Flexible Circuit Cable Attachment Using Gold Bumps for Overlapping Bonds
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Solution Overview
Problem
Existing methods for attaching flexible circuit cables to a substrate, such as direct soldering, Anisotropic Conductive Film (ACF), and conductive epoxy, face challenges with overlapping cables, including wetting issues, co-planarity problems, and limited radio frequency (RF) bandwidth, especially in small assembly scenarios like optical sub-assemblies.
Innovation Solution
The method involves bonding multiple gold bumps on interconnection pads of the substrate to create columns that assist in solder or epoxy wetting and bonding, using a hot air reflow system to apply heat, and applying nonconductive underfill epoxy for mechanical strength, which reduces bridging and smearing risks and enhances RF performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If direct soldering is used to attach flexible circuit cables, then electrical connectivity is achieved, but the heat reflow impacts pre-attached chips or flexible circuit cables and causes wetting issues in overlapping scenarios
Solution Approach 1:
The patent introduces an intermediary bonding process between the flexible circuit cable and substrate that does not rely on high-temperature solder reflow. The method uses a bonding process that can be performed at lower temperatures, allowing attachment without adversely affecting pre-attached components while still achieving reliable electrical connectivity.
Solution Approach 2:
The patent changes the temperature parameter of the bonding process from traditional high-temperature soldering to a lower temperature process. This parameter change enables the attachment of flexible circuit cables without causing heat damage to pre-attached chips or cables, while maintaining electrical connectivity through alternative bonding mechanisms.
2Reliability
If Anisotropic Conductive Film (ACF) or Anisotropic Conductive Paste (ACP) is used, then electrical connectivity is achieved through compression, but high thermal temperature is required to cure the film which impacts pre-attached components
Solution Approach 1:
The patent fundamentally changes the temperature parameter from high-temperature curing (required by ACF/ACP) to a lower temperature bonding process. This allows the flexible circuit cable to be attached and cured at temperatures that do not adversely affect pre-attached components, while still achieving reliable electrical connectivity through the bonding process.
3Strength
If conductive epoxy is used for attachment, then bonding is achieved, but variance/planarity conditions and co-planarity issues arise with overlapping cables and pre-bent flexible circuit cables
Solution Approach 1:
The patent segments the bonding process into controlled stages with applied pressure at specific points in the sequence. This segmentation allows the bonding material to be distributed and pressed uniformly across the attachment area, achieving both strong bonding and good co-planarity even with overlapping cables and pre-bent flexible circuit cables.
Solution Approach 2:
The patent applies preliminary pressure control before final bonding to ensure proper co-planarity. By controlling the pressure application sequence and magnitude beforehand, the flexible circuit cable is positioned and bonded in a way that maintains co-planarity with the substrate, avoiding manufacturing precision issues.
4Reliability
If traditional attachment methods are used, then attachment is achieved, but limited reworkability and higher resistance than solder result
Solution Approach 1:
The patent changes the bonding parameters to create a bond that is stronger than traditional methods but maintains reworkability. By controlling the bonding temperature, pressure, and material composition, the attachment achieves high reliability while allowing for future rework or removal if needed, and provides lower resistance than traditional conductive epoxies.
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
This approach enables reliable attachment of overlapping flexible circuit cables with improved RF performance, increased mechanical strength, and reduced electrical resistance, suitable for high-density signal routing in limited spaces without impacting pre-attached components.
Implementation Method 1
A hot air reflow system is used to apply a first set of predetermined levels of heat to promote the bonding material to bond between the substrate and the first flexible circuit cable
Implementation Method 2
bonding material to promote the bonding material to bond between the substrate and the first flexible circuit cable... columns restrict dispersion of the bonding material... solder wets to the interconnection pads
Implementation Method 3
applying nonconductive underfill epoxy for mechanical strength... to provide mechanical strength
Data Source
AI summary
A method and apparatus for multiple flexible circuit cable attachment is described herein. Gold bumps are bonded on interconnection pads of a substrate to create a columnar structure and solder or conductive epoxy is dispensed on the flexible cable circuit. The substrate and flexible cable circuit are aligned and pressed together using force or placement of a weight on either the substrate or flexible cable circuit. Appropriate heat is applied to reflow the solder or cure the epoxy. The solder wets to the substrate pads, assisted by the gold bumps, and have reduced bridging risk due to the columnar structure. A nonconductive underfill epoxy is applied to increase mechanical strength.