Image Sensor Packaging Hollow Cavity Stress Isolation

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Solution Overview

Problem

The existing wafer level chip size packaging technology faces issues with the rewiring layer detaching from the contact pad due to stress generated by thermal expansion and contraction of solder mask ink during reflow soldering and reliability testing, leading to defective chips.

Innovation Solution

A packaging method that involves forming V-shaped cutting trenches and openings on the wafer surface, filling these trenches with photosensitive ink to create a hollow cavity, and exposing the rewiring layer through holes in the ink to prevent direct contact and stress on the rewiring layer.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the opening is completely filled with solder mask ink, then the cutting trench and opening are protected and insulated, but thermal expansion and contraction of the solder mask ink generates stress that causes the rewiring layer to detach from the contact pad

Engineering Contradiction:

Improveprotection and insulation of cutting trench and openingVSAvoidattachment strength of rewiring layer to contact pad

Core Design Contradiction:

Ease of manufactureVSReliability

Solution Approach 1:

The patent introduces a hollow cavity as an intermediary space between the solder mask ink and the rewiring layer. This cavity acts as a buffer zone that prevents direct contact between the stress-generating solder mask ink and the sensitive rewiring layer, thereby eliminating the stress transmission that causes detachment while still maintaining the protective and insulating functions of the solder mask ink.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The hollow cavity is formed in advance before the solder mask ink is applied, creating a pre-prepared buffer space. This beforehand cushioning structure anticipates and prevents the stress problem by providing a physical separation zone that absorbs thermal expansion forces before they can reach the rewiring layer, thus preventing detachment before it occurs.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

2Ease of manufacture

If the opening is completely filled with solder mask ink, then protection and insulation are achieved, but the stress from thermal expansion causes defective chips

Engineering Contradiction:

Improveprotection and insulationVSAvoidchip yield

Core Design Contradiction:

Ease of manufactureVSProductivity

Solution Approach 1:

The hollow cavity serves as a mediator that allows the solder mask ink to fulfill its protective and insulating functions without transmitting harmful stress to the rewiring layer. This intermediary structure enables the manufacturing process to proceed with complete filling of the opening while preventing the formation of defective chips, thus improving chip yield.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent converts the potential harm of complete filling (stress generation) into a benefit by using the filled space to create the hollow cavity structure. The solder mask ink completely fills the opening as intended for protection and insulation, but the designed hollow cavity within this filled structure transforms the potential stress source into a stress-isolating buffer, thereby improving yield.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 method effectively prevents the rewiring layer from detaching from the contact pad, improving the yield and reliability of the image sensing chip package by forming a hollow cavity between the opening and the photosensitive ink.

Implementation Method 1

applying a photosensitive ink on the second surface of the wafer, to completely fill the V-shaped cutting trenches with the photosensitive ink, cover the openings with the photosensitive ink, and form a hollow cavity between each of the openings and the photosensitive ink

Methodology Applied

Scientific EffectPhotopolymerization: Photopolymerisation

Implementation Method 2

a stress is generated by thermal expansion and contraction of the solder mask ink in the subsequent reflow soldering and reliability testing

Methodology Applied

Scientific EffectThermal expansion: Thermal Expansion

Data Source

PatentUS10283483B2Packaging method and package structure for image sensing chip

Publication Date: 2019.05.07 CHINA WAFER LEVEL CSP

AI summary

A packaging method and package structure for an image sensing chip are provided. The method includes: providing a wafer including a first surface and a second surface opposite to the first surface, where the wafer has multiple image sensing chips arranged in a grid, each having an image sensing region and contact pads arranged on a side of the first surface of the wafer; forming openings extending towards the first surface on the second surface of the wafer, to expose the contact pads; forming V-shaped cutting trenches extending towards the first surface on the second surface of the wafer; and applying a photosensitive ink on the second surface of the wafer, to completely fill the V-shaped cutting trenches, cover the openings, and form a hollow cavity between each of the openings and the photosensitive ink.