Design for Mass Production Manufacturing Processes Printed Circuit
Design for Mass Production 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, ICs, 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: PCBs, Cables, Harnesses, Fans, Power Supplies, Sensors, Protection Devices, User Displays, Switches, etc Mechanical Elements: Enclosures, Feet, Standoffs, Card Guides, Gaskets, Sealants, Fasteners, Hardware, etc
Design for Mass Production 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 Design for Mass Production PCB Manufacturing Guide Links fullnet.com/u/tomg/gooteepc.htm ee.washington.edu/circuit_archive/text/design.html precisioncircuits.com.au/cid/hm_cid.html amscourseware.com/guidelines.htm filtranmicro.com/design.html goldengategraphics.com/pcgloss.htm elchempub.com/files/electroc2.htm pcbprotech.com/Dh3/DH3right.htm pcbprototyping.com/html/html_edu.htm Design for Mass Production Plated VIAs
Design for Mass Production Basic Photo-Etch PCB Mfg Process Plated Through Hole PCB Cross Section Design for Mass Production VIA Aspect Ratio Very Important Aspect Ratio = Bd Thicknes s VIA
Diameter Aspect Ratios > 5 May Challenge Drilling, Plating & other PCB Mfg Processes Cross Section Example of Failed VIA due to poor drilling, plating Design for Mass Production Cu PCB Trace Width & Depth IPC Current Capacity Limitations Design for Mass Production Cu PCB Trace Conductor IPC* Spacing vs Voltage Summary (*Simplified)
Design for Mass Production 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 Design for Mass Production 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 Design for Mass Production TH: Thru-Hole Technology Design for Mass Production Thru-Hole Device Packages Passives and Discretes Axial Leaded (2 terminal, lying down)
o Resistors, Capacitors, Inductors, Diodes Radial Leaded (2 terminal, standing up) o Capacitors, Inductors, LEDs, MOVs, Power Resistors, T0 Series (2-N terminals, Most Accommodate Std Heat Sink hardware) o T0-92 Small Signal Transistors, Regulators, References o T0-220 Moderate Power (~1W) Transistors, Regulators, Amplifiers o T0-3 Higher Power (~3W) Transistors, Regulators, Amplifiers Design for Mass Production Transistor Package Examples Design for Mass Production Thru-Hole Device Packages Integrated Circuits, Resistors, Relays
DIP (Dual In-Line Package) PDIP, CDIP SIP (Single In-Line Package) Rectangular Design for Mass Production
P-DIP (plastic) and C-DIP (ceramic) Examples Design for Mass Production SMT: Surface Mount Technology Design for Mass Production SMT Surface Mount Technology Generations 20mm DIP Small Outline Package Shrink SO Package Thin Shrink SOP 3 mm
Depopulated, Very Thin, Quad Flat Pack, No Leads Design for Mass Production Discretes: Rectangular 0402) (Example Design for Mass Production SOT Small Outline Transistors (SOT-3, SOT-223) Design for Mass Production QFP Quad Flat Packs Design for Mass Production
Quad Flat Pack QFP, PQFP Design for Mass Production PLCC Plastic Leaded Chip Carriers Design for Mass Production BGA Ball Grid Arrays Design for Mass Production Typical BGA Pin Layout Design for Mass Production Electronic Assembly Quality Design for Mass Production
Electronic Assembly Quality and Standards Design for Mass Production Component Procure Setup Substrate (Fab) Fabrication Fab, Comp Prep Bake, Clean Thru Hole
Mechanical Hand Operations Simplified Comparison of Thru Hole and SMT PCB Assembly Process SMT Screen Solder Paste Auto Component Insertion
Vision System Inspection Auto Component Placement Wave Solder Vision System Inspection Reflow Solder (Oven) Lead Trim
Stresses and Test Processes Vision/Xray System Inspection Design for Mass Production Setup Screen Print SMT Placement Hand Assembly
Wave Solder Final Assembly In Circuit Test Stress Screen Functional Test Reflow Wash Pack / Ship Typical SMT Complex Circuit Board Assembly
Design for Mass Production Solder Geometry Variability in SMT and THT Design for Mass Production IPC = Institute of Printed Circuits, WWW.IPC.ORG Association 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 Quality! Design for Mass Production IPC Electronic Assembly Classifications 3. High Reliability Electronic Products: Ref: IPC-A-610, IPC-JSTD-001, IPC-7095
PROCESS CONTROL PROCESS QUALITY 4. 5. Aerospace, Military 10 Yr Stresses Continued performance, performance on demand, and extended life is critical and equipment downtime cannot be tolerated. Equipment must # of Bds, # of solder joints function when required with a high level of reliability assurance.
# of Mechanical Cycles End-use environment is harsh 4# of Power Cycles Includes equipment for commercial, military products, and for such applications as life support or missile systems. # of Therm Cycles, Excursion Dedicated Service Electronic Products: Telecom & Certain Medical 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 Design for Mass Production IPC Workmanship Classes: Solder Volume, Shape, Placement Control 3. 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. 4.
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. 5. Requirement for Aero-Space, Certain Military, Certain Medical 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. 100 %
100 % 75 % 75 % 50 % 50 % 25 % 25 % 0%
0% Min PTH Vertical Fill: Class 2 = 75% Ref: IPC-A-610, IPC-JSTD-001 IPC-7095 BGA Std Class 1 Class 2 Class 3 Max Void Size 60% Dia
36% Area 45% Dia 20.3% Area 30% Dia 9% Area Max Void Size at Interfaces 50% Dia 25% Area 35% Dia 12.3% Area
20% Dia 4% Area Class 3 = 100% Design for Mass Production BGA Void Size and Locations, Uniform Void Position Distributions Sampling_Grid Position Model Solder_Joint_Radius Void_Distance Void_Radius
S 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) Design for Mass Production 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 % Design for Mass Production Class vs Shell Size Relative Probabilities ~ 2x more likely to exceed D/10 threshold with Class 2 vs Class 3 S = Shell Depth Design for Mass Production Physics of Failure: Accumulated Fatigue Damage (AFD) is related to the number of stress cycles N, and mechanical stress, S, using Miners rule Exponent B comes from the S-N diagram. It is typically ~3 for 63/37 SnPb Solders Example: Solder Joint Shear
voids Effective cross-sectional Effective crossForce Area: D/2 F sectional Area: D Applied stress: Let = 10, then Applied stress: AFD with voids will age about
1000x faster than AFD with no voids Voids in solder joints Design for Mass Production 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 customers 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 There are three key words used in the workmanship standards: Must, Shall and Should. Temp (Deg F/C) Mass (Oz/Kg) Distance (mils/mm)
Must means mandatory for Class 1, 2, & 3 Shall means mandatory for Class 3 only. Quality! Should means recommended only for Class 1,2 & 3. Design for Mass Production 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) Design for Mass Production Discrete Component Geometries NOTES 1. 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. Design for Mass Production J-Lead Component Geometries NOTES 1. The maximum solder fillet shall not touch package body. 2. Properly wetted fillet evident.
Design for Mass Production Gull Wing Component Geometries NOTES 1. 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. Design for Mass Production Thru-Hole Component Geometries NOTES 1. Wetted solder refers to solder applied by the solder process. 2. The 25% unfilled volume includes both source and destination side depressions.
Design for Mass Production Advanced Packaging Design for Mass Production Through Hole Surface Mount CSP / WLP (CSP = Chip Scale Package, WLP = Wafer Level Package) TSOP CSP/WLP
25 mil pitch Area array 0.8 mm to 0.5 mm Limited by perimeter leads Limited by substrate wiring 100 mil pitch Limited by through hole spacing IC Packaging Progression: Design for Mass Production Fujitsu SuperCSP Redistribution Trace (Cu)
SiN Al Pad Polyimide Layer Die Encapsulant Barrier Metal Solder Ball Metal Post (Cu) Solder balls on copper posts Redistribution wiring to posts Encapsulant is molded onto wafer
Design for Mass Production Wafer Level Packaging Will Become Std ns e D VOLUME i ty Thru Hole DIP Pin Grid 1960
Surface Mount QFP TSOP SOJ BGA 1980 2000 YEAR Chip Scale CSP Wafer Level Stacked Die SiP
Design for Mass Production 10000 Flip-Chip Underfill+ m 5 2 0. 1000 m m 0.5
Pins (#) id gr m gr Processor HDI id ASICs
B PW DRAM SRAM Flash 100 Passives Analog ICs 10 Power ICs Discretes 1 1
10 100 Die Area (mm2) 1000 Design for Mass Production Process Flow: Wafer Level Packaging vs. Conventional Packaging * From Motorola
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