Printed Circuit Board
manufacturing
PCB (Printed Circuit Board
Board),
), NYÁK
PWB (Printed
(Printed Wiring Board
Board),
), NYHL
Wire network + mechanical support + base
of assembly
Benefits::
Benefits
• Higher load
load,, better dissipation
dissipation,, better
surface/
surface
/cross section ratio
• Automatic assembly, control,
control, and rework
• Better reliability
2
1
PCB types
• Laminates (substrates
substrates):
): rigid - flex
• Number of layers
layers::
• Single layer
• Double layers, through-hole plated,
• Multilayer
• Feature size
size:: width of conductiv and insulating stripes
• normal:
0,4 – 0,6 mm
• Fine :
0,3 – 0,4 mm
• Very fine: 0,1 – 0,2 mm
(1 raster = 2,54mm,
>16mil
~12 – 16 mil
~ 4 – 8 mil
1 mil = 0,01raster)
3
Main steps of manufacturing
•
•
•
•
•
Materials selection (laminate
laminate,, copper foil)
foil)
Mechanical forming (drilling, cutting
cutting))
Making hole conductiv
Galvanic plating
Patterning
– Photolithographie
Photolithographie,, screen printing
– Etching
• Soldermask
• Surface finishing
finishing:: metal plating (galvanic
galvanic,, immersion and
electroless))
electroless
4
2
Laminate materials
Insulating substrate
Requirements:
Requirements:
• Electrical
Electrical::
– Bulk resistance (specific ~: ρ)
– Surface resistance
– Dielectric konstans (ε
(ε, DK),
loss factor (D
(D,, tg
tgδδ)
– High frequency behavior
Dissipated power:
power:
Pv = U 2 ω C0 ε tgδ
• Thermal resistance
– Under joining
joining,, and joule heat
– Thermal expansion coefficient
coefficient,,
CTE (x,y,z
(x,y,z axis)
axis)
• Water absorption
• Mechanical
Mechanical::
– Strength
– Machinable (drilling,
cutting))
cutting
– Shouldn’t get buckled
The big CTE in z
axis cause
damage of the
plated copper
layer:
Depends on:
number of
layers,
thickness of the
copper layer and
thickness of the
5
laminate
6
3
Laminate materials
• Polymer resin
– Without reinforcements:
reinforcements:
Flex PCB,
– With reinforcements:
reinforcements:
rigid PCB
• Ceramics
(special applications only)
only)
•
7
Reinforcements::
Reinforcements
• Responsible for
strength,, stretch
strength
• Increase the heat
resistance and electrical
parameters..
parameters
– Paper
Paper,,
– Fiberglass
Fiberglass,,
– Wowen glass
– Ceramic fiber
Matrix,, resin
Matrix
• Responsible for the surface
surface,,
electrical and thermal
properties..
properties
– Phenolic resin (bakelit):
thermal resistance↓
resistance↓,
water↑
water
↑ absorption
– Epoxi resins:
resins: adhesion↑
adhesion↑,
electrical resistance ↑
– R&D: poliimid,
poliimid, teflon
(PTFE), liquid crystal
polymers (LCP)
8
4
Laminate types
FR series (flame
(flame retardant)
retardant)
• FRFR-2: paper reinforced phenolic
– Dark yellow,
yellow, stable size
• FRFR-3: paper reinforced epoxy
– Light beige,
beige, good electrical properties,
properties, suitable for hole
plating
• FRFR-4: wowen glass reinforced epoxi
– Transparent yellwish
yellwish--green,
green, good machinable,
machinable, plateale,
plateale,
minimal water absorption
• FRFR-5: similar to FRFR-4, better heat resistance,
resistance, higher Tg
• CEM 1: paper and glass reinforced epoxy
epoxy:: cheaper
9
The transformation temperature at different laminate
materials The CTE also changes at Tg 10
5
Properties
FRFR-3
FRFR-4
FRFR-5
Rbulk, Ωcm (40oC)
4 1012
8.1014
8.1014
R , Ω (40oC)
4 1012
3 1012
3 1015
εrel, (1 MHz)
4,9
4,7
4,6
tg
tgδδ (1 MHz) (GHz)
0,04
0,02
0,015
Tolerance of the solder
baath (sec)
25
>120
>120
Water absorption (mg)
na
15
na
Tg, glass transition
temperature
150
>165
Thermal expansion
coefficient (z axis %)
2525-275°
275°C
5.5
11
12
6
13
Rogers laminates
Copper foil
• Thickness
Thickness:: 17,5µ
17,5µm, 35µ
35µm, (70µ
(70µm, 105µ
105µm)
– Semi
Semi-additiv
additiv:: 5
5µ
µm Cu + protectiv coating
– special (eg
eg.. Car electronic 400 µm)
• Manufacturing
Manufacturing:: galvanoplastic
– Electroplating to a rotate
steel cilinder, detach after
half round
• Mounting
Mounting::
– Adhesiv foil or a dissolved
thermosetting resin
14
7
Maximal load of
copper stripes:
• marked temperature
mains the rising
•-the outer layers
tolerate double load
than inners
15
16
8
Preparations of the laminates
•Cutting
•Drilling
•Degreasing
•Micro
Micro-etching and dissolve the oxid
layer
Mechanical processes
Cutting:: usual size is 500 – 800m
• Cutting
Free border
Back end: routing
• Drilling: single side
side:: end of line, not
critical
Double side,
side, multilayer:
multilayer: key process,
process,
one of the first steps
steps.. Need a smooth
inner surface for metallization
Aspect ratio: hole lenght/
lenght/hole diameter
18
9
Drill tools
•
•
•
•
Material: TungstenMaterial:
Tungsten-carbide
(Slope
Slope):
): 30 – 40o
(Top angle):
angle): ~140o
Speed (rev):
rev):
1010-90000/min
smaller diameter,
diameter, higher
speed
• Min. d =0,2 – 0,15 mm
19
Suface cleaning
• Mechanical:
Mechanical: abrasiv cilinder, pumice
pumice,, ((wet
wet))
• Degreasing
Degreasing:: goal is the uniform adhesion of the new
coatings (photoresists
photoresists,, masks,
masks, metals)
metals)
– Water base materials:
materials:
• Lúgos: NaOH, Na2CO3, Na3PO4
• Detegents, surfactans
Dip or spray methods
20
10
• Organic solvents
– Good degreasing efficiency but toxic
toxic,, flameable
– Chlorinated paraffins (carbon tetrachlorid
tetrachlorid,,
trichlorotrichloro
-ethylene
ethylene)) – toxic
– Freons – cause ozon depletion
• Vapor phase cleaning:
cleaning: in a closed room,
room,
saturated vapor of iso
iso-propil
propil-alcohole
alcohole.. The
clear solvent condensed on the cold surface.
surface.
21
Ultrahangos tisztítás
• A hang longitudinális hullám nyomásváltozás
• Kavitációs üreg keletkezik - összeomlik,
• p = 108–109Pa, (folyadék – szilárd
határfelületen)
• Fellazítja, „letépi” a szennyeződést a
felületről
• Hatása függ: az oldószer
– Hőmérsékletétől,
– Gőznyomásától,
– Felületi feszültségétől
– Viszkozitásától
22
11
Ultrahangos tisztítás
•
•
•
•
f = 20 – 40kHz
Idő: 2 – 3 perc, (max. 10perc)
Forgatni kell
Oldószer: tiszta víz (meleg),
– lúgos zsírtalanító oldat,
– szerves oldószer, pl. aceton
23
Removing oxide layer
• Oxidized surface contains
contains:: Cu2O,
Cu
Cu(OH)
(OH)2·CuCO3,
• Decrease adhesion of the new films eg
eg..
photoresist,, metal
photoresist
• Usualy acid solvents
solvents:: sulfuric or
hydrochloride acids (10 – 20 % w/
w/W
W)
• Curing time
time:: 0,5 - 1 min at room
temperature
24
12
Printed Circuit Imaging
Photomask
Photolithographie
Sreen printing
Photomask preparation
Its role
role:: transfer the pattern
Master artwork:
artwork: the first,
first, original
drawing,, the copies are the
drawing
teghnological photos
• Manual methods: tint drawing,
peelable patterns (chartpack,
alfaset) →
contact photo
• Computer aided methods:
Circuit design programs
PCB design programs:
include: artworks (all layers), holes,
soldermasks, final controll driver
software
26
13
•x;y coordinates
Gerber fájl:
•Light on/off
•aperture size
Laser photoplotter
•Matrix printer
system
•Plotter system
•Very high resolution
27
Basics of phototechnics
Black and white film
Photosensitive layer
layer::
SilverSilver
-halogenide
particles disperged
in gelatine emulsion
Emulzió + fényérzékeny anyag
Hordozó
Emulsion
+ photosensitive crystals
Fényvédő réteg
Subsrate (transparent)
Protectiv layer
Structure of a film
28
14
Exposition - developing
• Exposition:
Exposition:
AgBr + hν → Ag + Br
latent picture
• Developing
Developing:: complete the reduction in the light
affected particles
29
AgBr crystals
crystals,, SEM
image
Exposed and partially
developed AgBr particles
30
15
Fixing:
Dissolve the unexposed AgBr
Hypo bath: Na2S2O3 ⇒ water soluble Ag
compound
31
Properties of photos
• Negative
• Sensitivity
Sensitivity::
– ISO/DIN
100/21, 200/24,
400/27
• Density
Density:: ((blackness
blackness,, opacity)
opacity) D = I0/I
– Contrast
Contrast,, tranprency
• Resolution
Resolution::
– Above 10000 dpi
– Resolution is in inverse ratio to the sensitivity
(bigger AgBr particle – higher sensitivity - lower
resolution))
resolution
32
16
Masking methodes
Goal: protect certain areas of the surface
Goal:
agains some physical or chemical attact
– In contact masks
– Out of contact
contact,, eg
eg:: screen mask
33
Photolithographie
• Photoresist
Photoresist,, photoimaigeable materials
• polimer layer
• Usable in PCB, hybrid IC and semiconductor
industry
• Resolution
Resolution,, ~ minimal line width → 20 nm
• types
types::
– positive
negative
– liquid
solid (film)
34
17
Photochemical background
• The absorbed photon give the energy quantum
to the reaction (bonding or activation energy
energy).
).
• W = hc
hc/
/λ ⇒ to the succesful reaction need a
given energy (λ is lower than a given value
value).
).
35
Types of photoresists
Positive:: Depolimerisation
Positive
caused by exposition,
exposition, the
molecular weight decreased,
decreased,
the solubility increased
increased..
Negative:: polimerisation
Negative
polimerisation,,
cross-linked bonds
crossformation influence
influence of light
light..
The photoresist get nearly
insoluble..
insoluble
Liquid
Solid
36
18
Polymer structures
Linear
Elágazó (branch?)
Cros-linked
37
Positive
Positiv
e resists
• Sensitive for UV, but
hardly for visible light
• Exposition
Exposition:: UV
• Developer
Developer:: diluted
NaOH (5 – 7 g/l)
• Stripper
Stripper:: organic
solvent
Negative
Negativ
e resists
• Sensitive for light under
540 nm (yellow light needs
in the workplace!)
Exposition:: UV
Exposition
• Developer: weak alkaline
solvent (1 – 2% Na2CO3)
• Stripper: stronger alkaline
solvent (5% NaOH)
38
19
Solid resists
• „+” , „„-”
the negative is more frequenty
used
• Thicker → important at the galvanisation
• Fewer mnufacturing steps
• Uniform layer thickness
Mylar (poliészter)
Reziszt film
PE
39
Manufacturing steps
(liquid resists
resists))
1. Clear
Clear,, degreased surface
2. Coating methods:
methods:
– Spin coating (d ~ vk ~ r )
– Screen printing
– Liquid carpet
3. Drying - 60…80oC
– The solvent is volatilized
– Film formation
40
20
41
Manufacturing steps 2
4. Exposition
–
–
–
Emulsion side stacked to the resist
UV - high
high-pressure Hg
Hg-vapor lamp (365nm)
-distance
distance,, time can count,
count, then experimental adjusting
(dose)
dose)
5. Developing
–
–
There is a difference only in solubility
solubility,, not soluble and
insoluble areas
The developer is spayed usually
6. Burning (positive only
only))
7. Etching
42
21
Manufacturing steps 3 - solid
resists
• Du Pont – Riston film
• Laminating 100oC, (panel is
preheated),
preheated
), surface is roughed
• Exposition
Exposition:: booth side
together,, precise positioning
together
• Develop
Develop::
– Remove mylar film,
– Develper is a weak alkaline
solution (1 – 2%2%-os Na2CO3),
– Spraying, need a mechanical
impact
43
Exposition methodes
•
•
•
•
Contact Imaging
Laser Projection Imaging
Imaging,, LPI
Laser Direct Imaging
Imaging,, LDI
Step and Repeat Imaging
44
22
Contact Imaging
•
•
•
•
•
•
•
•
Current, trouble
trouble--free processes,
Cheap instruments,
Good productivity,
productivity,
Low yield,
yield,
Manual positioning is inaccurate
inaccurate,,
Low resoution (~100 µm),
m),
Mas
Mask
k wearing,
wearing,
Granular waste
waste,, dust causes troubles
45
Laser projection system
46
23
•
•
•
•
Good resolution on bigger area,
Precise positioning,
Good productivity with traditional resists
resists,,
No contact betwen mask and panel, high
yield,,
yield
• It can make hole into the polymer layer
47
Developed resist patterns,
after laser imaging.
48
24
Laser direct imaging
49
•
•
•
•
Don’t need photomask
photomask,,
Very precise positioning
positioning,,
Suitable for prototyping or small series,
Fexible software, adapt to deformations,
deformations, psition
of the panel,
• Good yield
• Need a new,
new, very sensitive resist
resist,,
• The working time depends on the complexicity of
the circuit.
circuit.
50
25
Step and
repeat
Diminutive projection,
mainly for
semiconductor
industry
51
IC fotoresist technology
• Resolution: ~ 20 nm
• Exposition: deep UV,
93nm, monochromatic,
excimer laser
• Step ad repeat
• New optical materials
(transparent in this
wavelength eg
eg.. CaF2,
• New photoresist
materials:: sensitive in
materials
this wavelength
52
26
Masking methodes
Screen printing
Applications:
Medim or large volume
production
Medium feature size
•Eatch-resist mask
•Solder paste
•Legend
•Uniform layers of photoimigeable
liquids (solder mask)
54
27
Properties
Fiber properties:
Screen properties:
•Tensile strenght
•Flexibility
• Mesh number:
holes/inch ~ dpi
•Wear resistance
• Free area %
•Chemical
resistance
Materials:
• Polyester
• Metal (stainless 55
steel)
Parts of the screen
• Frame
• Emulsion
mask
• Filler
56
28
Types and preparation
• Direct (emulsion
emulsion))
• Liquid
Liquid,, fhotosensitive
emulsion::
emulsion
– dip coating
coating,,
– drying ,
– exposition
• Good adhesion , ~ 20000
copies
• Special illuminating box
57
Indirect photostecil
photostecil))
• Negativ photoimigeable
film (PVA, PVOH poly
poly--vinyl
acetate,, ~ alcohole)
acetate
• Exposition from the
direction of substrate
side!!
side
• Developer
Developer:: warm water
(40°
(40°C)
• Roll the soft mask into
the sreen
58
29
Micrscopic pictures
indirect
direct
59
Metal stencil
• Steel film, apertures cut
by:
– Laser
– (Electrocemical
Electrocemical)) etching
– Plasma etching
• Benefits:
– More precise,
– Better resolution (127 – 65
µm fine pitc IC
IC--s)
– Longer lifespan
(50 – 100 000 prints
prints))
– Good hardness and wear
resistant
Suitable for solder paste
printing
60
30
Electrochemically
etched apertures
Photolithographie – then
etching or galvanizing
(the stencil is anode)
Laser cut apertures
No photo, and chemicals,
Better reliability
61
Printing
• Table
Table:: fixing,
rögzítés,
positioning,,
positioning
quick change of
panels
• Squeegee
Squeegee::
– sharp
sharp,,
chemically
proof,, wearproof
wearproof
– Squeegi angle
angle::
45 – 60o,
printing speed
62
31
Paste properties
Viscosity: what is the
Viscosity:
optimum?
• Low
Low:: easy printing, the
printed dots will fuse
(overlap)
• High
High:: the printed pattern will
not flow away
⇒ tixotrop
Low
Low,, when the liquid flow,
high,, when it stay at rest
high
Surface tension
Paste types
•
•
•
•
Etch resist,
resist,
soldermask
soldermask,,
Solder paste
paste,,
Thick film HIC
functional materials
(conductiv
conductiv,, resistor
resistor,,
dielectric pastes
pastes),
),
• Inks for legende
63
Etchig
• Goal:
Goal: removig copper from the uncovered
areas..
areas
• Etchant
Etchant::
– Oxidativ
Oxidativ::
Cu → Cu2+ + 2e– acid
acid/
/alkaline pH:
keep Cu2+ solved
64
32
Etchant types:
types:
• Acid
Acid::
sulfuric
Sulfuric acid – hydrogen
hydrogen-peroxide H2SO4
ammónium--perszulfát (NH4)2S2O8
ammónium
chlorides
ferric chloride FeCl3
Copper(II)
Copper
(II)--chloride CuCl2
Copper--tetrammin complex
Copper
• Alkalic
Alkalic::
[Cu
Cu(NH
(NH4)4]2+
65
Etchant properties
• Rate of etching (µm/min)
– Depends on the temperature and the solvent
concentration
• Capacity (m2PCB/kg etchant)
etchant)
• Undercut
Undercut,, etch factor:
factor: ((vv ⊥/v )
• Selectivity (Sn mask on double layer PCB)
• Methode of regeneration
• Environmental and health impact
66
33
Etching methodes
• Dipping
• Spray
• Jet stream
– Always fresh etchant on the surface
– Dissolved copper washed by heavy flow
– Possibility of continuous regeneration (Copper
recovery, redox potential and pH correction)
• Rinse
– Minimal dropping out (air knife, rubber cylinder)
– The first rinse water is dangerous waste
– Cascade rinsing
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