Optical Transceiver Lid Alignment via Spherical Tacking Pads
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Solution Overview
Problem
Existing methods for hermetically sealing components in optical transceiver modules are costly and prone to failures due to lid shifting during the reflow process, which can result in non-wetting and damage to wire bonds, and are limited by temperature constraints.
Innovation Solution
A hermetic sealing system with temporary and permanent attachment/pre-alignment elements ensures the lid is securely positioned during soldering, using surface tension to align the lid permanently and an additional epoxy attachment to maintain the seal, while also preventing cracks in the dielectric layer through tapered patterned metal edges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional hermetic sealing methods are used, then the components are protected from the environment, but the cost increases and the process becomes complex
Solution Approach 1:
The sealing process is divided into two distinct stages: temporary attachment using spherical tacking pads for alignment, and permanent attachment using an annular sealing ring for hermetic sealing. This segmentation allows each stage to be optimized independently, simplifying the overall process while maintaining reliability.
Solution Approach 2:
The lid is temporarily attached to the submount assembly before the actual hermetic sealing process. This preliminary action ensures proper alignment and positioning of the lid relative to the submount assembly, preventing misalignment during the permanent sealing process and eliminating the need for complex alignment mechanisms.
2Ease of manufacture
If the lid is not temporarily attached during reflow, then the process is simpler, but the lid shifts causing non-wetting and wire bond damage
Solution Approach 1:
The lid is temporarily attached to the submount assembly before the actual hermetic sealing process. This preliminary action ensures proper alignment and positioning of the lid relative to the submount assembly, preventing misalignment during the permanent sealing process and eliminating the need for complex alignment mechanisms.
Solution Approach 2:
The spherical tacking pads provide a cushioning mechanism that absorbs misalignment forces during the reflow process. The spherical shape allows for self-alignment while the temporary attachment prevents excessive movement, protecting the wire bonds and ensuring proper wetting during sealing.
3Reliability
If the lid is temporarily attached, then lid shifting is prevented, but additional process steps are required
Solution Approach 1:
The temporary attachment function and the permanent sealing function are merged into a single integrated sealing structure. The same lid and substrate interface serves both alignment purposes (via spherical tacking pads) and hermetic sealing purposes (via annular sealing ring), eliminating the need for separate alignment fixtures or additional process equipment.
Solution Approach 2:
The spherical tacking pads are designed to be temporary and are removed or discarded after serving their alignment purpose. This allows the use of simple, inexpensive temporary attachment elements that can be easily removed without affecting the permanent seal or requiring complex retrieval mechanisms.
4Ease of manufacture
If metal edges are sharp, then manufacturing is easier, but cracks form in the dielectric layer
Solution Approach 1:
The metal layer is given different qualities at different locations: the bulk metal maintains its standard properties for electrical conductivity, while the edges are specifically tapered to reduce stress concentration. This local modification at the edges prevents crack formation in the dielectric layer without affecting the overall manufacturing process or electrical performance.
Solution Approach 2:
The geometry parameter of the metal layer edges is changed from sharp (90-degree angles) to tapered (gradual slopes). This parameter change reduces the stress concentration factor at the edges, preventing crack initiation in the dielectric layer while maintaining ease of manufacture through standard fabrication techniques.
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 provides a reliable, cost-effective hermetic seal that prevents lid shifting and ensures the integrity of the seal, addressing temperature limitations and reducing the risk of cracks in the dielectric layer, thus enhancing the operational stability of optical transceiver modules.
Implementation Method 1
temporary attachment elements, such as spherical tacking pads, which temporarily hold the lid in position during the reflow process
Implementation Method 2
permanent attachment elements, such as an annular sealing ring, which form a hermetic seal between the lid and the submount assembly
Implementation Method 3
The tapered edges of the metal layer prevent cracks from occurring in the dielectric layer
Data Source
AI summary
In an optical transceiver module, the bottom surface of the lid is temporarily attached to the top surface of the submount assembly in a pre-alignment position prior to performing the solder flowing process in order to prevent the lid from shifting position during the solder flowing process. The solder flowing process is then performed to melt the solder. When the solder melts, the surface tension of the melted solder pulls the lid into its ultimate, or permanent, aligned position. The solder is then cooled, causing it to harden, thereby securing the lid to the submount assembly in its ultimate, permanently aligned position. The hardened solder between the top surface of the submount assembly and the bottom surface of the lid forms a hermetic seal that encloses components on the transmit side of the transceiver module in a hermetically-sealed environment.