reliability issues

Reliability Issues

Mohammad Sharifkhani

Reading

• Textbook I Chapter 18• Textbook I Chapter 20• The paper on SER

Motivation

• There is a long distance from a chip working in a lab to a chip working in the field

• Reliability• Robustness• Fatigue • Many of the culprits are in rise as technology

scales

Introduction

• Packaging• Electromigration• ESD Protection• SER Protection

Chip Packaging

ChipL

L ´

Bonding wire

Mountingcavity

Leadframe

Pin

•Bond wires (~25m) are used to connect the package to the chip

• Pads are arranged in a frame around the chip

• Pads are relatively large (~100m in 0.25m technology),with large pitch (100m)

•Many chips areas are ‘pad limited’

Pad FrameLayout Die Photo

Chip Packaging• An alternative is ‘flip-chip’:– Pads are distributed around the chip– The soldering balls are placed on pads– The chip is ‘flipped’ onto the package– Can have many more pads

Tristate Buffers

InEn

En

V DD

Out

Out = In.En + Z.En

V DD

In

En

EnOut

Increased output drive

Electromigration• Current density (current per unit area)• A reliability issue creates problem over time– Due to transport of metal ions– AC signals will be fine

• Breaking or shorting to adjacent wire• Keeping current below 0.5 to 1mA/um relaxes the

problem– For DC wires (power/GND)

• IR Drop transient problem (peak current)• Electromigration DC problem (ave. current)• Using copper helps

Electromigration (1)

Limits dc-current to 1 mA/m

Electromigration (2)

Electro-Static Discharge (ESD)


Which one fails?


Second breakdown of the path at a lower voltage than the second break-down of the ESD path

Second breakdown of the path at a higher voltage level than the second break-down of the ESD path


There are challenges as technology scales!


Design of ESD protection circuits:A glimpse!


• ESD protection is extremely important when dealing with high speed input output signals• I/O Capacitance

Soft Error

reliability issues

Documents

esd pathsecond breakdown

chip pads

chip working

padsthe chip

problemfor dc wires

unit areaa reliability

lower voltage

large pitch