A Presentation on

PRINTED CIRCUIT BOARD ASSEMBLY

1KIRAN HANJAR

Aim of the Presentation• Understanding PCB assembly using simulation with

DOE approach

• To assess the feasibility of process flow logic and

relative impact of changing line configurations

• It is aimed to identify constraints or bottlenecks and

development of improvement strategies accordingly

• By using DOE, the factors that are affecting the

system’s efficiency are identified

• Finally to improve the system’s overall performance 2

IntroductionPrinted circuit board (PCB) assembly•Printed circuit board (PCB) assembly lines fall under the general category of serial production lines•Common problems faced in these lines include designing configuration of existing or future lines to meet target production rates•Simulation modeling can capture the complex behaviour and interaction between various components of PCB assembly lines•This is very much important to analyze and help to make better decisions

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IntroductionPrinted Circuit Board Manufacturing•PCB can be classified into two categories based on the type of components placed on the board

– Surface Mount Technology (SMT)– Insertion Mount Technology (IMT)

Six steps involved in SMT manufacturing are explained as follows:• Attachment Media Dispensing•Component Placement•Curing•Soldering•Cleaning•Testing

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SOLDER PASTE APPLICATION

INVERT BOARD

CLEANPASS?

COMPONENT PLACEMENT

REFLOW OVEN

YESOTHER SIDE NEEDED SMC’s

TEST

SHIPREPAIR

NO

YES

NO

FINISHED BOARD

General steps involved in SMT process for PCB assembly

Source: (Hollomon, 1989) and (Capillo,

1990)

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MATERIALS

Components

Board

Paste Type

THROUGHPUT

Rework

Handling

Setup

PERSONNEL

Screen Printing

Component Placing

MACHINE

Board Functional Testing

In-Circuit Testing

TESTING

Cause and Effect Diagram for PCB assembly line

With the help of Cause and Effect Diagram factors which are affecting throughput are identified

Generally in PCBA solder paste, Component placement, ICT, BFT , Rework creates variability in process time

DOE• Systematic Plan of investigation using principles of statistics

wherein response or output value is obtained by varying factors/ levels or a combination of factor level

• 5 factors , 2 levels (high and low) are considered , 25 full factorial design is made to anlayse the model

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PARAMETERS FACTOR LEVEL ( LOW )

FACTOR LEVEL (HIGH)

SOLDER PASTE 5 7COMPONENT PLACING 7 12

ICT 5 15BFT 15 40

REPAIR 5 20

C.V for low level and high level are 0.1 and 0.4 respectively

Simulation Modeling and Analysis

The steps involved in a simulation •Input analysis: involves collection and analysis of data, and definition as well as validation of conceptual model•Model development: involves simulation model development followed by verification and validation of the simulation model•Output analysis: where performance metrics of the system are determined and analysed

Some of the advantages of simulation are: •Simulation offers better control over experimental conditions •Animation provided by simulation enables better understanding of the system •Alternative proposed system configurations can be compared using simulation

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Model BuildingIt involves six steps as shown in the figure

Collect i/p data

Develop static model

Validate simulation

model

Run current configuration

Analyse the system

Modify configuratio

n

Stop

Potential improvements

Yes

No

Source :(Mukkamala, Smith & Valenzuela, 2003) 9

Step 1 : Collect input data

This data may be extracted from historical databases of the line under consideration (if the manufacturing line already exists) or a similar line (if line is non-existent, i.e. proposed).•Machine Data•Operator data•Inspection and rework data•Oven data•Buffer data•Conveyor data•Traverser/shuttle data For a PCB that has to get shipped it has to start from Solder paste assembly then to component placement, Reflow oven, Pin through holes, Wave soldering, In-circuit testing, Final mechanical assembly, Board functional testing, Repair if any and finally to packing. 10

Solder paste Assembly

Wave Soldering

PTH

CoolingReflow Oven

Component placing

YesFinal Mechanical assembly

BFT

Disassemble

Rework

Ship

ICT

Repair

No

No

Yes

The simulation model of Printed Board Circuit Assembly

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Process carried out in each Section

Solder Paste Assembly•In PCBA the paste printing process accounts for the majority of assembly defects•Over sixty percent of all soldering defects are due to problems associated with the screening process•Parameters such as squeegee pressure, squeegee speed, stencil separation speed, snap-off and stencil cleaning interval are the most important factors in the process to achieve a better yield •The set up time taken is around five to seven minutes, two minutes is required to paste on stencil to get completed, Board printing takes one minute and visual inspection takes around two minutes and vary depending on the complexity of the board• So the time taken for the entire process is around six minutes

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Component Placing• In the pick & place station, only one components is

taken from the component feeder by means of a vacuum pipette, and is placed on the PCB

• Based on the complexity of the PCB the process time varies between seven and twelve minutes

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Reflow oven• A reflow oven is a machine used primarily for reflow

soldering of surface mount electronic components to printed circuit boards

• The oven contains multiple zones, which can be individually controlled for temperature

• The PCB moves through the oven on a conveyor and is therefore subjected to a controlled time-temperature profile

• Some ovens are designed to reflow PCBs in an oxygen-free atmosphere. Nitrogen (N2) is a common gas used for this purpose. This minimizes oxidation of the surfaces to be soldered

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In-Circuit Test (ICT)

• Here, checking for shorts, opens, resistance, capacitance, and other basic quantities which will show whether the assembly was correctly fabricated

• It may be performed with a bed of nails type test fixture and specialist test equipment

• Based on the design of the circuit and complexity it takes around five to fifteen minutes to undergo this process

Industrial printed circuit board being tested with a modern digital oscilloscope an

oscilloscope15

Board Functional Test (BFT)• Functional test (FCT) is used as a final manufacturing step

providing a pass/fail determination on finished PCBs before they are shipped

• To validate that product hardware is free of defects that could, otherwise, adversely affect the product’s correct functioning in a system application

• Requirements of a functional test, its development, and procedures vary widely from PCB to PCB and system to system

• The most common form of functional test, known as “hot mock-up” simply verifies that the PCB is functioning properly

• Generally time taken to undergo functional test is between fifteen and forty minutes

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Step 2 : Develop Static Model of the Process Line

• Based on the input data collected, a static model is prepared for the validation and benchmarking of the simulation model

• Static model is a spreadsheet based model developed using the mean values of cycle times, utilization time and failure

• Then, the throughput which is the least among all the machines or processes is identified as the throughput of the whole line

In doing so, these things are should be ignored: • The inherent interdependence between the processes

(induced by the capacitated buffers). • The variability (induced by the unpredictable breakdowns

and component part exhaustions)

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Input DatasheetSl no Process Time distribution in min

1 Solder paste assembly NORM (6. 1.2)

2 Component placement BETA (12, 7)

3 Reflow oven NORM ( 4, 0.1)

4 Cooling NORM (1, .05)

5 Pin through hole NORM ( 4 , 0.5)

6 Wave Soldering NORM ( 3.5, 0.5)

7 ICT BETA ( 15, 5)

8 Repair(ICT) BETA ( 20, 5)

9 Final mechanical assembly NORM ( 4, 0.5)

10 BFT BETA ( 40, 15)

11 Disassemble NORM ( 2, .05)

12 Rework (BFT) BETA (20, 5)

By using Arena software PCB Assembly line is built and respected inputs are tabulated at every section and Run simulation. From the result obtained analysis is done

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Run Current Configuration

Arri v e

Arriv e 1

Serv e r

Serv er 1Serv e r

Serv er 2Serv e r

Serv er 3Serv e r

Serv er 4

Serv e r

Serv er 5

Serv e r

Serv er 6

Serv e r

Serv er 7

In s p e c t

Inspec t 1

Serv e r

Serv er 8

Serv e r

Serv er 9

In s p e c t

Inspec t 2

Dep a rt

Depart 1

Serv e r

Serv er 10

PCb as sembly500

Sim u la te

? ?

19It took 252 min to complete the assembly process for a batch of 10 PCB

Analysing the variability using DOE • To understand the behaviour of the system to a next level the

factors (process) that are creating the variables are identified• For the current model five factors are taken into account they are:

– Solder paste assembly– Component Placing– ICT– BFT and– Rework

• By taking low level and high level concentration 25 factorial design is made

• To eliminate the bias randomization is done as shown in the following table

• In the table below : A- Solder paste assembly process time, B- component Placement process time, C – ICT Processing time, D- BFT Processing time, E- time taken to repair, I- process time taken for ten batches. 20

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The simulation model is run accordingly to the random number assigned to the order number and the obtained results are analysed using MINITAB software

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From the Main Effects plot for Time , Factor D i.e., Board Functional Test is one which is causing delay in process time than the other factors

Main Effects Plots

Estimated Effects and Coefficients for TIME(min) (coded units)

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Analysis of Variance for TIME(min) (coded units)

• From the Main effects plots and ANOVA table it is found that BFT plays a significant role in process. Simulation showed that the Bottleneck created in this section and there were queue of PCB that has to wait.

• In order to improve the system it is better to provide a one more BFT section (parallel).

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Source DF Seq SS Adj SS Adj MS F PMain Effects 5 688160 688160 137632 * *2-Way Interactions 10 2496 2496 250 * *3-Way Interactions 10 746 746 75 * *4-Way Interactions 5 187 187 37 * *5-Way Interactions 1 55 55 55 * *Residual Error 0 * * *Total 31 691644

Conclusion • These topics help us to know the problem of simulation modeling and

analysis of PCB assembly lines • This is an important problem as line managers and decision makers of PCB

assembly lines often face situations like designing configuration of entire line for new product etc, by using simulation concepts and software one can take a quantitative decisions but it is left to the line managers ability and experience to take the qualitative decisions

• By the help of Simulation one can understand visualise some more things such as buffer, bottleneck etc.

• By using Design of experiments, the factors that are affecting the model flow and also provide valid information whether to add a new line in the production to meet the demand or remove the parallel lines if the demands are not so good, without affecting the actual flow line.

• As in this case it clearly stated there is need for adding another line for BFT section in order to avoid blocking, bottlenecks etc.

• Hence with help of quantitative results and qualitative aspects optimal solution for any kind of problems can be found out

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References• Law, A. M. and Kelton, D. W. (2000). Simulation Modeling and Analysis. McGraw-Hill Companies, Inc.• Papadopoulos, H.T. and Heavy, C. (1996). Queuing theory in manufacturing systems analysis and design: a

classification of models of production and transfer lines. European Journal of Operations Research,92, 1-27.• Heavy, C., Papadopoulos, H.T., and Browne, J. (1993). The throughput rate of multistation unreliable production

lines.European Journal of Operational Research68(1), 69-89.• Hollomon, James K. Jr. (1989). Surface mount technology for PC board design.Indianapolis: Howard W. Sams &

Company.• Goss, G.B. (2000). Measuring machine interference to evaluate an operator cross-training program. M.S. thesis.

Massachusetts, MA: Massachusetts Institute of Technology.• D’Souza, R.C. (2004) A throughput-based technique for identifying production system bottlenecks. M.S. thesis.

Mississippi, MI: Mississippi State University.• Capillo, C. (1990). Surface Mount Technology: materials, processes, and equipment. McGraw-Hill Publishing

Company.• Kamath, M. (1999). Recent development in modeling and performance analysis tools for manufacturing systems. In:

S. B. Joshi and J. S. Smith, Computer Control of Flexible Manufacturing Systems, (pp.231-263). Chapman and Hall.• Law, A.M. and McComas, M.G. (1997). Simulation of manufacturing systems. Proc. of 1997 Winter Simulation Conf.,

86-89• Kotcher, R.C. (2001). How “overstaffing” atbottleneck machines can unleash extra capacity. Proc. of the 2001 Winter

Simulation Conference, 1163-1169.• Conway, R., Maxwell, M., McClain, J.O., and Thomas, J.L. (1988). The role of work-in process inventory in serial

production lines. Operations Research,36(2), 229-241.• Simulation modeling and analysis of printed circuit board assembly lines: Pradip Dinkarrao Jadhav• Design and Analysis of Experiments. 5th edition, Douglas C.Montgomery, Wiley student edition .

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Thank you

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Kiran Hanjar S1MS12MIA03

II Sem, IE M.TECHMSRIT