Conductive Pad With Concave Sidewall Mitigates Thermal Stress

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Solution Overview

Problem

Structural defects such as cracks or delamination can occur between conductive pads and solder masks on semiconductor device packages due to mismatched coefficients of thermal expansion or warpage during thermal cycles, leading to reliability issues like short circuits.

Innovation Solution

A substrate with a patterned conductive layer featuring a conductive pad having a concave sidewall, designed to match the warpage contour, is used, along with a protection layer covering the pad, to mitigate crack issues by redistributing mechanical and thermal stress.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If traditional flat conductive pads are used, then manufacturing is simple, but cracks and delamination occur due to thermal expansion mismatch and warpage

Engineering Contradiction:

Improvestructural integrityVSAvoidpad structure complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The conductive pad is designed with a concave sidewall instead of a flat surface. This curved geometry allows the pad to conform to the warpage contour of the substrate, distributing thermal stress more evenly and preventing crack formation at the interface between the pad and solder mask.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The concave sidewall creates different surface geometries at different locations of the conductive pad. The curved portion contacts the substrate differently than the flat portions, allowing localized stress distribution that adapts to the warpage pattern and prevents delamination.

Inventive Principle:

Principle #3Local quality

2Reliability

If conductive pads with concave sidewalls are used, then stress intensity is reduced by up to 85%, but manufacturing complexity increases

Engineering Contradiction:

Improvecrack resistanceVSAvoidpad fabrication difficulty

Core Design Contradiction:

ReliabilityVSEase of manufacture

Solution Approach 1:

The invention changes the geometric parameters of the conductive pad from a flat surface to a concave sidewall structure. This parameter change fundamentally alters how stress is distributed across the pad, reducing stress intensity factors by up to 85% while maintaining electrical functionality.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If solder mask is applied over conductive pads, then protection is provided, but thermal expansion mismatch causes delamination at boundaries

Engineering Contradiction:

Improveprotection coverageVSAvoidbond strength

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The concave sidewall of the conductive pad creates a curved interface with the solder mask, which distributes the thermal expansion stresses more evenly across the boundary. This curved geometry prevents the concentration of stresses at sharp corners that would otherwise cause delamination.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Data Source

PatentUS10553527B2Substrate and semiconductor device package

Publication Date: 2020.02.04 ADVANCED SEMICON ENG INC

AI summary

A substrate including a dielectric layer and a patterned conductive layer adjacent to the dielectric layer is provided. The patterned conductive layer comprises a first conductive pad, the first conductive pad comprises a first portion having a first concave sidewall. The substrate further includes a protection layer disposed on the patterned conductive layer, and the protection layer covers the first portion of the first conductive pad.