Flip Chip Backside VCSEL Package Footprint Reduction

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Solution Overview

Problem

Conventional VCSEL packages with frontside emitting VCSELs require wire bonding, increasing the footprint and hindering heat dissipation due to the active region's location on the top side, far from the heatsink.

Innovation Solution

A flip chip backside VCSEL package with a VCSEL pillar array, where a first metal contact is formed on the top and a second metal contact on the backside, allowing solder to be applied for direct mounting to a substrate package, eliminating the need for bond wires and reducing the footprint through a one-step reflow process.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If wire bonding is used to attach VCSEL device to external circuitry, then electrical connection is achieved, but the footprint of the VCSEL package assembly increases

Engineering Contradiction:

Improveelectrical connectionVSAvoidpackage footprint

Core Design Contradiction:

ReliabilityVSArea of stationary object

Solution Approach 1:

The patent extracts and eliminates the wire bonding process and bond pads from the VCSEL package assembly. By using a flip-chip mounting approach where the VCSEL device is directly soldered to the substrate, the bond wires and extended bond pads are removed, thereby reducing the package footprint while maintaining electrical connection functionality

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent inverts the conventional mounting approach by flipping the VCSEL device and mounting it upside down on the substrate. This inversion allows the bond pads to be located directly underneath the active region, enabling direct electrical connection through soldering without requiring wire bonds, thus reducing the package footprint

Inventive Principle:

Principle #13The other way round (Inversion)

2Ease of manufacture

If front side mounting is used for VCSEL device, then assembly process is simplified, but heat dissipation is reduced due to active region being far from heatsink

Engineering Contradiction:

Improveassembly processVSAvoidjunction temperature

Core Design Contradiction:

Ease of manufactureVSTemperature

Solution Approach 1:

The patent inverts the conventional front-side mounting approach by implementing flip-chip mounting where the VCSEL device is mounted upside down. This inversion places the active region directly above the heatsink, significantly improving thermal conduction and reducing junction temperature. The assembly process remains simplified through direct soldering without wire bonding

Inventive Principle:

Principle #13The other way round (Inversion)

3Reliability

If bond wires and bond pads are used in VCSEL package, then electrical connection is established, but device footprint is increased

Engineering Contradiction:

Improveelectrical connectionVSAvoiddevice footprint

Core Design Contradiction:

ReliabilityVSArea of moving object

Solution Approach 1:

The patent extracts and eliminates bond wires and extended bond pads from the package assembly by using flip-chip mounting. The VCSEL device is directly soldered to the substrate with bond pads located directly underneath the active region, removing the need for wire bonds and reducing the device footprint to the minimal area required for the VCSEL structure itself

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent merges the electrical connection function directly into the mounting structure by positioning bond pads directly underneath the active region and using solder to establish both mechanical and electrical connection simultaneously, eliminating the separate wire bonding step and reducing overall device footprint

Inventive Principle:

Principle #5Merging (Combining)

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 configuration simplifies assembly, reduces the package footprint, and enhances heat dissipation by eliminating bond wires and pads, thereby increasing the yield and reducing form factors.

Implementation Method 1

Solder is applied on each pillar of the VCSEL pillar array to flip chip mount the VCSEL pillar array to the substrate package

Methodology Applied

Scientific EffectSoldering: Soldering

Data Source

PatentUS11264780B2Flip chip backside emitting VCSEL package

Publication Date: 2022.03.01 NETFORCE OELABS INC

AI summary

A flip chip backside Vertical Cavity Surface Emitting Laser (VCSEL) package has a VCSEL pillar array. A first metal contact is formed over a top section of each pillar of the VCSEL pillar array. A second metal contact is formed on a back surface of the VCEL pillar array. An opening is formed in the second metal contact and aligned with the pillars of the VCSEL pillar array. Solder tip is applied on each pillar of the VCSEL pillar array to flip chip mount the VCSEL pillar array.