Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Integrated Circuits...

Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart

Integrated Circuits Cycle Time at Test Integrated Circuits Cycle Time at Test Operation EstimationOperation Estimation

for Production Planningfor Production Planningusing Computer Simulationusing Computer Simulation

ByBy

Jitrayut JunnapartJitrayut Junnapart


IntroductionIntroduction


Introduction(1): Introduction(1): Assembly ProcessAssembly Process

• General Process of IC manufacturing:General Process of IC manufacturing:


Introduction(2): Introduction(2): Electrical Test ProcessElectrical Test Process

• All products must be 100% tested before All products must be 100% tested before deliver to customersdeliver to customers

• Electrical Test process is shown below:Electrical Test process is shown below:


Introduction(3): Introduction(3): Electrical TElectrical Test Timeest Time

• TestTest Time depends on 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


Introduction(4): Introduction(4): An ExampleAn Example

• Suppose one production lot of:Suppose one production lot of:– 3,000 units3,000 units– Main Flow Test Rate Main Flow Test Rate = 1,000 UPH (Units Per Hour)= 1,000 UPH (Units Per Hour)– Rescreen Flow Test Rate Rescreen Flow Test Rate = = 300 300 UPH UPH – First Pass Yield First Pass Yield = 90%= 90%

• Calculate Cycle Time:Calculate Cycle Time: Main Flow Test TimeMain Flow Test Time = 3,000 / 1,000 = 3,000 / 1,000

= 3 hours= 3 hoursRescreen Flow Test TimeRescreen Flow Test Time = [ 3,000 * (1 - 0.9) ] / = [ 3,000 * (1 - 0.9) ] / 300300

= = 11 hour hour Total Test TimeTotal Test Time = 3 hours += 3 hours + 1 hour1 hour

= = 44 hours hours


Introduction(5): Why interesting?Introduction(5): Why interesting?• Electrical test time is very important becaElectrical test time is very important beca

use it use it dominates overalldominates overall IC manufacturin IC manufacturing cycle timeg cycle time

• There are methods to calculate cycle timeThere are methods to calculate cycle time::– Use average values (of UPHUse average values (of UPHss, FPY), FPY)– Apply simulation methodApply simulation method– OthersOthers


Literature ReviewLiterature Review


Literature Review(1)Literature Review(1)

• This project applies Monte Carlo This project applies Monte Carlo Simulation based on Simulation based on historical datahistorical data of:of:– Main flow test rate Main flow test rate – Rescreen flow test rateRescreen flow test rate– First pass yieldFirst pass yield

to simulate for total cycle time of one to simulate for total cycle time of one production lotproduction lot



• Monte Carlo simulation uses Monte Carlo simulation uses random random numbernumber to “pick” one value of data a to “pick” one value of data as a representative s a representative forfor further calculati further calculationon


Literature Review(3): ExampleLiterature Review(3): Example• Suppose we want to simulate main flow Suppose we want to simulate main flow

test timetest time

• And And partial of partial of historical data of main flohistorical data of main flow test time (in UPH)w test time (in UPH) looks like looks like::

100 130 150 160

140 120 160 110

120 150 100 160

160 130 110 140

110 150 170 150


Literature Review(4): Step 1Literature Review(4): Step 1

• Rearrange the numbers into frequency Rearrange the numbers into frequency and probability table:and probability table:

UPH Frequency Probability

100 1 0.0122

110 3 0.0366

120 3 0.0366

130 5 0.0610

140 7 0.0854

150 11 0.1341

160 14 0.1707

170 20 0.2439

180 18 0.2195

Total = 82



• Construct cumulative probability table Construct cumulative probability table from probability table:from probability table:

UPH Frequency Cum. Prob.

100 1 0.0122

110 3 0.0488

120 3 0.0854

130 5 0.1463

140 7 0.2317

150 11 0.3659

160 14 0.5366

170 20 0.7805

180 18 1.0000



• Set up probability intervals for ranges Set up probability intervals for ranges of UPH:of UPH:

UPH Probability Range

100 0.0000 - 0.0122

110 0.0123 - 0.0366

120 0.0367 - 0.0854

130 0.0855 - 0.1463

140 0.1464 - 0.2317

150 0.2318 - 0.3659

160 0.3660 - 0.5366

170 0.5367 - 0.7805

180 0.7806 - 1.0000



• Generate a random number and map Generate a random number and map onto the appropriate interval to find a onto the appropriate interval to find a simulated value of main flow UPHsimulated value of main flow UPH

UPH Probability Range

100 0.0000 - 0.0122

110 0.0123 - 0.0366

120 0.0367 - 0.0854

130 0.0855 - 0.1463

140 0.1464 - 0.2317

150 0.2318 - 0.3659

160 0.3660 - 0.5366

170 0.5367 - 0.7805

180 0.7806 - 1.0000

Random No.generated is

0.5934

Simulated UPH= 160



• Repeat step 1-Repeat step 1-44 but for: but for:– First Pass Yield and First Pass Yield and – Rescreen Flow UPHRescreen Flow UPH

• Use equation in Use equation in slide 5slide 5 to calculate to calculate SSimulated imulated TTotal otal TTest est TTimeime



• BUTBUT r realeal test rate (UPH) test rate (UPH) data is contidata is continuous numbernuous number (appendix C,p79) (appendix C,p79)

• We need to We need to groupgroup them first into rang them first into rangeses

• Then Then countcount number of data that are in number of data that are in each rangeeach range

• And find the And find the center valuecenter value of the grou of the group as a representative numberp as a representative number of the of the groupgroup



• Number of group can be chosenNumber of group can be chosen• GroupsGroups shall shall cover every datacover every data

–See appendix D, p.86 for detail


Project DevelopmentProject Development


Project Development (1)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


Project Development (Project Development (22))• 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.


Project Development (Project Development (33))• Scope and limitations of the projectScope 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 facility’s 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.


Project Development (Project Development (44))• Project Time Line:Project Time Line:

– The project consists of 9 major tasks– Total time taken is 7.5 months


Project Development (Project Development (55))• Feasibility StudyFeasibility 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


Project ImplementationProject Implementation


Project Implementation (1)Project Implementation (1)

1)1) Output must be easy for user to understandOutput must be easy for user to understand2)2) Test time depends on lot size, and it is not Test time depends on lot size, and it is not

feasible to provide all lot sizes outputfeasible to provide all lot sizes output3)3) User should have control over some User should have control over some

essential simulation parametersessential simulation parameters4)4) Change in source code is undesirableChange in source code is undesirable

• ConcernsConcerns

Need modificationsNeed modifications

1,2

3

4



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



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


Project Implementation (Project Implementation (44))• 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


Project Implementation (Project Implementation (55)): Files: Files

• Main flow UPH fileicname.mnf

• Rescreen flow UPH file

icname.rsf

• First pass yield file

icname.rrf

• Parameters file – para.txt

567.0652174580.6871609547.6097561594.5454545514.270073503.5632184554.0727273554.9477352

415.5066079309.3377483415.5066079452.0338983392.7272727368.125

376.8181818385.9550562

70.5194556370.9828101659.5136290875.2866972582.2226953483.7023510686.0011813381.10755321

1555

100010010.511

fh368fa

• List of icname file – progname.txt


Project Implementation (Project Implementation (66))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 divisions4. Calculate for accumulated probability5. Repeat step 1-4 but for rescreen rate and UPH of rescreen flow

1.Simulate total time used to test the production lot2.Count for number of success that the time used is less than allocated time3. Repeat 1 and 2 and calculate success probability 4.Record result in output file5.Increase allocated time

Allocated time > limit?

End

Yes

No

No Yes

Simulation MethodSimulation Method


Project Implementation (Project Implementation (77))

• 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


Simulation ResultSimulation Result


Simulation ResultSimulation Result ( (11))

• PC based result:1) Screen output


• PC based result:2) File output (result.txt)



• Unix

Based

result Control parameters inputPrinted out for monitoring

Compiledprogram

Screenoutput



• Unix

Based

result

Output fileGenerated



• Unix

Based

result

bkkeis{pemg}34: vi result.txt



Project EvaluationProject Evaluation


Project EvaluationProject Evaluation (1) (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


Project EvaluationProject Evaluation (2) (2)

– The simulated result is verified back to historical data

Times (Hrs) Success Total lots % Success (real data) % Success (simulated)2.00 22 66 33.33 302.50 56 66 84.85 813.00 64 66 96.97 92

– The result is 3-5% deviation – This is very good for simulation (proba

bilistic work)

• Verification of Result:


ConclusionsConclusions• Simulation technique can generate result that giSimulation technique can generate result that gi

ves adequate accuracy (3-5% error in this work)ves adequate accuracy (3-5% error in this work). The result can be transform in the way that it is . The result can be transform in the way that it is easy to understand by end user. easy to understand by end user.

• The planner (user) can assign allowable time The planner (user) can assign allowable time to to test production lot based on his/her confidence test production lot based on his/her confidence level that the lot will finish in timelevel that the lot will finish in time

• In this particular work, essential parameters in In this particular work, essential parameters in simulation can be changed easily in control files simulation can be changed easily in control files without modification to the main programwithout modification to the main program


Random Number GenerationRandom Number Generation• Confirm the even distribution by JMP

1,000 numbers 10,000 numbers

Cycle Time at IC Electrical Test Operation Simulation by Jitrayut Junnapart Integrated Circuits...

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