Optical Modulator Electrode Stress Relief for Wire Bonding
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Solution Overview
Problem
In optical modulators, particularly DP-QPSK modulators with LiNbO3 substrates, electrode deformation occurs due to bonding pressure, leading to impedance changes and manufacturing defects like short circuits, exacerbated by the miniaturization trend which increases the aspect ratio of electrodes, making it challenging to perform wire bonding without deformation.
Innovation Solution
Incorporating stress-relieving structures such as convex portions, concave portions, grooves, or metal bumps on the electrode surfaces to absorb bonding pressure, thereby preventing deformation and enhancing adhesion during wire bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If wire bonding is performed on electrodes with high aspect ratio (narrow and thick), then miniaturization and bandwidth increase are achieved, but electrode deformation occurs due to bonding pressure
Solution Approach 1:
The patent applies local quality by creating stress-relieving structures (convex portions, concave portions, grooves, or metal bumps) at specific locations on the electrode surface where bonding pressure is applied. These localized structural modifications allow stress concentration at designated areas while maintaining the overall high aspect ratio geometry of the electrode, thus preventing deformation of the critical bonding regions.
Solution Approach 2:
The stress-relieving structures are formed in advance before wire bonding to cushion and absorb the bonding pressure. The convex portions, concave portions, grooves, or metal bumps are pre-configured to deform elastically during bonding, absorbing the applied stress before it can reach and deform the main electrode body, thereby preventing impedance changes and manufacturing defects.
2Manufacturing precision
If bonding pressure is reduced to suppress electrode deformation, then electrode deformation is suppressed, but bonding peeling occurs
Solution Approach 1:
The stress-relieving structures are strategically positioned at the bonding locations to locally absorb bonding pressure. This allows the main electrode to maintain its structural integrity while the localized stress-relieving features deform elastically to accommodate the bonding process, ensuring both strong bonding and minimal overall deformation.
Solution Approach 2:
The stress-relieving structures act as intermediary elements between the bonding pressure and the main electrode. These intermediate structures (convex portions, concave portions, grooves, or metal bumps) deform first to absorb the bonding stress, preventing direct transmission of deformation forces to the electrode body while still maintaining sufficient bonding pressure for reliable wire bonding.
3Productivity
If electrode width is narrowed and thickness is increased to increase bandwidth, then bandwidth is increased, but aspect ratio increases making deformation more likely
Solution Approach 1:
The patent maintains the high aspect ratio geometry required for increased bandwidth by applying stress-relieving structures only at specific bonding locations. The electrode overall geometry (narrow and thick) is preserved to maximize bandwidth, while localized structural modifications at bonding areas provide stress relief during wire bonding, preventing deformation despite the high aspect ratio.
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 stress-relieving structures effectively suppress electrode deformation and impedance changes, reducing the likelihood of manufacturing defects like short circuits, even in high aspect ratio electrodes, while maintaining the miniaturization and performance requirements of optical modulators.
Implementation Method 1
at the time of bonding, compression pressure is applied while performing heating at the contact point between the metal wire and the electrode, so that the metal wire is bonded to the electrode. For this reason, in a bonding portion of the electrode, deformation occurs due to the stress generated by the compression pressure.
Data Source
AI summary
An optical modulator using an optical modulation element in which an optical waveguide and a plurality of electrodes for controlling light waves propagating through the optical waveguide are formed on a substrate, in which at least one stress relieving structure is provided on an upper surface of the electrode opposite to a surface of the substrate in order to relieve stress generated due to pressure applied at the time of wire-bonding of a metal wire.