Optical Module Bump Bonding Layout for Dense Reliable Packaging
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Solution Overview
Problem
Conventional wire bonding in optical modules leads to increased size, reduced density, and compromised reliability due to the need for separate electrode pads and generation of backward waves, along with thermal stress and stress from wire bonding, which affects the joining portion of bumps.
Innovation Solution
An optical module design that uses Au bumps to electrically and mechanically connect the optical semiconductor element and insulating substrate, eliminating the need for wire bonding, and employs ultrasonic wave joining to reduce size and increase density while ensuring high reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If wire bonding is employed for electrical connection, then electrical connection can be established, but the module size increases and mounting density decreases
Solution Approach 1:
The patent extracts the wire bonding process and replaces it with bump bonding technology. By removing the wire bonding step and using direct bump connections between the optical semiconductor element and insulating substrate, the module size is reduced while maintaining electrical connection functionality. This extraction of the harmful wire bonding process resolves the contradiction between module size reduction and connection reliability.
Solution Approach 2:
The patent substitutes the mechanical wire bonding system with an ultrasonic bump bonding system. Instead of using wires and wire bonding tools, the invention uses ultrasonic waves to bond bumps directly to the substrate, replacing a multi-step mechanical process with a more compact ultrasonic bonding process that reduces overall module volume while improving reliability.
2Reliability
If wire bonding is performed onto the front surface, then electrical connection is achieved, but stress is applied to the bump joining portion causing it to break easily
Solution Approach 1:
The patent segments the electrical connection process into two separate stages: first, bump bonding is performed to join the optical semiconductor element to the insulating substrate; second, wire bonding is performed on the rear surface of the substrate away from the bump joining area. This segmentation prevents stress from wire bonding from affecting the bump joining portion, thereby improving reliability while managing process complexity through staged fabrication.
Solution Approach 2:
The patent moves the wire bonding operation to another dimension by performing it on the rear surface of the insulating substrate rather than the front surface. This spatial repositioning in the Z-dimension (thickness direction) allows wire bonding to occur without applying stress to the bump joining portions on the front surface, thus protecting the integrity of the critical bump connections.
3Area of stationary object
If separate electrode pads are provided for bump connection and wire bonding, then both functions are achieved, but the substrate area increases
Solution Approach 1:
The patent makes the electrode pads on the insulating substrate multi-functional by designing them to serve both bump connection and wire bonding purposes. The same electrode pad structure is used for both types of connections, eliminating the need for separate dedicated pads for each function. This universal design reduces the total substrate area required while maintaining reliable electrical connections through both bump and wire bonding methods.
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 design achieves a smaller, higher-density optical module with improved frequency characteristics and increased capacity, while maintaining high reliability by using Au bumps and ultrasonic wave joining to connect the semiconductor element and insulating substrate.
Implementation Method 1
a step of joining, by an ultrasonic wave, the bump and the electrode pad of the insulating substrate or the electrode pad of the semiconductor element while pressing the bump and the electrode pad
Data Source
AI summary
The present disclosure includes: an optical semiconductor element having a front surface on which an electrode pad is formed; an insulating substrate having a front surface and a back surface on which respective electrode pads are formed; and an Au bump with which the electrode pad on the back surface of the insulating substrate and the electrode pad of the semiconductor element are joined to each other. The insulating substrate is disposed such that the back surface thereof faces the front surface of the semiconductor element. The electrode pad on the back surface of the insulating substrate is connected via a through-hole to the electrode pad on the front surface of the insulating substrate.