Transcript Flexible Printed Wiring Board

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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Electronic Pack….. Chapter 7 Production of PCBs.
Slide 1
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
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Slide 2
Hole Mounting, continued
Fig. 7.2 a): Schematic example of the most efficient sequence of
mounting the components of a particular PCB.
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Slide 3
Hole Mounting, continued
Fig. 7.2 b): The principle of sequencing.
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Slide 4
Hole Mounting, continued
Fig. 7.3: Sequencing machine.
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Slide 5
Hole Mounting, continued
Fig. 7.4: Axial inserter with two mounting heads.
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Slide 6
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.
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Slide 7
Hole Mounting, continued
Fig. 7.6: DIP inserter.
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Slide 8
Hole Mounting, continued
Fig. 7.7:
Manual
mounting
board with
light guide.
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Slide 9
Hole Mounting, continued
Fig. 7.8:
Wave
soldering
machine.
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Slide 10
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
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Slide 11
Wave Soldering, continued
•Fluxing
•Pre-heating
•Soldering
•(Cleaning)
Fig. 7.9:
a): Principle of foam
fluxer.
b): Control system for
density and level of the
flux bath.
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Slide 12
Wave Soldering, continued
Fig. 7.10:
a): Principle
of wave
soldering.
b): The real
shape of the
wave.
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Slide 13
Wave Soldering, continued
Fig. 7.11:
a): Industrial in line
cleaning machine.
b): The principle of
ultrasound and
vapour cleaning.
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Slide 14
ElectroStatic Discharge
(ESD) Precautions
Fig. 7.12: An ESD protected working space. The resistors
R normally are 100 Kohm - 1 Mohm.
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Slide 15
Surface Mounting
• Soldering by
wave solder
process or by
reflow process
Fig. 7.13:
Application of
adhesive for SMD
mounting by:
a): Stencil or screen
printing
b): Dispensing
c): Pin transfer
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Slide 16
Surface Mounting, continued
Fig. 7.14:
a): Shadowing in SMD wave soldering.
b): Solder bridging on fine pitch package.
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Slide 17
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.
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Slide 18
Surface Mounting, continued
Fig. 7.16: Temperature profile during wave
soldering in a double wave machine.
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Slide 19
Reflow Solder Process
• Print solder paste
• Mount components
• Dry solder paste
• Solder by heating to melting of paste
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Slide 20
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
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Slide 21
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.
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Slide 22
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.
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Slide 23
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!
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Slide 24
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.
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Slide 25
Surface Mounting, continued
Fig. 7.19: Detail of printing stencil (left) and
printing screen with fine line printing pattern.
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Slide 26
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).
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Slide 27
Surface Mounting, continued
Fig. 7.21: Two steps printing stencil to give less
solder paste deposited.
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Slide 28
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.
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Slide 29
Surface Mounting, continued
Fig 7.23 a): Screen printer.
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Slide 30
Surface Mounting, continued
Fig. 7.23 b): The squeegee (DEK).
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Slide 31
Convection Soldering
Convection soldering oven.
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Slide 32
Convection Soldering
Convection soldering oven: Temperature profile on PC screen.
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Slide 33
IR Soldering
Fig. 7.24 a): IR furnace. Schematically with low
temperature "area emitter".
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Slide 34
IR Soldering, continued
Fig. 7.24 b): Industrial IR furnace.
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Slide 35
IR Soldering, continued
• Infrared Soldering
• Planck´s law:
W/A = k1/l5 {exp(k2/lT)-1}
– 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)
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Slide 36
IR Soldering, continued
• Graph of Planck`s
law:
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Slide 37
IR Soldering, continued
Fig. 7.25: Typical temperature profile for an IR furnace.
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Slide 38
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)]
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Slide 39
Vapour Phase Soldering
Fig. 7.26 a): Principle of in-line vapour phase soldering machine.
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Slide 40
Vapour Phase Soldering,
continued
Fig. 7.26 b): Industrial in-line vapour phase soldering machine.
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Slide 41
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.
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Slide 42
Vapour Phase Soldering,
continued
Fig. 7.28: Temperature profile through in-line vapour phase
soldering machine.
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Slide 43
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).
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Slide 44
Vapour Phase Soldering,
continued
Property
Boiling point or range
Molecular weight
Pour point
Density of liquid at 25°C
Density of saturated vapour at BP
Viscosity of liquid at 25°C
Surface tension of liquid at 25°C
Specific heat of liquid at 25°C
Thermal conductivity at 25°C
Electrical resistivity
Heat of vaporisation, at BP
Units
°C
°C
g cm3
mg cm3
cP
mN/m
J/gK
mW/mK
Ohm cm
J/g
R113 FC-70 FC-5311
47,6 215
215
187 821
624
-25
-20
1,57 1,93
2,03
7,38 20,3
15,6
LS230
230±5
~650
-80
1,82
19,5
0,7
19
0,95
74
27
18
1,05
70
2 1015
16
19
1,07
53
>1015
8
18
1,00
70
1015
67
68
63
Table 7.1: Physical properties of some primary vapours for reflow
soldering.
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Slide 45
Other Soldering Methods
• Impulse (hot bar-, thermode-) soldering
• Hot plate / hot band soldering (thick film
hybrid)
• Hot air soldering
• Laser soldering
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Slide 46
Thermode Soldering
Fig. 7.31: Two types of thermodes for thermode soldering.
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Slide 47
Thermode Soldering,
continued
Fig. 7.32: Temperature profile for thermode soldering.
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Slide 48
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
–
–
–
–
–
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Board magazine/feeder system
Mounting head(s) (with interchangable grip tools)
Programming/control unit
Component "storage" and feeder
(Vision system)
Electronic Pack….. Chapter 7 Production of PCBs.
Slide 49
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.
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Slide 50
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.
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Slide 51
Component Mounting,
continued
Fig. 7.35: Fuji CP-II pick-andplace 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).
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Slide 52
Component Mounting,
continued
Fig. 7.36: Philips large hardware controlled pick-and-place machine.
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Slide 53
Solder faults
Fig. 7.38: Small SMDs standing on edge due to the
"Manhattan-" or ”tombstone-" effect.
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Slide 54
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
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Slide 55
Robot Mounting
Fig. 7.39: Example of a programmable placement robot for
electronics: The SCARA robot.
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Slide 56
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
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Slide 57
Robot Mounting, continued
Fig. 7.40: The main components of a robot system.
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Slide 58
Robot System Components
• Manipulator
–Learning unit
–Control unit
• Types of Manipulator Coordinate Systems
–Cartesian
–Cylindrical (including "Scara")
–Spherical
–"Human-like"
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Slide 59
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.
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Slide 60
Robot System Components,
continued
• Programming
–"Lead-and-learn”
–"Jog-and-learn”
–"Synthetic programming"
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Slide 61
Robot Mounting, continued
Fig. 7.42: Multi gripper head.
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Slide 62
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.
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Slide 63
Robot Mounting, continued
Fig. 7.43: Robot cell for electronic component
placement (Adept)
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Slide 64
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
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Slide 65
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.
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Slide 66
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.
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Slide 67
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.
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Slide 68
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.
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Slide 69
Board Testing
• Functional test
• "In-circuit" test
• NB: Good designs use one-sided testing
–Test jigs are expensive
–Two-sided jigs very compicated
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Slide 70
Testing of PCBs
Fig. 7.45: Two methods for single sided test of a
board with components on both sides.
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Slide 71
Testing of PCBs
Fig. 7.46: Bed-of-nails test fixture.
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Slide 72
Testing of PCBs
Fig. 7.47:
a) Detail of
single sided
test fixture.
b) Double
sided fixture.
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Slide 73
Testing of PCBs
Fig. 7.48: Two types of test pins.
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Slide 74
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.
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Slide 75
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?
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Electronic Pack….. Chapter 7 Production of PCBs.
Slide 76