Leadless Stack Bonding via Transient Liquid Phase Sintering
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Solution Overview
Problem
Current technologies face challenges in forming reliable, high-temperature bonds for leadless electronic components, particularly multi-layered ceramic capacitors, that can withstand solder reflow processes without compromising the termination or lead attachment, while minimizing microphonic noise and avoiding the use of banned materials like lead and cadmium.
Innovation Solution
The use of transient liquid phase sintering (TLPS) adhesives and materials, which form a metallurgical bond between electronic elements at relatively low initial process temperatures, achieving high melting points suitable for subsequent solder reflow processes, and reducing microphonic noise by eliminating the need for solder balls and allowing for the stacking of components without gaps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-based solders are used to attach components, then reliable bonding is achieved, but hazardous materials are used which are restricted by RoHS legislation
Solution Approach 1:
The patent changes the material composition parameters by using Pb-free solder alloys with specific compositions (e.g., Sn-Cu, Sn-Ag-Cu) that meet both reliability requirements and RoHS compliance. The solder alloy parameters are optimized to achieve appropriate melting points, wetting characteristics, and mechanical properties without lead content.
2Object-affected harmful factors
If SAC solders are used for Pb-free circuits, then RoHS compliance is achieved, but higher processing temperatures are required which approach the melting point of the solder
Solution Approach 1:
The patent applies different material compositions to different regions or layers of the solder joint. For example, intermetallic compound layers are formed with specific compositions (Cu6Sn5, Cu3Sn) that provide high-temperature stability, while the bulk solder maintains Pb-free composition for RoHS compliance. This local differentiation allows the joint to withstand reflow temperatures.
Solution Approach 2:
The solder joint is designed as a composite structure consisting of multiple phases and layers including the Pb-free solder matrix, intermetallic compound layers, and substrate metallization. This composite structure provides both RoHS compliance and the necessary thermal stability for high-temperature processing.
3Temperature
If high melting point materials like gold/germanium are used for attachments, then high temperature capability is achieved, but higher processing temperatures are required which prevent wider use in electronics
Solution Approach 1:
The patent optimizes the solder alloy composition parameters to achieve a balance between melting point and processability. By carefully selecting the ratios of Sn, Cu, Ag, and other elements, the solder achieves adequate high-temperature capability (melting point around 217-227°C for SAC305) while remaining manufacturable with standard reflow soldering processes.
4Temperature
If zinc and aluminum powder are used in solders, then higher temperature capability is achieved, but oxide films form on the surface which cause poor wettability
Solution Approach 1:
The patent applies fluxes and surface preparation treatments before soldering to prevent oxide film formation on zinc and aluminum-containing solder surfaces. The flux chemically removes oxides and maintains a clean, wettable surface during the soldering process, enabling reliable bonding despite the presence of high-temperature capable metals like Zn and Al in the solder composition.
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 technology provides robust, high-temperature bonds that maintain integrity during solder reflow, reduce microphonic noise, and allows for the stacking of electronic components with improved mechanical and electrical properties, suitable for high-temperature applications without the use of hazardous materials.
Implementation Method 1
forming a first layer of a first component of a transient liquid phase sintering conductive adhesive; forming a second layer of the first component of the transient liquid phase sintering conductive adhesive; contacting the first layer and the second layer with a second component of transient liquid phase sintering conductive adhesive; heating to a first temperature sufficient to form a first transient liquid phase sintering conductive layer
Data Source
AI summary
A method of forming a leadless stack comprising multiple components is provided. The method comprises forming an MLCC comprising a first capacitor external termination and a second capacitor external termination and forming an electronic element is formed comprising a first element external termination and a second element external termination. The MLCC and electronic component are are arranged in a stack with a TLPS bond between the first capacitor external termination and the first element external termination.