Backside Electrical Connections for Printhead Integrated Circuits

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Solution Overview

Problem

Existing inkjet printheads face challenges with wirebond connections that protrude from the ink ejection face, affecting print maintenance and quality by preventing a fully planar surface and limiting the application of hydrophobic coatings.

Innovation Solution

The implementation of a printhead assembly with backside electrical connections using a connector film sandwiched between the ink supply manifold and printhead integrated circuits, eliminating the need for wirebond connections on the frontside and allowing for a fully planar ink ejection face, which is achieved through the use of through-silicon connectors and a tape-automated bonding (TAB) film.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If wirebond connections are used to connect printhead integrated circuits to external power/data supply, then electrical connections are established, but the wirebonds protrude from the ink ejection face and affect print maintenance and quality

Engineering Contradiction:

Improveelectrical connection reliabilityVSAvoidimpact on print maintenance and quality

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent inverts the conventional wirebonding approach by moving the electrical connection interface from the front side (ink ejection face) to the back side of the printhead integrated circuit. The connector film is positioned on the backside, and through-silicon connectors route electrical signals from the backside contact pads through the silicon substrate to the frontside circuitry, eliminating protruding wirebonds from the ink ejection face.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent transitions the electrical connection interface from a two-dimensional surface connection (wirebonds on the front face) to a three-dimensional through-substrate connection. Through-silicon connectors create vertical pathways through the silicon substrate, utilizing the third dimension (depth) to route connections from the backside to the frontside, thereby clearing the front surface of protruding elements.

Inventive Principle:

Principle #17Another dimension (Dimensionality change)

2Reliability

If wirebond connections are used, then electrical connections are provided, but the frontside face cannot be fully planar and hydrophobic coating application is limited

Engineering Contradiction:

Improveelectrical connection functionalityVSAvoidplanarity of ink ejection face

Core Design Contradiction:

ReliabilityVSShape

Solution Approach 1:

The patent inverts the connection architecture by placing all electrical connection interfaces on the backside of the printhead integrated circuit. The connector film with contact pads is positioned on the backside, and through-silicon connectors route signals through the substrate, leaving the front ink ejection face completely clear and planar for optimal coating application.

Inventive Principle:

Principle #13The other way round (Inversion)

Solution Approach 2:

The patent extracts the electrical connection interface from the frontside ink ejection face and relocates it entirely to the backside. By removing wirebond connections and their associated support structures from the front surface, the ink ejection face achieves full planarity, enabling uniform hydrophobic coating application across the entire surface.

Inventive Principle:

Principle #2Taking out (Extraction)

3Shape

If connector film is sandwiched between ink supply manifold and printhead integrated circuits, then backside electrical connections are achieved, but additional assembly steps are required

Engineering Contradiction:

Improveplanarity of ink ejection faceVSAvoidassembly process complexity

Core Design Contradiction:

ShapeVSDevice complexity

Solution Approach 1:

The patent merges the electrical connection function with the mechanical mounting structure by integrating the connector film into the assembly process. The connector film serves dual purposes: providing electrical connections through its conductive traces and serving as an adhesive interface between the printhead integrated circuit and the ink supply manifold, thereby reducing the number of separate components.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The connector film performs multiple functions simultaneously: it provides electrical connectivity through conductive traces, acts as an adhesive bonding layer between the printhead and manifold, and serves as a structural support for the backside connections. This multi-functionality reduces overall assembly complexity despite the backside connection approach.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS8101438B2Method of fabricating printhead integrated circuit with backside electrical connections

Publication Date: 2012.01.24 MEMJET TECH LTD

AI summary

A method of fabricating a printhead integrated circuit configured for backside electrical connections. The method comprises the steps of: (a) providing a wafer comprising a plurality of partially-fabricated nozzle assemblies on a frontside of the wafer and through-silicon connectors extending from the frontside towards a backside of the wafer; (b) depositing a conductive layer on the frontside of said wafer and etching to form an actuator for each nozzle assembly and a frontside contact pad over a head of each through-silicon connector; (c) performing further MEMS processing steps to complete formation of nozzle assemblies ink supply channels through-silicon connectors; and (d) dividing the wafer into individual printhead integrated circuits. Each printhead integrated circuit thus formed is configured for backside-connection to the drive circuitry via the through-silicon connectors the contact pads.