced

Engineering Contradiction:

Improveconnection strength of land electrodesVSAvoidmounting density of components

Core Design Contradiction:

StrengthVSProductivity

Solution Approach 1:

The patent modifies the thermal contraction parameters of the insulating layers to eliminate gap formation during firing, thereby maintaining via conductor integrity and connection strength without requiring larger land electrodes, thus preserving mounting area for high-density components.

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

This design ensures sufficient connection strength for high-density components, prevents moisture ingress, and avoids electrochemical migration and solder flash by aligning the thermal contraction of the via conductor with the insulating layers, maintaining insulation integrity.

Implementation Method 1

at least the second ceramic layer contains a material suppressing thermal contraction of the surface-layer via conductor

Methodology Applied

Scientific EffectThermal contraction: Thermal Contraction

Implementation Method 2

aligning the thermal contraction of the via conductor with the insulating layers, maintaining insulation integrity

Methodology Applied

Scientific EffectThermal contraction: Thermal Contraction

Data Source

PatentUS9686872B2Ceramic multilayer substrate

Publication Date: 2017.06.20 MURATA MFG CO LTD

AI summary

In a ceramic multilayer substrate formed by stacking and firing a plurality of insulating layers, the insulating layer in an uppermost surface layer includes a ceramic layer, a contraction suppression layer stacked on the ceramic layer, and a surface-layer via conductor penetrating through the ceramic layer and the contraction suppression layer and having a tapered shape gradually tapering toward the lower layer side. The surface-layer via conductor has an end surface that is exposed from the contraction suppression layer forming the surface of the ceramic multilayer substrate, and that is directly connected to a terminal of a component mounted to the surface of the ceramic multilayer substrate. A weight ratio of alumina contained in the contraction suppression layer is set higher than a weight ration of alumina contained in the ceramic layer.