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Manufacturing Processes. Printed Circuit Board Assembly (PCB): Must specify or account for all components mounted into, onto or attached in some way to a printed circuit board as well as test for same

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Manufacturing processes
Manufacturing Processes

  • Printed Circuit Board Assembly (PCB): Must specify or account for all components mounted into, onto or attached in some way to a printed circuit board as well as test for same

    • Electrical Components: Passives, IC’s, Optical, ElecMech, ElecMag, Connectors, Switches, Sensors, Protection Devices, etc

    • Mechanical Components: Heat Sinks, Thermal Grease, Pullers, Stiffeners, Mounting Hardware, Sensors, Protection Devices, etc

  • High Level Assembly (HLA): Must specify or account for all elements or parts of an assembly level including testing

    • Electrical Elements: PCB’s, Cables, Harnesses, Fans, Power Supplies, Sensors, Protection Devices, User Displays, Switches, etc

    • Mechanical Elements: Enclosures, Feet, Standoffs, Card Guides, Gaskets, Sealants, Fasteners, Hardware, etc

Printed circuit board assemblies
Printed Circuit Board Assemblies

  • Printed Circuit Boards (PCBs):

    • Convenient form of interconnecting electrical components using industry standard attachment processes

    • 3 Basic Types of PCB-Component Assembly Technology

      • Thru Hole (TH)

      • Surface Mount (SMT)

      • Micro-electronic Multi-Chip-Module (MCM)

    • 3 Basic Types of PCB substrate systems (fabs)

      • Rigid epoxy including FR4, BT and others

      • Ceramic, Alumina (Al203), AlNi or other exotics

      • Flexible Substrate (flex circuit)

    • Single, Double and Multi-Layered

Manufacturing processes

  • PCB Manufacturing Guide Links










Manufacturing processes

Basic Photo-Etch

PCB Mfg Process

Plated Through Hole

PCB Cross Section

Via aspect ratio very important
VIA Aspect Ratio – Very Important

Bd Thickness

VIA Diameter

Aspect Ratio =

Aspect Ratios > 5 May Challenge Drilling, Plating & other PCB Mfg Processes

Cross Section Example of Failed VIA due to poor drilling, plating

Manufacturing processes

Cu PCB Trace Width & Depth

IPC Current Capacity Limitations

Manufacturing processes

Cu PCB Trace Conductor

IPC* Spacing vs Voltage Summary (*Simplified)

Manufacturing processes

Signal Routing is Important!

The PCB is part of the circuit

Good Signal Routing

Equal Lengths, Uniform

Good Power Bus Routing

Bypass Caps Closest to IC Power Pins

Poor Power Routing

Bypass Caps and 1 Conductor too Lengthy

Poor Signal Routing

Un-Equal Lengths, Non-uniform

Manufacturing processes

PCB Ionic Cleanliness is Important

  • Acetate & Formate - These organic acids can be extracted from some solder masks.  High levels can be indicative of an incompletely cured solder mask.  Incomplete cure can allow exposure of the copper traces to the environment resulting in corrosion and board failure.

  • Bromide:  Brominated compounds are added to laminates as a flame retardant.  Some laminates are employing alternate, non-bromine, flame retardants.  These are usually called specified as containing non-halogen flame retardants.  The surface bromide concentration is a function of the laminate heat history.  Bromide has also been identified as a component in some marking ink formulations and some solder masks.

  • Chloride - Chloride ions are the single most damaging material that can be on the board.  High levels are usually due to insufficient washing prior to applying the solder mask.  Chloride can also be transferred to the board by handling.

  • Nitrate and Ammonium - Both of these can be introduced in various plating processes.

  • Sulfate - Sulfate is rarely a problem.  High levels are usually caused by poor housekeeping:  dirty equipment, unpainted walls or unsealed floors.  

  • Sodium & Potassium - Sodium can be induced by handling but is also a component of tap water and may be indicative of poor water treatment.  In this case, chloride, calcium and magnesium should also be present. 

  • Calcium and Magnesium - Calcium and magnesium come from rinse water and are indicative of poor water quality. 

  • Citrate - Citrate salts and acids are components of some gold plating solutions.  They also are in many environmentally friendly cleaners.

IPC-6012 mandates the total ionic cleanliness prior to solder mask be <10ug/in2 in NaCl equivelants (IPC-TM-650)

Most Low Signal Or High Bias, High Reliability Designs Require Much Lower Levels on Individual Ions

Manufacturing processes

Thru-Hole Device Packages

  • Passives and Discretes

    • Axial Leaded (2 terminal, lying down)

      • Resistors, Capacitors, Inductors, Diodes

    • Radial Leaded (2 terminal, standing up)

      • Capacitors, Inductors, LEDs, MOVs, Power Resistors, …

    • T0 – Series (2-N terminals, Most Accommodate Std Heat Sink hardware)

      • T0-92 Small Signal Transistors, Regulators, References

      • T0-220 Moderate Power (~1W) Transistors, Regulators, Amplifiers

      • T0-3 Higher Power (~3W) Transistors, Regulators, Amplifiers

Manufacturing processes

Thru-Hole Device Packages

  • Integrated Circuits, Resistors, Relays

    • DIP (Dual In-Line Package)

    • PDIP, CDIP

    • SIP (Single In-Line Package)

    • Rectangular

Manufacturing processes

SMT – Surface Mount Technology Generations



Small Outline Package

Shrink SO Package

Thin Shrink SOP

Depopulated, Very Thin, Quad Flat Pack, No Leads

3 mm

Manufacturing processes







Fab, Comp


Bake, Clean

Simplified Comparison of Thru Hole and SMT PCB Assembly Process





Thru Hole


Solder Paste




Vision System Inspection




Wave Solder

Vision System Inspection






Stresses and Test Processes

Vision/Xray System Inspection

Manufacturing processes


Screen Print

SMT Placement


Hand Assembly

Wave Solder

Final Assembly


In Circuit Test

Stress Screen

Functional Test

Pack / Ship

Typical SMT Complex Circuit Board Assembly Processes

Ipc institute of printed circuits www ipc org association connecting electronics industries
IPC = Institute of Printed Circuits, WWW.IPC.ORGAssociation Connecting Electronics Industries

  • IPC-A-610 Acceptability of Electronic Assemblies

  • IPC-6011 Series of Board PCB Performance Standards

  • IPC/EIA J-STD-001 Requirements for Soldered Electrical and Electronic Assemblies

  • IPC-7095 Design and Assembly Process Implementation for BGAs

  • IPC-2221 Generic Std for Printed Board Design

  • IPC-D-279 Design Guidelines for Reliable Surface Mount Technology Printed Board Assemblies


Ipc electronic assembly classifications
IPC Electronic Assembly Classifications

  • High Reliability Electronic Products:

    • Continued performance, performance on demand, and extended life is critical and equipment downtime cannot be tolerated. Equipment must function when required with a high level of reliability assurance.

    • End-use environment is harsh

    • Includes equipment for commercial, military products, and for such applications as life support or missile systems.

  • Dedicated Service Electronic Products:

    • Continued performance, extended life and uninterrupted service is desired but not critical.

    • Typically the end-use environment would not cause failures

    • Includes communications equipment, sophisticated business machines, instruments and military equipment

  • General Electronic Products:

    • Function of the completed assembly is the major requirement

    • Cosmetic imperfections are not important

    • Includes consumer, some computer, peripherals, general military HW

Aerospace, Military

10 Yr Stresses

# of Bds, # of solder joints

# of Mechanical Cycles

4# of Power Cycles

# of Therm Cycles, Excursion


Ref: IPC-A-610, IPC-JSTD-001, IPC-7095

Telecom & Certain Medical

Ipc workmanship classes solder volume shape placement control

100 %

75 %

50 %

25 %

0 %

100 %

75 %

50 %

25 %

0 %

IPC Workmanship Classes: Solder Volume, Shape, Placement Control

  • High Reliability Electronic Products: Includes the equipment for commercial and military products where continued performance or performance on demand is critical. Equipment downtime cannot be tolerated, and functionality is required for such applications as life support or missile systems. Printed board assemblies in this class are suitable for applications where high levels of assurance are required and service is essential.

    • Requirement for Aero-Space, Certain Military, Certain Medical

  • Dedicated Service Electronic Products: Includes communications equipment, sophisticated business machines, instruments and military equipment where high performance and extended life is required, and for which uninterrupted service is desired but is not critical. Typically the end-use environment would NOT cause failures.

    • Requirement for High Eng Telecom, COTS Military, Medical

  • General Electronic Products: Includes consumer products, some computer and peripherals, as well as general military hardware suitable for applications where cosmetic imperfections are not important and the major requirement is function of the completed printed board assembly.

  • Min PTH Vertical Fill: Class 2 = 75% Class 3 = 100%

    Ref: IPC-A-610, IPC-JSTD-001

    Bga void size and locations uniform void position distributions
    BGA Void Size and Locations,Uniform Void Position Distributions








    Void_Solder Interface Distance

    S = Shell

    Potential for Early Life Failure (ELFO) if S < D/10 = (solder_joint_radius)/10

    S =Shell = solder_joint_radius – (void_distance + void_radius)

    Manufacturing processes

    CLASS 1

    Solder Joint_Radius: 0.225 mm

    Void_Radius: 0.135 mm

    Void_Area: 36% of Joint Area

    Failure criteria: D/10

    P(D<10) = 81.11 %

    CLASS 2

    Solder Joint_Radius: 0.225 mm

    Void_Radius: 0.1013 mm

    Void_Area: 20% of Joint Area

    Failure criteria: D/10

    P(D<10) = 52.21 %

    CLASS 3

    Solder Joint_Radius: 0.225 mm

    Void_Radius: 0.0675 mm

    Void_Area: 9% of Joint Area

    Failure criteria: D/10

    P(D<10) = 27.00 %

    Manufacturing processes
    Class vs Shell Size Relative Probabilities~ 2x more likely to exceed D/10 threshold with Class 2 vs Class 3

    S = Shell


    Manufacturing processes

    Physics of Failure: Accumulated Fatigue Damage (AFD) is related to the number of stress cycles N, and mechanical stress, S, using Miner’s rule

    Exponent Bcomes from the S-N diagram. It is typically ~3 for 63/37 SnPb Solders

    Example: Solder Joint




    Effective cross-sectional

    Area: D/2

    Effective cross-sectional

    Area: D


    Applied stress:

    Applied stress:

    Let  = 10, then

    AFD with voids will “age” about

    1000x faster than AFD with no voids

    Voids in solder joints

    Ipc a 610 conditions
    IPC-A-610 Conditions

    • IPC-A-610 Workmanship Conditions

      • Target Condition- This is the most desired condition and previously was referred to as preferred. It is not always essential to achieve this condition for reliability considerations.

      • Acceptable Condition- is a condition that, while not at a Target Condition, will result in a reliable product for the application. Corrective actions shall be directed to move toward the Target Condition.

      • Nonconforming Process Indicator- Is when a condition exists which does not affect the use of the product, but is not optimum. May result in repair, rework or scrap depending upon the customer’s requirements. Corrective action is necessary to bring the result back toward the Target.

      • Nonconforming Defect Condition- is when a condition exists that does not meet the reliability or performance in the application. Correction action is mandatory.

        All the IPC-A-610 Measurements utilize

        • Temp (Deg F/C)

        • Mass (Oz/Kg)

        • Distance (mils/mm)

    There are three key words used in the workmanship standards: Must, Shall and Should.

    Must means mandatory for Class 1, 2, & 3

    Shall means mandatory for Class 3 only.

    Should means recommended only for Class 1,2 & 3.


    Solder joints
    Solder Joints

    • Solder Joints: A solder joint is formed when two metal surfaces are soldered together. The solder fills the void between the surfaces and is the area most important. It provides the majority of “strength of attachment.” A solder fillet is formed after the solder joint is filled, and, is the visible solder verifying the presence of the solder joint.

      • Blow Hole Defects: Blowholes are solder voids visible from the surface going into the solder joint alongside a through-hole lead. A blowhole is a nonconforming process indicator provided the solder connection meets the minimum circumference and depth requirements.

      • Dewetting Defects: Solder joints are visually inspected for wetting characteristics. Dewetting occurs because the flux has been burned off and moisture attacks the surfaces. A good indicator of dewetting is solder pooling and pulling back off leads or lands.

      • Oxidation Defects: When moisture in the air attacks a solder joint, it forms a protective rust-like layer. This is referred to as oxidation, which attacks metal surfaces. Oxidation dramatically reduces the transfer efficiency of thermal energy.

      • Dimensional Defects: For any of the above in addition to poor placement, screening, reflow and other processes, solder joint geometric defect limits are clearly specified in these Stds (see above)

    Discrete component geometries
    Discrete Component Geometries

    NOTES1. The maximum fillet may overhang the land or extend onto the top of the chip cap metallization; however the solder shall not extend further onto the component body.2. Properly wetted fillet evident.

    J lead component geometries
    J-Lead Component Geometries

    NOTES1. The maximum solder fillet shall not touch package body. 2. Properly wetted fillet evident.

    Gull wing component geometries
    Gull Wing Component Geometries

    NOTES1. Solder fillet may extend through the top bend. Solder must not touch the package body or end seal, except for low profile SMD devices, e.g., SOICs, SOTs. Solder should not extend under the body of low profile surface mount components whose leads are made of Alloy 42 or similar metals.2. Must not violate minimum design conductor spacing.3. Properly wetted fillet evident.

    Thru hole component geometries
    Thru-Hole Component Geometries

    NOTES1. Wetted solder refers to solder applied by the solder process.2. The 25% unfilled volume includes both source and destination side depressions.

    Ic packaging progression

    Surface Mount

    CSP / WLP

    (CSP = Chip Scale Package, WLP = Wafer Level Package)

    IC Packaging Progression:

    Through Hole


    • 25 mil pitch

    • Limited by perimeter leads


    • Area array 0.8 mm to 0.5 mm

    • Limited by substrate wiring

    • 100 mil pitch

    • Limited by through hole spacing

    Fujitsu supercsp
    Fujitsu SuperCSP


    Trace (Cu)


    Al Pad

    • Solder balls on copper posts

    • Redistribution wiring to posts

    • Encapsulant is molded onto wafer

    Polyimide Layer



    Barrier Metal

    Solder Ball

    Metal Post (Cu)

    Manufacturing processes

    Wafer Level Packaging Will Become Std



    • Chip Scale

    • CSP

    • Wafer Level

    • Stacked Die

    • SiP

    • Surface Mount

    • QFP

    • TSOP

    • SOJ

    • BGA

    • Thru Hole

    • DIP

    • Pin Grid





    Manufacturing processes


    Flip-Chip Underfill+


    0.25 mm grid




    0.5 mm grid



    Pins (#)





    Analog ICs


    Power ICs







    Die Area (mm2)

    Process flow wafer level packaging vs conventional packaging
    Process Flow:Wafer Level Packaging vs. Conventional Packaging

    * From Motorola