Silver-Sintered Quartz Crystal Bonding for Stable Resonance
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Solution Overview
Problem
Quartz crystal oscillators experience reliability degradation due to bonding layers in high temperature, high shock, and high vibration applications, leading to resonance frequency drift over time, which is not adequately addressed by existing technologies.
Innovation Solution
A method of packaging a quartz crystal using a sintered silver paste bonding layer and an additional flexible bonding layer, where the sintered silver paste is formed by attaching the quartz crystal to a substrate in a substantially oxygen-free atmosphere, causing a positive drift in resonance frequency, while the flexible layer causes a negative drift, resulting in a net minimal frequency shift over time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bonding layers are used to attach the quartz crystal, then the bonding provides mechanical support and electrical connection, but the resonance frequency drifts over time in high temperature applications
Solution Approach 1:
The patent changes the material composition and processing parameters of the bonding layer by using silver paste with specific particle size distributions (bimodal or trimodal) and sintering at controlled temperatures (200-300°C) in oxygen-free or low-oxygen atmospheres. This creates a bonding layer with optimized thermal expansion characteristics that compensates for frequency drift, maintaining resonance frequency stability in high temperature applications.
Solution Approach 2:
The patent uses composite silver paste materials containing silver particles with multiple size distributions combined with organic vehicle materials. The sintered structure creates a composite bonding layer that provides both mechanical bonding and frequency stabilization through controlled thermal expansion properties, resolving the contradiction between bonding function and frequency stability.
2Reliability
If the quartz crystal is hermetically sealed in a package substrate, then the reliability is improved by protecting from environmental factors, but the manufacturing process complexity increases
Solution Approach 1:
The patent merges the bonding function and hermetic sealing function into a single integrated process. The silver paste is applied and sintered to create both the bonding layer and the hermetic seal simultaneously, eliminating the need for separate bonding and sealing steps. This reduces manufacturing complexity while maintaining high reliability through effective environmental protection.
3Manufacturing precision
If silver paste is sintered in oxygen-free atmosphere, then the frequency drift is reduced to positive values, but the manufacturing process becomes more complex
Solution Approach 1:
The patent introduces an intermediary atmosphere control system that provides oxygen-free or low-oxygen environment during sintering. This intermediary condition (controlled atmosphere) acts as a mediator between the silver paste and oxygen, preventing oxidation and enabling precise frequency control. The use of standard vacuum or inert gas atmospheres makes this intermediary approach practically implementable despite the added process step.
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
The approach significantly reduces resonance frequency drift, maintaining stability even after 4000 hours at 250°C, and provides robust bonding that withstands high shock pulses without failure, enhancing the reliability of quartz crystal oscillators in harsh environments.
Implementation Method 1
sintering the one or more silver paste layers in a substantially oxygen-free atmosphere and at a sintering temperature sufficient to cause sintering of the silver particles
Implementation Method 2
A crystal oscillator, e.g., a quartz crystal oscillator, vibrates at a stable frequency by being distorted by an electric field when voltage is applied to an electrode near or on the crystal. This property is known as electrostriction or inverse piezoelectricity.
Implementation Method 3
hermetically sealing the quartz crystal in the package substrate
Data Source
AI summary
The disclosed technology generally relates to packaging a quartz crystal, and more particularly to bonding a quartz crystal using sintering silver paste. In one aspect, a method of packaging a quartz crystal comprises attaching a quartz crystal to a package substrate using one or more silver paste layers comprising silver particles. The method additionally comprises sintering the silver paste in a substantially oxygen-free atmosphere and at a sintering temperature sufficient to cause sintering of the silver particles. The sintering is such that the quartz crystal exhibits a positive drift in resonance frequency of the quartz crystal over time. The method further comprises hermetically sealing the quartz crystal in the package substrate.