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
