M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability What is Design for Reliability, Microsystems Failure & Failure Mechanisms, Fundamental of Design for Reliability, Thermomechanically- Induced Failure, Electrical Induced Failure and Chemical Induced Failure.

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Every electronic product is designed to meet four criteria. Performance Cost Size Reliability Electrical designers typically design for performance and size. Manufacturing engineers typically design for cost. Reliability? Reliability – is defined as the probability that a system will function within acceptable limits for a given period of time.

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Reliability When a product performs as designed, it is said to be reliable; when it does not, it is unreliable. Long term reliability? - personal computer = 5-7 years - electronic component = over 30 years - automotive controller = years To ensure that the electronics systems packaging will be reliable over an extended period of time, two approaches need to be followed: 1.Design for Reliability 2.Reliability testing

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Design for Reliability Design the systems packaging up-front for reliability -Predetermine various potential failure mechanisms that could result in product failure. -Create designs and select materials and process that would minimize or eliminate the chances for the failures. -Design for reliability aims to understands, identify and prevent such underlying failures even before the packages are built.

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Reliability Testing Conduct an accelerated test on the systems packaging for reliability -After a system is built and assembled, the system is subjected to accelerated test conditions. -Test conditions thermal cycling temperature and humidity cycling power cycling for short periods of time (by applying higher temperature, higher humidity, higher voltage, higher pressure and more to accelerate the failures process)

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Reliability Metrology -Refers to the measurement and mathematical modeling of reliability and patterns of failure. -It uses the mathematical tools of probability and statistical distributions to effectively collect, classify and process the test data to understand the patterns of failure and to identify the potential of failure.

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Microsystems Failures and Failure Mechanisms Failure mechanisms occur at the lowest hardware level, the effect are often at system level. Example: - A computer may not boot up when powered up. - TV may not show any picture when turned on. High – level symptoms, cause can be cracking of a chip due to thermally-induced stress or an electrical opening of an interconnect due to corrosion or a shorting of a circuit due to moisture or electrostatic discharge. - Whatever cause or failure mechanisms, the result is that the system is not reliable or usable.

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Microsystems Failures and Failure Mechanisms

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Microsystems Failures and Failure Mechanisms As seen in Figure: failure mechanisms can be classified into two mechanisms: - overstress mechanisms - wearout mechanisms Overstress mechanisms: - Is one in which the stress, in a single event, exceeds the strength or the cavity of the component and causes system failure. Wearout mechanisms: - Is gradual and occurs even at lower stress levels. - repeated application of lower stress over an extended period of time results in cumulative damage that makes the component eventually fail/ makes the system fail.

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Microsystems Failures and Failure Mechanisms We need to understand the various failure mechanisms (overstress or wear out) in order to design against them We can design against failure by 1. Reducing the stresses that cause failure 2. Increasing the strength of the component This involves 1.Selecting alternate materials 2.Changing the package geometry and dimensions. 3.Introducing new protection or encapsulation 4.Combination of these methods

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Microsystems Failures and Failure Mechanisms Definition Strain is defined as the increase in length per unit length of a body subjected to an applied stress. Stress is defined as the applied force per unit area of cross-section of a body.

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Microsystems Failures and Failure Mechanisms Typical failure mechanisms in semiconductor packaging are categorized into few levels – Die level Substrate/board level Interconnect (between die-to -substrate and substrate-to- board) Assembly/package level

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Thermomechanically-Induced Failures These failures result from stresses and strain generated within electronic package by external or internal heating thermal loading of the system due to: 1.Mismatch of the thermal coefficient of expansion of the different materials 2.Thermal gradients in the system 3.Geometric constraints

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Thermomechanically-Induced Failures

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Thermomechanically-Induced Failures Figure beside illustrate the shear strain point, wherein the max strain is at the outside-edge solder ball where the distance from neutral points (DNP) is maximum.

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability The Various Thermomechanical Failure Mechanisms 1.Fatigue Crack 2.Brittle facture - is a fracture that occurs rapidly (overstress failure mechanism), with little or no warning when the induced stress exceeds the fracture strength of the material 3.Creep 4.Interfacial delamination 5.Plastic deformation

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability The Various Thermomechanical Failure Mechanisms

M.Nuzaihan DMT 243 – Chapter  m Crack length 100  m Crack length Cu PCB Cu PCB Cu Crack Crack Initiation The Various Thermomechanical Failure Mechanisms

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Electrically-Induced Failures All failures in electronic products are electrical failures. However we should carefully distinguish electrical failure that are mechanically-induced, electrically-induced or chemically- induced and eventually exhibit themselves as electrical failures. Electrically induced-failures. 1.Electrostatic discharge 2.Gate Oxide breakdown 3.Electromigration

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Electrically-Induced Failures 1.Electrostatic discharge (ESD) is the transfer of charge between two bodies at different potentials by direct contact or induced by an electrostatic (electromagnetic) field. 2.An electrical short between the gate metallization and the channel of a MOSFET destroys the operation of the device and is called gate oxide breakdown. 3.Electromigration is an atom flux induced in metal traces by high current densities.

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Figure depicts an SEM image of metal trace before and after electromigration has taken place. The ion flux generated due to the high current density has caused an electrical open in the circuit.

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Chemically-Induced Failures There are three chemically driven processes that can lead to cracking/failure of the package 1.Electrochemical reactions (corrosion) 2.Diffusion of material 3.Dendritic growth (saliran bentuk ranting ) The reactions are often aggravated by increased temperature, increased voltage and increased thermally

M.Nuzaihan DMT 243 – Chapter 5 Fundamental Design For Reliability Chemically-Induced Failures There are three chemically driven processes that can lead to cracking/failure of the package 1.Electrochemical reactions (corrosion) 2.Diffusion of material 3.Dendritic growth (saliran bentuk ranting ) The reactions are often aggravated by increased temperature, increased voltage and increased thermally