Flexible Circuit Cable Attachment Using Gold Bump Columns
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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 reflow solder or cure epoxy, and applying nonconductive underfill epoxy for mechanical strength, while the gold bumps provide standoff height and reduce bridging risks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If direct soldering is used to attach flexible circuit cables, then electrical connectivity is achieved, but heat reflow impacts previously attached cables or chips
Solution Approach 1:
The patent segments the attachment process into multiple stages with different temperature profiles. Each flexible circuit cable is attached at a controlled temperature that does not exceed the thermal tolerance of previously attached components, enabling sequential attachment without mutual interference
Solution Approach 2:
The patent changes the temperature parameter dynamically during the attachment process. By controlling the reflow temperature to be below the damage threshold of pre-attached chips and cables, the method achieves soldering connectivity while protecting sensitive components from thermal damage
2Reliability
If ACF or ACP process is used for flexible circuit cable attachment, then electrical connectivity is achieved through conductive particles, but high thermal temperature is required to cure the film which impacts pre-attached components
Solution Approach 1:
The patent divides the attachment process into separate steps: first attaching flexible circuit cables at low temperature to avoid thermal damage, then applying ACF/ACP and curing at elevated temperature. This segmentation allows each step to occur under optimal conditions without interfering with previously attached components
Solution Approach 2:
The patent performs preliminary attachment of flexible circuit cables using low-temperature methods before applying the ACF/ACP process. This preliminary action ensures that heat-sensitive components are already in place and protected, so subsequent high-temperature curing does not damage them
3Strength
If conductive epoxy is used for flexible circuit cable attachment, then bonding is achieved, but variance in planarity and limited RF bandwidth occur
Solution Approach 1:
The patent uses a composite approach combining solder or conductive epoxy for electrical connectivity with nonconductive underfill epoxy for mechanical support. This composite structure provides both strong bonding and improved RF performance by ensuring planarity and reducing signal interference
Solution Approach 2:
The patent introduces nonconductive underfill epoxy as an intermediary material between the flexible circuit cable and substrate. This intermediary provides mechanical strength and planarity while being electrically nonconductive, thus improving RF bandwidth by reducing signal interference
4Productivity
If overlapping flexible circuit cables are attached sequentially, then high density signal routing is achieved, but wetting issue occurs between cable and substrate due to gap formed by previous cable
Solution Approach 1:
The patent uses nonconductive underfill epoxy as a mediator material that fills the gap between overlapping flexible circuit cables and the substrate. This intermediary enables proper solder wetting by providing a continuous bonding path while maintaining the high-density overlapping configuration
Solution Approach 2:
The patent applies local quality enhancement by using underfill epoxy specifically in the gap regions between overlapping cables. This localized approach ensures proper wetting and bonding only where needed, maintaining signal routing density while solving the wetting issue in critical areas
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, addressing the limitations of previous methods by ensuring effective bonding and high-density signal routing in limited spaces.
Implementation Method 1
A first set of predetermined levels of heat is applied to promote the bonding material to bond between the substrate and the first flexible circuit cable
Implementation Method 2
the column restricts dispersion of the bonding material
Implementation Method 3
applying nonconductive underfill epoxy for mechanical strength
Data Source
Figure 1~2C
Figure 3
Figure 4~6
AI summary
A method and apparatus for multiple flexible circuit cable attachment is described herein. Gold bumps (405, 505, 605, 610, 1610, 1910, 1920) are bonded on interconnection pads (210, 410) of a substrate (200, 400, 500, 600, 1305, 1320, 1605, 1805, 1905, 2045, 2210, 2260) to create a columnar structure and solder or conductive epoxy is dispensed on the flexible circuit cable (220, 230, 1300, 1325, 1600, 1705, 1800, 1900, 1915, 2005, 2010, 2030, 2040, 2265). The substrate (200, 400, 500, 600, 1305, 1320, 1605, 1805, 1905, 2045, 2210, 2260) and flexible circuit cable (220, 230, 1300, 1325, 1600, 1705, 1800, 1900, 1915, 2005, 2010, 2030, 2040, 2265) are aligned and pressed together using force or placement of a weight (2050, 2205, 2255, 2300) on either the substrate (200, 400, 500, 600, 1305, 1320, 1605, 1805, 1905, 2045, 2210, 2260) or flexible circuit cable (220, 230, 1300, 1325, 1600, 1705, 1800, 1900, 1915, 2005, 2010, 2030, 2040, 2265). Appropriate heat is applied to reflow the solder or cure the epoxy. The solder wets to the interconnection pads (210, 410) of the substrate (200, 400, 500, 600, 1305, 1320, 1605, 1805, 1905, 2045, 2210, 2260), assisted by the gold bumps (405, 505, 605, 610, 1610, 1910, 1920), and have reduced bridging risk due to the columnar structure. A nonconductive underfill epoxy is applied to increase mechanical strength.