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Chapter 7: Production of Printed Circuit Boards Focus on automated production of printed circuits by Surface Mounting Technology (SMT) and Hole Mounting Technology (HMT) The course material was developed in INSIGTH II, a project sponsored by the Leonardo da Vinci program of the European Union

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Chapter 7 production of printed circuit boards l.jpg
Chapter 7:Production of Printed Circuit Boards

  • Focus on automated production of printed circuits by Surface Mounting Technology (SMT) and Hole Mounting Technology (HMT)

The course material was developed in INSIGTH II, a project sponsored by the Leonardo da Vinci program of the European Union

Electronic Pack….. Chapter 7 Production of PCBs.


Hole mounting l.jpg
Hole Mounting

  • Axial components: Sequencing and mounting

  • Radial components: Mounting

  • DIP components: Mounting

  • Odd components: Robot or hand mounting

Fig. 7.1:The process for production of hole mounted PCBs

Electronic Pack….. Chapter 7 Production of PCBs.


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Hole Mounting, continued

Fig. 7.2 a): Schematic example of the most efficient sequence of mounting the components of a particular PCB.

Electronic Pack….. Chapter 7 Production of PCBs.


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Hole Mounting, continued

Fig. 7.2 b): The principle of sequencing.

Electronic Pack….. Chapter 7 Production of PCBs.


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Hole Mounting, continued

Fig. 7.3: Sequencing machine.

Electronic Pack….. Chapter 7 Production of PCBs.


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Hole Mounting, continued

Fig. 7.4: Axial inserter with two mounting heads.

Electronic Pack….. Chapter 7 Production of PCBs.


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Hole Mounting, continued

Fig. 7.5: Simplified process in the axial inserter:

1): Cutting the components from the tape

2): Lead bending

3) - 4): Insertion

5): Cut and clinch

6): Return to starting position.

Electronic Pack….. Chapter 7 Production of PCBs.


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Hole Mounting, continued

Fig. 7.6: DIP inserter.

Electronic Pack….. Chapter 7 Production of PCBs.


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Hole Mounting, continued

Fig. 7.7: Manual mounting board with light guide.

Electronic Pack….. Chapter 7 Production of PCBs.


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Hole Mounting, continued

Fig. 7.8: Wave soldering machine.

Electronic Pack….. Chapter 7 Production of PCBs.


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Wave Soldering, principle

  • Fluxing

  • Pre-heating

  • Soldering

  • (Cleaning)

    Fig. 7.9:

    a): Principle of foam fluxer.

    b): Control system for density and level of the flux bath.

Electronic Pack….. Chapter 7 Production of PCBs.


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Wave Soldering principle, continued

Fig. 7.10:a): Principle of wave soldering.

b): The real shape of the wave.

Electronic Pack….. Chapter 7 Production of PCBs.


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Wave Soldering, continued

Fig. 7.11:

a): Industrial in line cleaning machine.

b): The principle of ultrasound and vapour cleaning.

Electronic Pack….. Chapter 7 Production of PCBs.


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ElectroStatic Discharge (ESD) Precautions

Fig. 7.12: An ESD protected working space. The resistors R normally are 100 Kohm - 1 Mohm.

Electronic Pack….. Chapter 7 Production of PCBs.


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Surface Mounting

  • Soldering by wave solder process or by reflow processFig. 7.13: Application of adhesive for SMD mounting by:

    a): Screen printing

    b): Dispensing

    c): Pin transfer

Electronic Pack….. Chapter 7 Production of PCBs.


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Surface Mounting: Wave Solder Process

  • Apply adhesive by dispenser, screen printing or pin transfer

  • Cure by heat or UV

  • Turn board

  • Wave solder

    • Double-wave soldering machine common for SMT

    • Not all SMD components suitable for wave soldering

Electronic Pack….. Chapter 7 Production of PCBs.


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Surface Mounting, continued

Fig. 7.14: a): Shadowing in SMD wave soldering.

b): Solder bridging on fine pitch package.

Electronic Pack….. Chapter 7 Production of PCBs.


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Surface Mounting, continued

Lambda wave

Fig. 7.15: Double wave for SMD soldering. The first is a turbulent wave that wets, followed by a gentle “lambda wave” that removes superfluous solder.

Electronic Pack….. Chapter 7 Production of PCBs.


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Surface Mounting, continued

Fig. 7.16: Temperature profile during wave soldering in a double wave machine.

Electronic Pack….. Chapter 7 Production of PCBs.


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Reflow Solder Process

  • Print solder paste

  • Mount components

  • Dry solder paste

  • Solder by heating to melting of paste

Electronic Pack….. Chapter 7 Production of PCBs.


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Solder Paste

  • Consists of:

    • Solder particles (~ 80 % by weight)

    • Flux

    • Solvents and additives to give good printing properties (rheology)

  • Typical mesh count in screen: 80 per inch

  • Area ratio: Ao = a2 /(a+b)2

  • Paste volume deposited: V = Vo • Ao • t

  • "Solder ball test" for quality of solder paste and solder process

Electronic Pack….. Chapter 7 Production of PCBs.


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Solder Paste, continued

Fig. 7.17: Microphotograph of Multicore solder paste type Sn 62 RMA B 3. The designation means 62 % by weight of Sn, 35.7% Pb, 2%, Ag, 0.3% Sb, RMA flux, 75 µm average particle size, 85% metal content, viscosity 400 000 - 600 000 centipoise.

Electronic Pack….. Chapter 7 Production of PCBs.


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Solder Paste, continued

Fig. 7.18: Test of solder paste: The paste is printed through a circular opening with a diameter of 5 mm, in a 200 µm thick stencil. After reflow, the paste should melt into one body, without any particles spreading out.

Electronic Pack….. Chapter 7 Production of PCBs.


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Screen Printing

  • Woven screen (stainless steel or polyester) with organic photosensitive layer, which is patterned with holes (mask).

  • Metal stencil with etched or drilled openings.

  • Polyester stencil with punched or drilled openings.

  • Definition and accuracy depends on type, mesh count, thickness, tension, squeegee, speed, etc. Screen Printing is a complex craft!

Electronic Pack….. Chapter 7 Production of PCBs.


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Screen Printing, continued

  • Off-contact for screen printing, contact for stencil. Two-step stencil for best definition.

  • The most advanced printers are fully automatic with vision system for alignment.

Electronic Pack….. Chapter 7 Production of PCBs.


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Surface Mounting, continued

Fig. 7.19: Detail of printing stencil (left) and printing screen with fine line printing pattern.

Electronic Pack….. Chapter 7 Production of PCBs.


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Surface Mounting, continued

Fig. 7.20: Detail of printing stencil with fine pitch printing pattern: Cross section of a stencil etched from both sides, with an acceptable, small amount of offset (40 x magnification).

Electronic Pack….. Chapter 7 Production of PCBs.


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Surface Mounting, continued

Fig. 7.21: Two steps printing stencil.

Electronic Pack….. Chapter 7 Production of PCBs.


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Surface Mounting, continued

Fig. 7.22: Printing through 0.3 mm diameter holes with Mylar stencil. To obtain the correct amount of solder paste two or three small holes may be used for each solder land.

Electronic Pack….. Chapter 7 Production of PCBs.


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Surface Mounting, continued

Fig 7.23 a): Screen printer.

Electronic Pack….. Chapter 7 Production of PCBs.


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Surface Mounting, continued

Fig. 7.23 b): The squeegee (DEK).

Electronic Pack….. Chapter 7 Production of PCBs.


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IR Soldering

Fig. 7.24 a): IR furnace. Schematically with low temperature "area emitter".

Electronic Pack….. Chapter 7 Production of PCBs.


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IR Soldering, continued

Fig. 7.24 b): Industrial IR furnace.

Electronic Pack….. Chapter 7 Production of PCBs.


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Infrared Soldering

  • Planck´s law:

    W/A = k1/l5 {exp(k2/lT)-1}

    Shown on graph, where:

    W/A = emitted energy pr. second per m2

    area per micrometer of radiation spectrum

    k1 = 2 hc2 h = Planck´s constant

    k2 = hc/k k = Boltzmann’s constant

    Wavelength of max. radiation:

    lmax = k3/T

  • Total radiated energy (Stefan Boltzmann´s law): W/A = esT4

    s = Stefan Boltzmann’s constant

    e = emissivity (between 0 and 1)

Electronic Pack….. Chapter 7 Production of PCBs.


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IR Soldering, continued

Fig. 7.25: Typical temperature profile for an IR furnace.

Electronic Pack….. Chapter 7 Production of PCBs.


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Vapor Phase Soldering

  • Newton´s law :

    dQ/dt = h•A (Tf -Ts)

    Where:

    • dQ/dt = energy transferred pr. sec. (W)

    • A = total area

    • h = heat transfer coefficient

    • Tf = vapour temperature (boiling point)

    • Ts = PCB temperature

  • PCB temperature approaches Tf asymptotically:

    (Ts -To) = [Tf -To]•[1 -exp (-t/to)]

  • Electronic Pack….. Chapter 7 Production of PCBs.


    Vapour phase soldering l.jpg
    Vapour Phase Soldering

    Fig. 7.26 a): Principle of in-line vapour phase soldering machine.

    Electronic Pack….. Chapter 7 Production of PCBs.


    Vapour phase soldering continued l.jpg
    Vapour Phase Soldering, continued

    Fig. 7.26 b): Industrial in-line vapour phase soldering machine.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Vapour Phase Soldering, continued

    Fig. 7.27: Heat transfer coefficient for air and fluorocarbons. Boiling fluorocarbons, at the bottom, give 200 - 400 times more efficient heat transfer than air.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Vapour Phase Soldering, continued

    Fig. 7.28: Temperature profile through in-line vapour phase soldering machine.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Vapour Phase Soldering, continued

    Fig. 7.29: Chemical composition of fluoro carbons for vapour phase soldering. Top: The liquid FC-5311 (3M): C14 F24 is derived from C14 H10. Bottom: The liquid LS 230 (Galden).

    Electronic Pack….. Chapter 7 Production of PCBs.


    Vapour phase soldering continued42 l.jpg
    Vapour Phase Soldering, continued

    Table 7.1: Physical properties of some primary vapours for reflow soldering.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Other Soldering Methods

    • Hot air soldering (Most used today)

    • Impulse (hot bar-, thermode-) soldering

    • Hot plate / hot band soldering (thick film hybrid)

    • Laser soldering (too time-consuming single point soldering)

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Thermode Soldering

    Fig. 7.31: Two types of thermodes for thermode soldering.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Thermode Soldering, continued

    Fig. 7.32: Temperature profile for thermode soldering.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Component Placement

    • Automatic, dedicated pick-and-place machines

    • Manual placement (prototypes, repair)

    • Semi-manual (light guided table, etc.)

      • Programmable robot

      • Elements of Pick-and-Place Machine

        • Board magazine/feeder system

        • Mounting head(s) (with interchangable grip tools)

        • Programming/control unit

        • Component "storage" and feeder

        • Vision system (correct placement and control afterwards)

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Component Mounting

    Fig. 7.33: SMD pick-and-place machine (Siemens).The mounting head may also include an electronic vision system for very accurate placement of fine pitch components.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Component Mounting, continued

    Fig. 7.34: a): Mechanical gripper in a pick-and place machine.b): Detail of the component tape when a component is in position for picking. c): Vibration feeder.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Component Mounting, continued

    Fig. 7.35: Fuji CP-II pick-and-place machine. The machine has magazine for over 100 types of small components, nominal speed up to 15 000 components per hour, placement accuracy 0.10 mm. It has a rotating head with 12 positions, bottom figure, and two alternative tools at each position. There are components at all 12 positions at any time, with a separate operation being performed. A CCD camera shows the accurate position and orientation on a CRT screen (Fuji).

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Component Mounting, continued

    Fig. 7.36: Philips large hardware controlled pick-and-place machine.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Solder faults

    Fig. 7.38: Small SMDs standing on edge due to the "Manhattan-" or ”tombstone-" effect.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Robot System for Placement

    • Advantages:

      • Flexibility: Can handle most odd component types and boards, in low and high volumes

      • Uniform quality

      • High placement accuracy (~ 0.02 mm)

      • Non-manned operation (over night)

      • Can work in hostile environments

      • Tests and controls can be included in placement operation by special sensors on robot

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Robot Mounting

    Fig. 7.39: Example of a programmable placement robot for electronics: The SCARA robot.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Robot System for Placement

    • Must be carefully considered:

    • Cost, including the external equipment, fixtures, transport system

    • Lower capacity than Pick-and-Place

    • Requires careful planning, and often much dedicated surrounding equipment

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Robot Mounting, continued

    Fig. 7.40: The main components of a robot system.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Robot System Components

    • Manipulator

      • Learning unit

      • Control unit

    • Types of Manipulator Coordinate Systems

      • Cartesian

      • Cylindrical (including "Scara")

      • Spherical

      • "Human-like"

    Electronic Pack….. Chapter 7 Production of PCBs.


    Robot mounting continued57 l.jpg
    Robot Mounting, continued

    Fig. 7.41: Types of robot arms: a): Cartesian motion. b): Cylindrical. c): Spherical. d): "Human like". The SCARA robot is a special version of the cylindrical type.

    Electronic Pack….. Chapter 7 Production of PCBs.


    Robot system components continued l.jpg
    Robot System Components, continued

    • Programming

      • "Lead-and-learn”

      • "Jog-and-learn”

      • "Synthetic programming"

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Robot Mounting, continued

    Fig. 7.42: Multi gripper head.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Robot Uses in Electronics

    • Production

      • Component placement

      • Production of parts (coils, cables,....

      • Board feeding

      • Handling of boards, components in testing

      • Automatic trimming in test

      • Parts assembly for board, rack, chassis, etc.

      • Screw and glue operation

      • Soldering, welding

        • etc.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Robot Mounting, continued

    Fig. 7.43: Robot cell for electronic component placement (Adept)

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Types of Boards: SMD and Mixed Assembly

    • SMD side A

    • SMD side A and hole components side B

    • SMD side A and B

    • SMD both sides, hole components side B

    Electronic Pack….. Chapter 7 Production of PCBs.


    Process sequences l.jpg
    Process Sequences

    Fig. 7.44 a -d): Process sequences for boards with different types of components on the two sides.

    The steps marked "For all processes" on figure a) are not repeated on the other figures.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Process Sequences

    Fig. 7.44 a -d): Process sequences for boards with different types of components on the two sides.

    The steps marked "For all processes" on figure a) are not repeated on this figure.

    Electronic Pack….. Chapter 7 Production of PCBs.


    Process sequences65 l.jpg
    Process Sequences

    Fig. 7.44 a -d): Process sequences for boards with different types of components on the two sides.

    The steps marked "For all processes" on figure a) are not repeated on this figure.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Process Sequences

    Fig. 7.44 a -d): Process sequences for boards with different types of components on the two sides.

    The steps marked "For all processes" on figure a) are not repeated on this figure.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Board Testing

    • Functional test

    • "In-circuit" test

    • NB: Good designs use one-sided testing

      • Test jigs are expensive

      • Two-sided jigs very compicated

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Testing of PCBs

    Fig. 7.45: Two methods for single sided test of a board with components on both sides.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Testing of PCBs

    Fig. 7.46: Bed-of-nails test fixture.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Testing of PCBs

    Fig. 7.47:

    a) Detail of single sided test fixture.

    b) Double sided fixture.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Testing of PCBs

    Fig. 7.48: Two types of test pins.

    Electronic Pack….. Chapter 7 Production of PCBs.


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    Testing of PCBs

    Fig. 7.49: Unacceptable testing. The test point should be on the Cu foil on the board, not on the component lead.

    Electronic Pack….. Chapter 7 Production of PCBs.


    End of chapter 7 production of printed circuit boards l.jpg
    End of Chapter 7: Production of Printed Circuit Boards

    • Important issues:

      • When manufacturing PCBs:

        • Understand the basic manufacturing steps:

          • Sequencing and mounting of Hole Mounted Components

          • Wave soldering: Basics. Why we want to avoid (yield and reliability problems) When to use it for Surface Mount Components (Mixed boards)

          • Reflow soldering process: Basics. Solder paste. Silk screen and stencil printing. Reflow heating with hot air, IR, vapor phase, etc.

        • Component placement:

          • Automatic, manual, semi-automatic, and using robots

        • Types of SMD boards manufactured: Understand and remember the basic flow diagrams:

          • SMD side A

          • SMD side A and hole components side B

          • SMD side A and B

          • SMD both sides, hole components side B

        • Board testing:

          • Functional test

          • In-circuit test

    • Questions and discussions?

    Electronic Pack….. Chapter 7 Production of PCBs.


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