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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Integrated Circuits Cycle Time at Test Operation Estimation for Production Planning using Computer Simulation By Jitrayut Junnapart

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Introduction

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Introduction(1): Assembly Process General Process of IC manufacturing:General Process of IC manufacturing:

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Introduction(2): Electrical Test Process All products must be 100% tested before deliver to customersAll products must be 100% tested before deliver to customers Electrical Test process is shown below:Electrical Test process is shown below:

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Introduction(3): Electrical Test Time Test Time depends on:Test Time depends on: –Test Rate at main flow (in Units Per Hour) –First Pass Yield (0 to 1 for 0% to 100%) –Test Rate at rescreen flow (in UPH) To P.15

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Introduction(4): An Example Suppose one production lot of:Suppose one production lot of: –3,000 units –Main Flow Test Rate = 1,000 UPH (Units Per Hour) –Rescreen Flow Test Rate = 300 UPH –First Pass Yield = 90% Calculate Cycle Time:Calculate Cycle Time: Main Flow Test Time= 3,000 / 1,000 Main Flow Test Time= 3,000 / 1,000 = 3 hours Rescreen Flow Test Time= [ 3,000 * (1 - 0.9) ] / 300 = 1 hour Total Test Time= 3 hours + 1 hour Total Test Time= 3 hours + 1 hour = 4 hours

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Introduction(5): Why interesting? Electrical test time is very important because it dominates overall IC manufacturing cycle timeElectrical test time is very important because it dominates overall IC manufacturing cycle time There are methods to calculate cycle time:There are methods to calculate cycle time: –Use average values (of UPHs, FPY) –Apply simulation method –Others

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Literature Review

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Literature Review(1) This project applies Monte Carlo Simulation based on historical data of:This project applies Monte Carlo Simulation based on historical data of: –Main flow test rate –Rescreen flow test rate –First pass yield to simulate for total cycle time of one production lot to simulate for total cycle time of one production lot

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Literature Review(2) Monte Carlo simulation uses random number to pick one value of data as a representative for further calculationMonte Carlo simulation uses random number to pick one value of data as a representative for further calculation

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Literature Review(3): Example Suppose we want to simulate main flow test timeSuppose we want to simulate main flow test time And partial of historical data of main flow test time (in UPH) looks like:And partial of historical data of main flow test time (in UPH) looks like:

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Literature Review(4): Step 1 Rearrange the numbers into frequency and probability table:Rearrange the numbers into frequency and probability table:

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Literature Review(5): Step 2 Construct cumulative probability table from probability table:Construct cumulative probability table from probability table:

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Literature Review(6): Step 3 Set up probability intervals for ranges of UPH:Set up probability intervals for ranges of UPH:

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Literature Review(7): Step 4 Generate a random number and map onto the appropriate interval to find a simulated value of main flow UPHGenerate a random number and map onto the appropriate interval to find a simulated value of main flow UPH Random No. generated is 0.5934 Simulated UPH = 160

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Literature Review(8): Step 5 Repeat step 1-4 but for:Repeat step 1-4 but for: –First Pass Yield and –Rescreen Flow UPH Use equation in to calculate Simulated Total Test TimeUse equation in slide 5 to calculate Simulated Total Test Timeslide 5

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Literature Review(9) BUT real test rate (UPH) data is continuous number (appendix C,p79)BUT real test rate (UPH) data is continuous number (appendix C,p79) We need to group them first into rangesWe need to group them first into ranges Then count number of data that are in each rangeThen count number of data that are in each range And find the center value of the group as a representative number of the groupAnd find the center value of the group as a representative number of the group

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Literature Review(10) Number of group can be chosenNumber of group can be chosen Groups shall cover every dataGroups shall cover every data –See appendix D, p.86 for detail

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Development

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Development (1) Problem Definition:Problem Definition: –Electrical test time is the main dominator of overall production cycle time in back-end IC manufacturing –Cycle time affects shipping commitment to customers –Using average test time is not effective because the numbers vary over wide range Production control people wants a tool to forecast electrical test time of the IC

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Development (2) Objectives:Objectives: –To develop computer software that processes historical test rate data (in Units Per Hour - UPH) at main flow and rescreen flow, and first pass yield (retest rate-related) from production and simulate for probability to finish testing a production lot with various allocated time. –The computer software must be separated into main program and auxiliary data files. The main program will work with various environments without modification. –The developed simulation program code must work on both Personal Computer (PC) and larger computer running on UNIX operating system.

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Development (3) Scope and limitations of the project :Scope and limitations of the project : –It is considered that main flow test rate, rescreen flow test rate, and first pass yield being input of this project are available beforehand. They are stored in separated text files which, in fact, easy to develop the system further. –This project gives calculation output as a text file for easy to use in the future. Example of this is putting into Hypertext Markup Language (HTML) and post on facilitys Intranet. –The software in this project will calculate for success probability to finish electrical test process based on a certain size of production lot. User can later use linear relationship to calculate for other size.

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Development (4) Project Time Line:Project Time Line: –The project consists of 9 major tasks –Total time taken is 7.5 months

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Development (5) Feasibility Study :Feasibility Study : –Technical » Feasible The champion has knowledge of simulation and programming language –Economic » Feasible The project does not require special expenses –Operational » Feasible The project does not interfere the normal work practice of concerning people –Legal » Feasible Software used in development is legal and all data is legally used

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Implementation

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Implementation (1) 1)Output must be easy for user to understand 2)Test time depends on lot size, and it is not feasible to provide all lot sizes output 3)User should have control over some essential simulation parameters 4)Change in source code is undesirable ConcernsConcerns Need modifications 1,2 3 4

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Implementation (2) 1)An allocated time is set 2)The simulated test time for a certain lot size is calculated and compared to a allocated time. If test time is shorter than allocated time, the result is possible. This 'success number' is counted. 3)Repeat step 2 for many times and calculate success chance from success times and total simulation times and report this chance to user. 4)Increase the allocated time by delta defined 5)Repeat step 2 to 4 for certain rounds defined To solve concerns #1 and #2To solve concerns #1 and #2 To concerns

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Implementation (3) Store simulation parameters in file para.txt –Number of types of IC to perform simulation –Number of divisions to group historical data –Lot size that simulation is based on –Number of repetitive simulation for one allowable time –Start point of allowable time –Increment of allowable time –Steps of increment of allowable time To solve concerns #3To solve concerns #3 To concerns

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Implementation (4) To solve concerns #4To solve concerns #4 All input data are stored in separated files: 1)Historical files of Main flow UPH (.mnf) 2)Historical data of Rescreen flow UPH (.rsf) 3)Historical data of First pass yield (.rrf) 4)List of IC types file (progname.lst) To concerns

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Implementation (5): Files Main flow UPH file icname.mnf Rescreen flow UPH file icname.rsf First pass yield file icname.rrf Parameters file – para.txtList of icname file – progname.txt

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Implementation (6) Open file progname.lst and para.txt that stores test program names to simulate and read all the names and parameters Processed for every test program? 1.Open file that stores UPH Main flow, and read all main flow UPH for next program 2. Count number of data 3. Divide into divisions 4. Calculate for accumulated probability 5. Repeat step 1-4 but for rescreen rate and UPH of rescreen flow 1.Simulate total time used to test the production lot 2.Count for number of success that the time used is less than allocated time 3. Repeat 1 and 2 and calculate success probability 4.Record result in output file 5.Increase allocated time Allocated time > limit? End Yes No Yes Simulation Method

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Implementation (7) Programming –Coding is done in ANSI C language –Length of the program ~900 lines –Special statements and commands are avoided for the program can run both on PC and UNIX based computer system

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Simulation Result

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Simulation Result (1) PC based result: 1) Screen output

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart PC based result: 2) File output (result.txt) Simulation Result (2)

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Unix Based result Control parameters input Printed out for monitoring Compiled program Screen output Simulation Result (3)

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Unix Based result Output file Generated Simulation Result (4)

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Unix Based result bkkeis{pemg}34: vi result.txt Simulation Result (5)

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Evaluation

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Evaluation (1) Verification of Objectives : –Output is easy for non-engineering people to understand Yes –Control parameters used in simulation can be input to program through external file Yes –Various simulations can be performed without any changes to main program Yes –The source program can be compiled to work on both PC and UNIX based computer Yes

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Project Evaluation (2) –The simulated result is verified back to historical data –The result is 3-5% deviation –This is very good for simulation (probabilistic work) Verification of Result :

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Conclusions Simulation technique can generate result that gives adequate accuracy (3-5% error in this work). The result can be transform in the way that it is easy to understand by end user.Simulation technique can generate result that gives adequate accuracy (3-5% error in this work). The result can be transform in the way that it is easy to understand by end user. The planner (user) can assign allowable time to test production lot based on his/her confidence level that the lot will finish in timeThe planner (user) can assign allowable time to test production lot based on his/her confidence level that the lot will finish in time In this particular work, essential parameters in simulation can be changed easily in control files without modification to the main programIn this particular work, essential parameters in simulation can be changed easily in control files without modification to the main program

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Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Random Number Generation Confirm the even distribution by JMP 1,000 numbers10,000 numbers

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