MLCC Lead Frame Attachment via Flexible Silver Adhesive
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Solution Overview
Problem
Multi-layered ceramic capacitors (MLCCs) are susceptible to cracking due to thermal stress caused by coefficient of thermal expansion (CTE) mismatches, particularly between nickel plating layers and the ceramic body, leading to spalling defects during reflow attachment to lead frames.
Innovation Solution
Eliminating the plating layers and applying a thin solderable silver coating over a flexible silver conductive adhesive to enhance soldering and provide thermal shock protection, while using copper or silver undercoats in electrical contact with internal electrodes to reduce CTE mismatch-induced stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If nickel plating layers are applied to the MLCC for solder adhesion, then solder attachment capability is improved, but thermal stress induced cracking and spalling defects occur due to CTE mismatch between the plating layers and ceramic body
Solution Approach 1:
The patent removes the problematic nickel plating layer from the MLCC structure. By eliminating the rigid plating layer that causes CTE mismatch, the invention extracts the harmful element while maintaining solder attachment capability through alternative means (silver conductive adhesive with flexible termination), thereby preventing thermal stress cracking and spalling defects
Solution Approach 2:
The invention changes the material composition and physical properties of the termination layer by using a silver conductive adhesive with flexible termination instead of rigid nickel plating. This parameter change in material flexibility and CTE compatibility resolves the contradiction by maintaining solder adhesion while eliminating thermal stress-induced damage
2Reliability
If rigid plating layers are used to ensure electrical contact, then electrical conductivity is maintained, but crack propagation occurs during thermal cycling
Solution Approach 1:
The patent employs a flexible termination layer made of silver conductive adhesive that can accommodate thermal expansion and contraction. This flexible film structure maintains electrical contact stability while absorbing thermal stresses, preventing crack propagation during thermal cycling by allowing controlled deformation rather than rigid fracture
3Ease of manufacture
If multiple plating layers are applied to enhance soldering, then solder adhesion is improved, but device complexity and manufacturing steps increase
Solution Approach 1:
The patent combines the functions of multiple plating layers (adhesion promoter, barrier layer, and solderable surface) into a single silver conductive adhesive layer with flexible termination. This merging eliminates the need for multiple sequential plating steps, reducing device complexity while maintaining or improving solder adhesion through the adhesive's inherent bonding properties
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 significantly reduces crack propagation and spalling defects, enhancing the capacitor's thermal cycling resistance and hermeticity by absorbing thermal and mechanical stresses through flexible layers, thus preventing electrical continuity disruptions.
Implementation Method 1
cracking due to a mismatch in the Coefficient of Thermal Expansion (CTE) of various components. The thermal mismatch causes stresses when subjected to temperature cycling or thermal shock
Implementation Method 2
A flexible silver conductive adhesive is applied over the copper undercoat... The flexible termination provides an extra level of protection against thermal shock cracking
Implementation Method 3
A thin second coating of solderable silver is applied over the flexible silver conductive adhesive to enhance soldering
Implementation Method 4
a first copper undercoat is in electrical contact with the conductive internal electrodes... A first lead is in electrical contact with the first copper undercoat with a first solder between the first lead and the first copper undercoat
Data Source
AI summary
A capacitor with improved lead frame attachment is described wherein the improved lead frame attachment mitigates defects. The capacitor comprises parallel conductive internal electrodes of alternating polarity with a dielectric between the conductive internal electrodes. A first copper undercoat is in electrical contact with the conductive internal electrodes of a first polarity and a second copper undercoat is in electrical contact with conductive internal electrodes of a second polarity. A first lead is in electrical contact with the first copper undercoat with a first solder between the first lead and the first copper undercoat. A second lead is in electrical contact with the second copper undercoat with a second solder between the second lead and the second copper undercoat.