Package reliability is the technical field that evaluates and guarantees whether functions can be maintained under the expected operating environment and period.

It covers every way something can fail:

・Does it fail electrically?

・Does it crack mechanically?

・Does it degrade due to heat?

The reasons are:

① There are too many materials

Within a single package, materials with different coefficients of thermal expansion (CTE) coexist, such as:

・Si chips

・Cu wiring

・Solder

・Resin

・Substrates

→ Stress inevitably occurs with temperature changes.

② Higher heat density

In AI chips and HBM:

・Local temperatures are very high

・Temperature gradients are large

→ Stress concentration and cracks occur easily.

③ Fine, high-density structures

・Bumps are small

・RDL is thin

・TSVs increase

→ Even slight deformation leads directly to failure.

(1) Thermal Cycling Test

・Repeats low temperature ↔ high temperature

・Example: -40°C ↔ 125°C

Evaluates:

・Solder fatigue

・Cracks

・Delamination

The most basic and most important test.

(2) High Temperature Operating Life Test (HTOL)

・Voltage is applied continuously at high temperature

・Operated for a long time

Evaluates:

・Wiring degradation

・Dielectric breakdown

・Electrical drift

(3) Drop and Shock Tests

・Important for smartphone applications

・Evaluates mechanical strength after mounting

Evaluates:

・Bump cracks

・Chip cracks

・Substrate cracks

(4) Temperature-Humidity Tests (HAST / THB)

・Evaluates resistance in high-temperature, high-humidity environments

Evaluates:

・Corrosion

・Ion migration

・Resin degradation

Solder Fatigue

・Repeated deformation due to temperature cycling

・Cracks eventually occur

Delamination

・Separation at material interfaces

・Increased thermal resistance → further degradation

Bump / RDL Cracks

・The allowable amount of deformation decreases with scaling

・Pronounced in fan-out

Chip Cracks

・Reduced thickness (thin die)

・Caused by stress concentration

For automotive (AEC-Q100), the requirements are on a different level.

Characteristics:

・Service life: 10–15 years or more

・Temperature range: -40 to 150°C or more

・Frequent vibration and shock

・Failure = risk to human life

For this reason:

・Material selection is the top priority

・Test conditions that may seem excessive

・Margin design is essential

A design that does not fail is itself what creates competitiveness.

Underfill Design

・Stress distribution

・Longer solder life

Low-Modulus Materials

・Stress relaxation

・Crack suppression

Package Structure Optimization

・Bump placement

・Chip thickness

・RDL layer structure

Use of Simulation

・Thermal analysis

・Stress analysis

・Lifetime prediction

・Simultaneous optimization of reliability × design (co-design)

・Combining physical testing with simulation

・AI-based lifetime prediction

・Redefining reliability metrics for HBM and chiplets

・Integrated thermal, electrical, and mechanical evaluation

・Package reliability is as important as performance

・Material differences, heat, and scaling make reliability difficult

・Thermal cycling is the most important test

・Automotive applications have requirements on a different level

・Comprehensive expertise in design, materials, and analysis is required

1.Why is ensuring reliability becoming more difficult in advanced packages?

2.Why is the thermal cycling test considered so important?

3.Why are reliability requirements especially strict for automotive applications?

 

Column Supervisor: Koji Kakumoto (President, OTIS Co., Ltd.)

After studying abroad and working in planning and development at a trading company, he joined OTIS Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as President, working to drive business growth and strengthen the organization.

 

This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.