LTCC Conductor Additive Segmentation for Lead Bonding

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Solution Overview

Problem

LTCC circuits face issues with poor lead bonding due to additives in the conductor metallization, which can lead to weak connections and loose leads when attempting to connect them to other circuitry.

Innovation Solution

A bonding metal layer of the same metal as the conductors, but devoid of additives, is deposited on top of the conductors to improve bonding performance, which can be cofired with the ceramic layers or applied post-firing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If additives are included in the conductor metallization to promote adhesion to the ceramic layer, then adhesion to the ceramic base layer is improved, but lead bonding performance deteriorates

Engineering Contradiction:

Improveadhesion to ceramic base layerVSAvoidlead bonding performance

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The conductor metallization is segmented into two distinct layers: a first conductor layer containing additives for ceramic adhesion, and a second conductor layer devoid of additives for lead bonding. This segmentation allows each layer to perform its specific function optimally without compromise.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the conductor metallization are assigned different compositions tailored to their specific functions. The first conductor layer (contacting ceramic) has additive-rich composition for adhesion, while the second conductor layer (contacting lead) has additive-free composition for bonding compatibility.

Inventive Principle:

Principle #3Local quality

2Reliability

If a bonding metal layer is deposited on top of the conductors to improve lead bondability, then lead bonding performance is improved, but device complexity increases

Engineering Contradiction:

Improvelead bonding performanceVSAvoidstructure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The bonding metal layer is merged with the second conductor layer by using the same metal composition. This integration eliminates the need for a distinct third layer, as the second conductor layer itself serves as the bonding surface, thereby improving lead bondability without significantly increasing structural complexity.

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

This solution enhances lead bondability by 10-20% in strength and reduces 'no stick' situations by up to 50%, ensuring a strong and reliable connection.

Implementation Method 1

A bonding metal layer is deposited on top of the conductors at predetermined locations

Methodology Applied

Scientific EffectDeposition: Deposition (physical)

Implementation Method 2

The ceramic layers are cofired at a temperature high enough to sinter the layers

Methodology Applied

Scientific EffectSintering: Sintering

Data Source

PatentUS7820490B2Method for LTCC circuitry

Publication Date: 2010.10.26 NORTHROP GRUMMAN SYSTEMS CORP

AI summary

An LTCC (low temperature cofired ceramic) structure which has conductors to which leads are to be bonded for connection to external circuitry. The conductors include additives to promote adhesion to the ceramic layer. The presence of these additives degrade bonding performance. For better bondability of the leads, a pure conductor metal layer, devoid of the additives is placed on the conductors in areas where leads are to be bonded. This pure conductor metal layer may be cofired with the stack of ceramic layers or may be post fired after stack firing.