Leadless MLCC Stack Using Transient Liquid Phase Sintering
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Solution Overview
Problem
Current technologies for forming high-temperature bonds on electronic components, such as stacked leadless multi-layered ceramic capacitors, face challenges with reliability due to the need for high processing temperatures and the use of banned or costly materials like lead and gold, and fail to accommodate components of differing lengths without compromising the integrity of the bond.
Innovation Solution
The use of transient liquid phase sintering (TLPS) to form conductive layers on multilayered ceramic capacitors, allowing for low-temperature initial bonding followed by high-temperature metallurgical interconnects, which can withstand secondary reflow processes and accommodate components of varying lengths without the need for intimate surface contact or solder balls.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-based solders are used to attach components, then reliable bonds are formed, but hazardous substances are used which are restricted by RoHS legislation
Solution Approach 1:
The invention changes the material composition parameters by using Sn-Ag-Cu (SAC) lead-free solder alloys instead of traditional lead-based solders. This substitution maintains bonding reliability while eliminating hazardous lead content to comply with RoHS legislation.
Solution Approach 2:
The patent employs consumable sacrificial solder balls that are designed to be consumed during the bonding process. These SAC solder balls provide reliable lead-free bonds without requiring expensive alternative materials like gold or platinum.
2Temperature
If high melting point materials like gold/germanium or gold/silicon alloys are used for high temperature bonds, then high temperature capability is achieved, but processing temperatures must be raised above 350° C. which prevents wider use
Solution Approach 1:
The invention changes the temperature parameters by using SAC solder with a melting point of approximately 217-220° C., enabling bonding at lower temperatures (below 350° C.) compared to traditional high-temperature materials like gold/germanium alloys that require temperatures above 350° C.
Solution Approach 2:
The patent uses composite SAC solder alloy material comprising tin, silver, and copper in specific proportions. This composite material achieves optimal balance between melting point, strength, and processability, enabling reliable bonds at moderate temperatures without requiring expensive high-temperature materials.
3Reliability
If SAC solders are used for lead-free circuits, then lead-free bonding is achieved, but reflow temperatures must be about 260° C. and the contact material must sustain temperatures well above this which causes reliability issues
Solution Approach 1:
The invention optimizes the SAC solder alloy composition parameters (specific ratios of Sn, Ag, and Cu) to achieve a melting point that enables reflow at approximately 260° C. while maintaining adequate safety margin. The patent specifies controlled reflow temperatures to ensure reliable bonds without excessive thermal stress.
4Temperature
If zinc and aluminum powder are used in solder formulations, then higher temperature capability is achieved, but oxide films form on the surface which are associated with poor wettability
Solution Approach 1:
The invention changes the material composition by using SAC solder alloy (Sn-Ag-Cu) that inherently resists oxide film formation compared to zinc or aluminum-based solders. This composition provides good wettability and reliable bonding without the oxidation problems associated with reactive metals like zinc and aluminum.
5Adaptability or versatility
If components of differing lengths are assembled, then design flexibility is improved, but gaps must be left between components which increases assembly complexity
Solution Approach 1:
The patent introduces a compliant interconnect structure that acts as an intermediary between components of differing lengths. This compliant connection accommodates length variations and misalignments without requiring precise gap control, thereby simplifying the assembly process while maintaining design flexibility.
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
TLPS enables the formation of robust, high-temperature-resistant bonds with improved mechanical and electrical properties, reducing stress on components and allowing for the assembly of components with different lengths without gaps, thus enhancing the reliability and efficiency of electronic component attachment.
Implementation Method 1
a first transient liquid phase sintering conductive layer on the first side and in electrical contact with each first electrode; and a second transient liquid phase sintering conductive layer on the second side and in electrical contact with each second electrode
Data Source
AI summary
A stacked MLCC capacitor is provided wherein the capacitor stack comprises multilayered ceramic capacitors wherein each multilayered ceramic capacitor comprises first electrodes and second electrodes in an alternating stack with a dielectric between each first electrode and each adjacent second electrode. The first electrodes terminate at a first side and the second electrodes second side. A first transient liquid phase sintering conductive layer is the first side and in electrical contact with each first electrode; and a second transient liquid phase sintering conductive layer is on the second side and in electrical contact with each second electrode.