ECEN5004 Ch5 Essay example

Submitted By Hemil-Varkhade
Words: 1977
Pages: 8

FUNDAMENTALS OF
DESIGN FOR RELIABILITY

Marko Bundalo
Adeel Baig

Chapter Objectives


Introduce the need for design for reliability



List the main causes of reliability failures



How do failures relate to their mechanisms



Describe each failure



Propose design guidelines against the failure
Microsystems Packaging

Introduction
Electronic Product:
• Performance
• Cost
• Size
• Reliability

Electrical:
• Performance
• Size

Manufacturing:
• Cost

Microsystems Packaging

• Reliability

Reliability


Often not designed up-front.



Tested during the product qualification or after the product is manufactured.



Expensive and time-consuming approach.



Design for RELIABILITY as well !!!
Microsystems Packaging

5.1 What is Design for Reliability


Product performs the functions – reliable product



“Long-term” reliability (i.e. Automobile, Personal Computer)



Economically not viable to test “long-term” reliable products for several years before they are sold out.



To ensure over an extended period of time, two approaches can be taken: Design the systems packaging up-front for reliability.

1.
2.

Conduct an accelerated test on the systems packaging for reliability after the system is designed, fabricated & assembled.

Microsystems Packaging

1. Design the systems packaging up-front for reliability


Predetermine various potential failure mechanisms 

Create and select materials and processes – minimize/eliminate the chances for the failures



“up-front” design



Design for reliability
Microsystems Packaging

2. Conduct an accelerated test on the systems packaging for reliability after the system is designed, fabricated & assembled


After a system is built and assembled, system accelerated to test conditions.



Temperature



Testing for reliability – Chapter 22

,humidity

,voltage ,pressure

Microsystems Packaging

Comparison and usage


Industrial practice uses Testing for Reliability



If {problems = TRUE}
Then (IC & system-level packages):
RE[designed, fabricated, assembled, tested]



Expensive and time consuming



Design for Reliability = Solution
Microsystems Packaging

5.2 Microsystems Failures and Failure Mechanisms


High-level symptoms (i.e. computer, TV)



Underlying cause (i.e. chip, corrosion, moisture, electrostatic discharge) – PRODUCT NOT RELIABLE



Design for Reliability understands, identifies, and prevents such failures
 Overstress

Mechanisms – stress exceeds the strength or capacity of the component and causes the system failure. (single event)

 Wearout

Mechanisms – gradual and occurs even at lower stress level. (repeated event)
Microsystems Packaging

Failure mechanisms is microelectronic system packages

Microsystems Packaging

5.3 Fundamentals of Design for Reliability


Important to understand the failure (why, where, how long, application, etc.)



Two methods for design against failure:

1.
2.

By reducing the stress that cause the failure.
By increasing the strength of the component.



Either one can be achieved by:





Selecting materials
Changing the package geometry
Changing the dimensions
Protection

Microsystems Packaging

5.4.1 What are Thermomechanically-induced Failures ?
- Caused by stresses and strains generated within electrical package due to thermal loading.
- Due to CTE (coefficient of thermal expansion), thermally-induced stresses are generated in various parts of system.
- Figure - Illustration of thermo mechanical deformation in solder joints
- αb BOARD
-

αc

COMPONENT

Microsystems Packaging



Tmax

chip carrier αc(Tmax – T0) per unit length board αb(Tmax – T0) per unit length

- Difference between the two expansions = net shearing displacement:
L(αb - αc)(Tmax – T0) where L – distance (of the solder joint) from the neutral point (DNP)


Tmin

chip carrier αc (Tmin – T0) per unit length board αb(Tmin – T0) per unit length

- Net shearing displacement:
L(αb - αc)(Tmin – T0)
- Difference in the displacement…