1. CHAPTER 6: IC ASSEMBLY, PACKAGING AND TESTING
DDE 3253 – MICROELECTRONICS prepared by Assoc Prof Dr. Salwani Mohd Daud
CHAPTER 6: IC ASSEMBLY, PACKAGING AND TESTING
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2. Assembly
The process of putting the integrated circuit inside a package to make it reliable and convenient to use is known as semiconductor package assembly, or simply 'assembly'. 
Over the years, the direction of assembly technology is to develop smaller, cheaper, more reliable, and more environment-friendly packages.
Just like wafer fabrication technology, assembly technology has advanced tremendously that there are now a multitude of packages to choose from.
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3. In general, an assembly process would consist of the following steps:
Assembly - cont
In general, an assembly process would consist of the following steps: 
1) die preparation/separation, which cuts the wafer into individual integrated circuits or dice; 
2) die attach, which attaches the die to the support structure (e.g., the leadframe) of the package;
3) wire bonding, which connects the circuit to the electrical extremities of the package, thereby allowing the circuit to be connected to the outside world; and
4) encapsulation (usually by plastic molding), which provides 'body' to the package of the circuit for physical and chemical protection.
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4. Assembly - cont
Subsequent steps that give the package its final form and appearance vary from package to package.
Steps like marking and lead finish give the product its own identity, improve reliability, and add an extra shine.
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5. Assembly - cont
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6. Wafer backgrind
Wafer Backgrind is the process of grinding the backside of the wafer to the correct wafer thickness prior to assembly. 
It is also referred to as 'wafer thinning.'  
Wafer backgrinding has not always been necessary, but the drive to make packages thinner and thinner has made it indispensable.
Most package types in the semiconductor industry today would require a wafer thickness ranging from 8 mils to 20 mils.
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7. Die preparation/separation
Die preparation is the process by which the wafer is singulated into individual dice in preparation for assembly.  
Die preparation consists of two major steps, namely, wafer mounting and wafer saw.
Wafer mounting is the process of providing support to the wafer to facilitate the processing of the wafer from Wafer Saw through Die Attach.
During wafer mounting, the wafer and a wafer frame are simultaneously attached on a wafer or dicing tape.
The wafer frame may be made of plastic or metal, but it should be resistant to warping, bending, corrosion, and heat. 
The dicing tape (also referred to as a wafer film) is just a PVC sheet with synthetic adhesive on one side to hold both the wafer frame and the wafer.
Typically measuring 3 mils thick, it should be flexible yet tough and strong, and with low impurity levels as well.
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8. Die preparation/separation – cont.
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9. Die preparation/separation – cont.
Wafer saw follows wafer mounting and is the step that actually cuts the wafer into individual dice for assembly in IC packages. 
The wafer saw process consists of the following steps: 
1) the frame-mounted wafer is automatically aligned into position for cutting;
2) the wafer is then cut through its thickness according to the programmed die dimensions using a resin-bonded diamond wheel (rotating at a very high rpm;
3) the wafer goes through a cleaning process using high pressure water sprayed on the rotating workpiece and then dried by air-blowing.
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10. Common Failures of Die separation
       
Die Lifting - detachment of the die from the die pad or cavity. Wafer backside contamination during die preparation may inhibit good adhesion between the die backside and the die attach material. Other Common Causes of Die Lifting: contamination on the die pad or cavity, excessive die attach voids, incomplete die attach coverage, inadequate die attach curing      
Die Cracking - occurrence of fracture anywhere in the die.  Incorrect wafer saw and washing parameters can result in microcracks in the wafers, which can propagate into larger die cracks during later stages of the assembly process. Other Common Causes of Die Cracking: excessive die attach voids, die overhang or insufficient die attach coverage, excessive die ejection force on the wafer tape
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11. Common Failures of Die separation – cont.
Die Scratching - inducement of any mechanical damage on the die, as when an operator scratches a die with tweezers due to mishandling. Die scratches can also result from mishandling of wafers during the die preparation process. Other Common Causes of Die Scratching: insufficient operator training, disorderly workplace, use of improper tools
Die Metallization Smearing - depression or deformation of any metal line on the die surface. Common Causes: dirty or worn-out die attach pick-and-place tool, wafer mishandling
Die Corrosion - corrosion of the metallization and other components of the die. Common Causes: corrosive contaminants on the wafer tape or rinsing water   
Die Contamination - contamination of the die surface with silicon dust or foreign material that may be attached either by electrostatic, mechanical, or chemical means. Common Causes: contaminated rinsing water; static charge
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12. Die Attach
Die Attach (also known as Die Mount or Die Bond) is the process of attaching the silicon chip to the die pad or die cavity of the support structure (e.g., the leadframe) of the semiconductor package.
There are two common die attach processes, i.e., adhesive die attach and eutectic die attach.  Both of these processes use special die attach equipment and die attach tools to mount the die.
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13. Adhesive Die Attach
Adhesive die attach uses adhesives such as polyimide, epoxy and silver-filled glass as die attach material to mount the die on the die pad or cavity.
The adhesive is first dispensed in controlled amounts on the die pad or cavity.
The die for mounting is then ejected from the wafer by one or more ejector needles.
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14. Eutectic Die Attach
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15. Die Attach Failures
Die Lifting - detachment of the die from the die pad or cavity. Common Causes: contamination on the die pad or cavity, die backside contamination, excessive die attach voids, incomplete die attach coverage, inadequate die attach curing   
Die Cracking - occurrence of fracture anywhere in the die. Common Causes in the context of Die Attach: excessive die attach voids, die overhang or insufficient die attach coverage, insufficient bond line thickness, excessive die ejection force on the wafer tape, absence of die attach voids
Adhesive Shorting - electrical shorting between exposed metal lines, bond pads, bonds, or wires as a result of adhesive accidentally dripping on the surface of the die (sometimes called 'epoxy on die').  Common Causes: incorrect die attach material viscosity, incorrect adhesive dispensation
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16. Die Attach Failures –cont.
Bond Lifting - lifting of the first or second bond from the die or leadfinger, respectively. From the die attach process point of view, this is often due to resin bleeding of the die attach material into the bond pads or leadfingers, inhibiting good intermetallic formation. See also Wirebonding.
     
Die Scratching - inducement of any mechanical damage on the die, as when an operator scratches a die with tweezers due to mishandling. Common Causes: insufficient operator training, worn-out or contaminated pick-and-place tool, disorderly workplace, use of improper tools
    
Die Metallization Smearing - depression or deformation of any metal line on the die surface. Common Causes: dirty or worn-out die attach pick-and-place tool, wafer mishandling
Dec 06 - May 07

17. Three types of wire bonding
Wirebonding is the process of providing electrical connection between the silicon chip and the external leads of the semiconductor device using very fine bonding wires.
The wire used in wirebonding is usually made either of gold (Au) or aluminum (Al), although Cu wirebonding is starting to gain a foothold in the semiconductor manufacturing industry.
Three types of wire bonding
Thermocompression ball bonding
Ultrasonic ball bonding
Thermosonic ball bonding
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18. Thermocompression Ball Bonding
Figure Figure 2-102
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19. Ultrasonic Ball Bonding
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20. Ultrasonic Ball Bonding – cont.
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21. Thermosonic Ball Bonding
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22. Thermosonic Ball Bonding – cont.
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23. Ball Bonding
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24. Wire bonding technology comparison
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25. Wire Bonding Failures
Ball Bond Lifting - detachment of the ball bond from the silicon chip; also refers to non-sticking of the ball bond to the bond pad.
Common Causes: contamination on the bond pad, incorrect wirebond parameter settings, instability of the die during bonding, bond pad corrosion, excessive bond pad probing, Kirkendall voiding, intermetallic spiking due to the Devaney mechanism, excessive thermal stress resulting in excessive intermetallic formation, bond pad metallization/barrier metallization lifting, cratering.
Wedge Bond Lifting - detachment of the wedge bond from the silicon chip, bonding post, or leadfinger; non-sticking of the wedge bond to the bond pad, post, or leadfinger.
Common Causes: contamination on the bond pad or leadfinger, incorrect parameter settings, instability of the die or leadframe during bonding, bond pad or leadfinger corrosion, excessive bond pad probing         
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26. Wire Bonding Failures – cont.
Ball Bond Neck Break - breakage of the wire at the neck of the Au ball bond.
Common Causes: incorrect wirebond parameter settings, incorrect wire looping, die-to-package delamination, excessive wiresweeping during mold, excessive die overcoat, 'bamboo' grain structure due to excessive thermal treatment
Wedge Bond Heel Break - breakage of the wire at the heel of the Al wedge bond.
Common Causes: incorrect wirebond parameter settings, incorrect wire looping, leadfinger-to-package delamination, excessive wiresweeping during mold
   
Midspan Wire Break - breakage along the span of the wire.
Common Causes: wire nicks or damage, wire corrosion, tight wire looping, excessive wiresweeping, electrical overstress
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27. Molding/Encapsulation
Molding is the process of encapsulating the device in plastic material.
Transfer molding is one of the most widely used molding processes in the semiconductor industry because of its capability to mold small parts with complex features.
In this process, the molding compound is first preheated prior to its loading into the molding chamber.
After pre-heating, the molding compound is forced by a hydraulic plunger into the pot where it reaches melting temperature and becomes fluid.
The plunger then continues to force the fluid molding compound into the runners of the mold chase.
These runners serve as canals where the fluid molding compound travels until it reaches the cavities, which contain the leadframes for encapsulation
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28. Molding/Encapsulation – cont.
Plastic Dual In Line Package (PDIP)
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29. Transfer Molding Procedure
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30. CERDIP – Ceramic DIP
Assembly Sequence
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31. Final Test
Humidity Test – is an environmental test where the device is exposed to high humidity and temperatures (85% relative humidity and 85C) while having the IC power up. This test is designed to measure the device to the effects of corrosion.
Burn-In – is an electrical and thermal stress test designed to eliminate early failures. The IC’s are power up in a furnace to put the IC’s in a stress mode and cause failure.
Thermal Shock Test – place the devices into a hot environment and quickly move the device into a very cold environment.
Mechanical Shock Test – are performed on the ICs to determine if the devices can withstand a certain degree of shock.
Pressure Cooker Test – exposes the test device to an atmosphere of high temperature under a pressure of 2 atmosphere to determine the ability of the device to withstand galvanic corrosion due to the encapsulating materials used.
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32. Basic IC Manufacturing Process
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