Dual-Layer Inkjet Printhead Encapsulation for Wirebond Integrity

Solution Overview

Problem

Existing wirebond encapsulants in inkjet printheads provide inadequate chemical resistance while introducing undesirable thermo-mechanical stresses, leading to die-cracking and wirebond fracture.

Innovation Solution

A dual-layer encapsulant system with a softer first fill encapsulant minimizing mechanical linkage and a harder second fill encapsulant providing chemical resistance, reducing thermo-mechanical stresses and protecting wirebonds.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a relatively harder encapsulant material is used, then chemical resistance and mechanical robustness are improved, but thermo-mechanical stresses increase leading to die-cracking

Engineering Contradiction:

Improvechemical resistanceVSAvoidthermo-mechanical stresses

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The encapsulant is divided into two distinct layers: a first fill encapsulant with relatively low modulus of elasticity and a second fill encapsulant with relatively high modulus of elasticity. This segmentation allows each layer to perform its specialized function - the softer first layer minimizes mechanical linkage and thermo-mechanical stresses, while the harder second layer provides chemical resistance and mechanical robustness.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the encapsulant are given different mechanical properties. The first fill encapsulant (softer) is positioned to provide stress relief, while the second fill encapsulant (harder) is positioned to provide chemical protection. This local differentiation of material properties resolves the contradiction between needing hardness for chemical resistance and softness for stress minimization.

Inventive Principle:

Principle #3Local quality

2Strength

If a relatively harder encapsulant material is used, then mechanical robustness is improved, but wirebond fracture risk increases due to mechanical linkage

Engineering Contradiction:

Improvemechanical robustnessVSAvoidwirebond integrity

Core Design Contradiction:

StrengthVSReliability

Solution Approach 1:

The encapsulant is divided into two distinct layers: a first fill encapsulant with relatively low modulus of elasticity and a second fill encapsulant with relatively high modulus of elasticity. This segmentation allows each layer to perform its specialized function - the softer first layer minimizes mechanical linkage and thermo-mechanical stresses, while the harder second layer provides chemical resistance and mechanical robustness.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The first fill encapsulant acts as an intermediary layer between the wirebonds and the external environment. This softer intermediate layer reduces the transmission of mechanical stresses to the wirebonds, preventing wirebond fracture while still allowing the harder second layer to provide overall mechanical robustness.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Object-affected harmful factors

If a relatively softer encapsulant material is used, then thermo-mechanical stresses are minimized, but chemical resistance decreases

Engineering Contradiction:

Improvethermo-mechanical stressesVSAvoidchemical resistance

Core Design Contradiction:

Object-affected harmful factorsVSReliability

Solution Approach 1:

The encapsulant is divided into two distinct layers: a first fill encapsulant with relatively low modulus of elasticity and a second fill encapsulant with relatively high modulus of elasticity. This segmentation allows each layer to perform its specialized function - the softer first layer minimizes mechanical linkage and thermo-mechanical stresses, while the harder second layer provides chemical resistance and mechanical robustness.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different regions of the encapsulant are given different mechanical properties. The first fill encapsulant (softer) is positioned to provide stress relief, while the second fill encapsulant (harder) is positioned to provide chemical protection. This local differentiation of material properties resolves the contradiction between needing hardness for chemical resistance and softness for stress minimization.

Inventive Principle:

Principle #3Local quality

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 dual-layer encapsulant system effectively minimizes die-cracking and wirebond fracture by balancing mechanical and chemical protection, suitable for harsh environments.

Implementation Method 1

a first fill encapsulant having a relatively low modulus of elasticity

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 2

a second fill encapsulant having a relatively high modulus of elasticity

Methodology Applied

Scientific EffectElasticity: Elasticity

Data Source

PatentEP4196350B1Inkjet printhead having robust encapsulation of wirebonds

Publication Date: 2025.09.24 MEMJET TECH LTD

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Figure 3~4
Figure 5~6

AI summary

An electronic assembly includes a substrate having a die and PCB mounted thereon. Wirebonds interconnect bond pads of the die with contact pads of the PCB, each wirebond having a first end portion bonded to a respective bond pad, an opposite second end portion bonded to a respective contact pad and an intermediate section extending between the first and second end portions. A dam encapsulant encapsulates each of the first and second end portions, a first fill encapsulant contacts the substrate and the dam encapsulant; and a second fill encapsulant overlies the first fill encapsulant. The first fill encapsulant has a lower modulus of elasticity than the second fill encapsulant and the dam encapsulant.