Silver-Bonded Quartz Crystal Packaging for Frequency Drift Stability
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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 challenging to address effectively.
Innovation Solution
A method of packaging a quartz crystal using a sintered silver paste bonding layer and an additional flexible bonding layer, such as epoxy or polyimide, to create a hermetically sealed package that stabilizes the resonance frequency by causing shifts in opposite frequency directions, thereby reducing or eliminating drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional bonding layers are used to attach the quartz crystal, then the manufacturing process is simple, but the resonance frequency drifts over time in high temperature applications
Solution Approach 1:
The patent changes the bonding temperature parameter from conventional lower temperatures to high temperature sintering (above 200°C), which transforms the bonding layer material properties and eliminates frequency drift by creating a stable, low-outgassing bonding interface that maintains resonance frequency stability in high temperature applications
Solution Approach 2:
The patent uses a composite bonding approach combining sintered silver particles with glass frit or ceramic materials, creating a multi-phase composite bonding layer that provides both strong mechanical bonding and thermal stability, preventing resonance frequency drift while maintaining manufacturability
2Strength
If high temperature sintering is used to improve bonding reliability, then the bonding strength increases, but the manufacturing process becomes more complex
Solution Approach 1:
The patent merges the bonding process with the existing reflow soldering process used for attaching other components to the substrate, allowing the sintering of the bonding layer to occur simultaneously with standard PCB assembly operations, thereby increasing bonding strength without adding separate manufacturing steps
Solution Approach 2:
The patent introduces a specially formulated silver paste containing organic vehicles and fluxes as an intermediary material that enables low-cost, atmospheric pressure sintering without requiring complex vacuum equipment or specialized furnaces, making high temperature bonding accessible in standard manufacturing environments
3Reliability
If traditional bonding materials are used, then the process is straightforward, but the quartz crystal experiences frequency drift under shock and vibration
Solution Approach 1:
The patent applies local quality by creating a sintered bonding layer with localized high-density silver particle clusters that provide enhanced mechanical anchoring specifically at the quartz crystal contact points, while maintaining overall bonding layer flexibility to accommodate shock and vibration without frequency drift
Solution Approach 2:
The patent performs preliminary sintering of the bonding layer before final quartz crystal assembly, pre-establishing a mechanically stable bonding interface that can withstand subsequent shock and vibration events, eliminating the need for additional mechanical reinforcement structures
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 solution achieves a net resonance frequency drift of less than +/-200 ppm after 4000 hours at 250°C, withstanding shock pulses and maintaining mechanical and thermal integrity, 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
When the field is removed, the quartz, which oscillates in a precise frequency, generates an electric field as it returns to its previous shape, and this can generate a voltage
Implementation Method 3
The silver paste bonding layer and the flexible bonding layer are configured to cause shifts in a resonance frequency of the quartz crystal in opposite frequency directions
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.