Transcript Flexible Printed Wiring Board

Chapter 3
Materials and Basic Processes
Picture of the
chip set of
SensoNor’s
SP13 Tire
Pressure
Sensor
The course material was developed in INSIGTH II, a project
sponsored by the Leonardo da Vinci program of the European Union
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 1
Materials: Metals
• Right choice, right use and compatibility of
materials is the key to good packaging and
optimal properties.
–Elemental metals:
• High electrical conductivity
• High thermal conductivity
• Higher thermal coefficient of expansion (TCE) than
semiconductors and most ceramics
–Alloys: taylored to many uses:
• Poorer electrical and thermal conductivity than elements
• Taylored TCE
• Lower melting point
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 2
Metals, continued
Table 3.1 a): Properties of some important materials in electronics: Conductors[3.1].
Electrical
Thermal
Thermal
Melting Point
Resistivity
Exp. Coeff.
Conductivity
Metal/Conductor
[°C]
[10-8Ohmm]
[10-7/°C]
[W/m.°K]
Copper
1083
1.7
170
393
Silver
960
1.6
197
418
Gold
1063
2.2
142
297
Tungsten
3415
5.5
45
200
Molybdenum
2625
5.2
50
146
Platinum
1774
10.6
90
71
Palladium
1552
10.8
110
70
Nickel
1455
6.8
133
92
Chromium
1900
20
63
66
Invar
1500
46
15
11
Kovar
1450
50
53
17
Silver-Palladium
1145
20
140
150
Gold-Platinum
1350
30
100
130
Aluminium
660
4.3
230
240
Au-20%Sn
280
16
159
57
Pb-5%Sn
310
19
290
63
Cu-W(20%Cu)
1083
2.5
70
248
Cu-Mo(20%Cu)
1083
2.4
72
197
• (Table 3.1)
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 3
Metal Alloys
• Fig. 3.1:
Phase diagram
for Sn/Pb. The
eutectic mixture
63%/37% has a
melting point of
183°C.
• Alloys have poorer conductivity, both electrical and thermal.
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 4
Insulators
Table 3.1 b):
Properties of important materials in electronics: insulators [3.1].
Relative
Thermal Exp.
Thermal
Approximate
Dielectric
Coefficient
Conductivity
Processing
Constant
Non Organics
[10-7/ oC]
[W/ m.oK]
Temp.[oC]
92% Alumina
9.2
60
18
1500
96% Alumina
9.4
66
20
1600
Si3N4
7
23
30
1600
SiC
42
37
270
2000
AlN
8.8
33
230
1900
BeO
6.8
68
240
2000
BN
6.5
37
600
>2000
Diamond - High Pressure
5.7
23
2000
>2000
Diamond - Plasma CVD
3.5
23
400
1000
Glass-Ceramics
4-8
30-50
5
1000
Cu Clad Invar
(10%Cu)/ (Glass Coated)
30
100
800
Glass coated Steel
6
100
50
1000
Organics
Epoxy-Kevlar(x-y) (60%)
3.6
60
0.2
200
Polyimide-Quartz (x-axis)
4.0
118
0.35
200
Fr-4(x-y plane)
4.7
158
0.2
175
Polyimide
3.5
500
0.2
350
Benzocyclobutene
2.6
350-600
0.2
240
Teflon (™DuPont Co.)
2.2
200
0.1
400
• (Fig 3.1b)
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 5
Semiconductors, Si and GaAs
• High thermal
conductivity
• Electrical conductivity
spans many orders of
magnitude, depending
on doping
• Very low TCE
• "Machinable" by
anisotropic etching (Si)
• Excellent protective
oxide (Si)
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 6
Ceramics
• Inorganic, non-metallic
• Made by powder, compressing or tape casting,
and high temperature treatment (600-1800oC)
• Chemically and thermally very stable
• Electrical insulators
• Some ceramics are very good thermal
conductors
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 7
Ceramics, continued
Table 3.1 c):
Properties of ceramics, Si, Si3N4 and SiO2 and polyimide.[3.1]
Characteristic
Specific Resistance
(Ohmcm)
Al2O3
AlN
>1014 4x1011
Relative Permittivity
Thermal
Conductivity (W/m °K)
Thermal Expansion
Coefficient (10-6/°K)
Breakdown Field
Strength (V/cm)
Loss Factor (tan )
Modulus of Elasticity
(kN/mm2)
19.01.2011
9.8
10 to
35
10
140 to
170
5.5
2.65
SiO2
Si3N4 Polyimide
1013
Si
10-4 to
10+4
106
1012
1016
15 to
45
11.9
3.9
3-4
270
150
3.7
2.6
1.5
0.3 to
0.5
7.5
10 to
40
2.5 to
3
SiC
106 to 106 to
700
105
105
105
107
107
_
4x10-3
5x10-4
3x10-4 to 10-3 5x10-2 4x10-2 3x10-2
70 to 280 to
300 to
320
72.5
170
380
300
380
Electronic Pack….. Chapter 3 Materials and Basic Processes
0.4
20 to
70
106
_
3
Slide 8
Ceramics, continued
• Dielectric loss:
– tan  = (1/R)/wC = 1/Q
– e = eo (k´ - jk")
– tan  = k"/k´.
Cp
Rp
• Main uses:
–Substrates for hybrid circuits, component
packages, SMD resistors
–Multilayer capacitors
–Future: Superconductors ?
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 9
Materials
Table 3.1 d):
Elastic modules and thermal conductivity of some materials [3.1].
Modulus of
Thermal
Application
Elasticity E Conductivity k
Material
[GPa]
[W/cm °C]
90-99% Al2O3
262
0.17
Substrate
Beryllia (BeO)
345
2.18
Substrate
Common Cu alloys
119
2.64
Leadframe
Ni-Fe Alloys(42 alloys)
147
0.15
Leadframe
Au-20% Sn
59.2
0.57
Die bond attach and lid
sealant
Au-3% Si
83
0.27
Die bond attach
Pb-5% Sn
7.4
0.63
Flip chip bonding
Silicon
13.03
1.47
Electronic circuit
Au
78
3.45
Wire metallurgy
Ag-loaded epoxy
3.5
0.008
Die bond adhesive
Epoxy (Fused silica filler)
13.8
0.007
Moulding Compound
• Fig 3.1.d
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 10
Ceramics, continued
Table 3.1 e): Properties of low temperature ceramic. Burnout and firing conditions
(a) Followed by a reduction step in N2/H2, 350C, 0.3h
System
Matrix
Filler
Metallisation Burnout
[oC/h]
High-temperature cofired ceramic
IBM
Alumina
…
Molybdenum …
Low-temperature cofired ceramic
Asahi glass
Ba-Al2O3SiO2- Al2O3
…
…
B2O3
Forsterite
DuPont
Alumina silicate Al2O3
Silver, Gold 350/1
Fujitsu
Borate glass
…
Al2O3
Copper
Matsushita
0.35NaAlSi3O8…
Copper
550/4(a)
(in air)
0.65CaAl2Si2O8
Murata
BaO-B2O3....
Copper
…
Al2O3-CaO-SiO2
Narumi
CaO-Al2O3Al2O3
Silver,
…
gold(top)
B2O3-SiO2
NEC
Lead borosilicate Al2O3
Silver,
…
palladium
Shoei
BaZr(BO3)2
SiO2
Copper
600/(in air)
Taiyo Yuden
CaO-MgO…
…
Al2O3-SiO2Copper
B2O3
19.01.2011
Firing
[oC/h]
Atmosphere Shrinkage
[%]
1560/33
H2/N2
17
900/1
Air
12
850/0.3
950 to
1000/-
Air
12
.....
Reducing
.....
900/0.3
Nitrogen
950/-
Reducing
13.5
880/0.3
Air
16
13
900/980/2.5
Air
Nitrogen
12
.....
950/-
Electronic Pack….. Chapter 3 Materials and Basic Processes
Reducing
Slide 11
Ceramics, continued
Fig 3.1 e.2 Physical properties
System
Dielectric
constant
Dissipation
factor
Thermal
Conductivity
Fracture
trength
Breakdown
voltage
[MPa]
[kV/mm]
Insulation
resistance,
[Ohmcm]
Coefficient
of thermal
expansion
[10-6/°K]
[W/m°K]
>1014
6.5
16.7
275
0,001
0,002
…
>1013
0,002
0,0007
0,0003
0,003
0,003
0,001
…
1014
>1014
1014
>1014
>1013
>1014
…
3,8-6,8
7,9
4,0
6,1
8,0
5,5
7,9
1,9
7,7
5,8
…
2,9
…
2,9
4,2
2,5
…
…
3,3
6
245
206
…
245
196
196
343
137
196
245
High-temperature cofired ceramic
IBM
9.4
Low-temperature cofired ceramic
Asahi glass
DuPont
Fujitsu
Matsushita
Murata
Narumi
NEC
Shoei
Taiyo Yuden
19.01.2011
07.10.99
6.3
7.8
4.9
7.4
6.1
7.7
7.8
3.9
7.0
6.7
Electronic Pack….. Chapter 3 Materials and Basic Processes
…
40
50
20
88
…
…
…
…
Slide 12
Glasses:
• Glasses are amorphous, supercooled liquids
–Uses:
• Matrix for thick film pastes
• Hermetic seals
• Substrates, together with ceramics
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 13
Plastics
• Organic, synthetic polymer materials with numerous uses in
electronics
Table 3.3 a): Plastics in various types of electronics applications.
Integrated circuits,
Transfer moulding compounds, injection moulding
transistors,
compounds, castings, potting, dip and powder coating
diodes, and other
compounds, and die attach adhesives. Photoresists. Junction
discrete devices
coatings.
Wires and cables
Sleevings, coatings, varnishes, intermetal dielectrics.
Connectors
Transfer moulding, injection moulding, compression
moulding compounds.
Hybrids
Conductive and non conductive adhesives, sealants,
conformal coatings.
Transformers, coils,
Transfer moulding compounds, coatings, potting compounds,
bushings
coil impregnates, wire insulation.
Printed circuit boards Laminates, conformal coatings, solder masks, masking tapes,
component attachment adhesives, and vibration dampers.
Photoresists.
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 14
Plastics, continued
• Composition, properties:
–Monomers derived from benzene
19.01.2011
07.10.99
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 15
Plastics, continued
Table 3.3 b):Types of plastics for various purposes.
USE
Transfer moulding
Injection moulding
Encapsulation/casting
Adhesives
Coatings
Films
Sealants
19.01.2011
SUITABLE MATERIALS
Epoxides, silicones, phenolics, polyimides.
Polyethylene, polypropylene, polyphenylene sulphide.
Epoxides, polyurethanes, silicones.
Epoxides, polyimides, cyanoacrylates, polyesters, polyurethanes.
Silicones, fluorocarbons, epoxides, polyxylylenes, polyurethanes,
polyimides.
Polyesters, polypropylene, polystyrene, polyimides.
Silicones, polysulphides, polyurethanes, epoxide-polyamides, and fluorosilicones.
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 16
Plastics, continued
• Requirements:
–High electrical resistivity, high breakdown field,
low dielectric losses, low dielectric constant
–Thermal and mechanical stability
–Thermal expansion compatible with Si and metals
–High mechanical strength/softness and flexibility
–Chemical resistance
–Good adhesion to other materials
–Ease of processing
–Low water absorption, small changes of the
properties during the effect of moisture.
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 17
Plastics, continued
• Composition,
properties:
–Linear, branched or
crosslinked
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 18
Plastics, continued
• Thermoplastic or thermosetting
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 19
Plastics, continued
• Polymerization: A-, B-, C-stages.
• High electrical resistivity , low
dielectric constant er, low loss
factor tan , high breakdown
field Ecrit
• Poor thermal conductors
• Visco-elastic
• Fig 3.7: The structural unit of
certain monomers/polymers.
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 20
Plastics, continued
• "Glass transition": change from glass-like to rubber - like
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 21
Plastic Materials:
•
•
•
•
•
•
•
•
•
•
Epoxy
Phenolic
Polyimide
Teflon
Polyester
Silicone
Polyurethane
Parylene
Acrylic
Polysulphone, polyethersulphone, polyetherimide
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 22
Plastics, continued
• Fig. 3.9: a):The epoxide
group, which is the
building block in epoxy,
b) - e): Starting materials
for epoxy:
b): Bisphenol A, which
constitutes most of the
starting material. The Hatoms in the places X are
often replaced with Br to
reduce the flammability;
c): Epoxy novolac;
d): The hardener
dicyandiamide;
e): The catalyst.
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 23
Plastics, continued
Table 3.5:
Property
Properties of high temperature moulding plastics [3.6, page 307].
PolyPolyether PolyPolyethersulphone sulphone -phenylene
-imide
(Udel)
(Victrex) sulphide (Ryton) (Ultem)
Flexural strength
15.4
18.6
25
21
[x10-3psi]
Flexural modulus
0.39
0.37
1.7
0.48
[x10-6psi]
Tensile strength
10.2
12.2
16.2
15.2
[x10-3psi]
Dielectric constant
3.03
3.45
3.8
3.1
[1 MHz, 25oC]
Dissipation factor
0
0.008
0.0014
0.006
[1 MHz, 25oC]
Volume resistivity
50
100
45
6.7
[x10-17 Ohmm]
Electrical strength
17
16
17.7
28
[kV/mm]
Deflection temperature
174
202
243
200
[oC] at 264 psi
Thermal expansion
56
55
40
56
coefficient [ppm/oC]
Water absorption [%]
0.3
0.4
0.05
0.25
(24h)
Maximum continuous
160
170-200 170
170
temperature [oC]
Ultem +20%
glass
reinforced
30
0.9
20
3.5
0.0015*
0.7
26.5
209
25
0.26
170
* 1kHz
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 24
Basic Processes
• Description of some of the basic processes used
in microelectronics, microsystems and
electronic packaging.
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 25
Photolithography
• Fig. 3.10:The steps in
photolithographic
transfer of patterns
and the subsequent
etching of metal films
with negative
photoresist.
• If positive resist is
used, it is the
illuminated part of the
photoresist, which is
removed during the
development.
• Positive resist most
used today because of
better accuracy
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 26
Photolithography, cont
• Also, please observe the concept of straight polarity
masks and reverse polarity masks:
– Straight polarity:
In layers with straight polarity, a positive image of the layout
will be transferred onto the process layer. In other words, draw
the objects that need to be covered with photo-resist after
development.
• Openings: Mask pattern is repeated on the substrate for additive
films etc., like metal patterns. (Assuming positive resist is used)
– Reverse polarity:
In layers with reverse polarity, draw the areas where photoresist should be removed. The actual mask will be the negative
image of the layout.
• Mask pattern is oppositely repeated on the substrate for additive
films etc., like openings in oxide for later difussion of dopants.
(Assuming positive resist is used)
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 27
Screen Printing and Stencil Printing
• Fig. 3.11: Screen
printing:
a) and b): Printing
process,
c) and d): Details of the
screen
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 28
Etching
• Wet, chemical etching
• "Dry" plasma- or reactive ion etching
• Examples, wet etching:
Copper:
FeCl3 + Cu -> FeCl2 + CuCl
In addition:
FeCl3 + CuCl -> FeCl2 + CuCl2
Need organic etch resist, not good with PbSn.
Gold:
KI + I2 -> KI3 + KI (surplus)
3 KI3 + 2 Au -> 2 KAuI4 + KI
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 29
Plating
• Electrolytic plating:
–Electric current of ions in electrolyte. External
circuit needed. All separate parts of area to be
plated must be electrically contacted to
external circuit.
Example: Cu in CuSO4 /H2SO4
Reaction at anode (Cu supply):
Cu -> Cu2+ + 2eReaction at catode (substrate):
Cu2+ + 2e- -> Cu
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 30
Plating, continued
• Chemical plating:
–Takes place without external current
–Needed when insulating surfacec are to be plated
–Often preceeds electrolytic plating, to make all
needed areas electrically conductive
–Complex processes of "sensitizing", "activation"
and plating
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 31
Vacuum Deposition and Sputtering
• Vacuum
evaporation:
–Chamber
evacuated to
less than 10-6
Torr
–Resistance
heating
–Metal
evaporation
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 32
Other Methods for Deposition of
Conducting or Insulating Films
• DC Sputtering (Fig. 3.13.a)
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 33
Deposition, continued
• Radio Frequency AC Sputtering (Fig.3.13.b)
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 34
Methods for Electrical and
Mechanical Contact
• Soldering
–Wetting: (Fig. 3.14)
Young´s eq.: gls + gl cos Q = gs
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 35
Leadless soldering
• Leadless soldering replacing lead-based solder due health hazards and
environmental issues
19.01.2011
Slide 36
Soldering, continued
• Most common solder alloy:
63 % Sn / 37 % Pb (eutectic)
Melting point 183 oC
Table 3.6:
Properties of solder alloys 63 Sn:37 Pb or 60 Sn:40 Pb (weight %)
Value
Unit
Temp. [oC]
25
0.17
Electrical resistivity, 
µOhmm
100
0.32
"
Thermal conductivity, °K
25
51
W/m°K
100
49
"
24.5
ppm/°C
Thermal coeff. of expansion, 
Specific heat
46 000
J/kg°K
Modulus of elasticity, E
25
32 000
N/mm2
8.5
Density, 
g/cm3
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 37
Soldering, continued
• Fatigue: Coffin-Mansons formula:
N0.5 x gp = constant
where N is number of stress cycles, and gp is the
relative deformation amplitude, meaning that both
number of cycles and stress level determine lifetime
• Useful adition : 2 % Ag (Surface mount), to
reduce leaching (dissolution of the termination metal
that leads to deterioration of mechanical and
electrical properties)
• Harmful contaminant: Au, will increase brittleness
because of AuSn intermetallics
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 38
Soldering, continued
• Fig.3.15: Behaviour of solder metal at different
temperatures, schematically. [W. Engelmaier].
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 39
Soldering, continued
• Fig. 3.16:
Solder joint
fatigue in
surface
mounted
assemblies is
often caused
by power
cycling.
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 40
Soldering, continued
• Fig. 3.17: Experimental data for fatigue in Sn/Pb solder fillet
by cyclical mechanical stress. High temperature and low
cycling frequency gives the fastest failure, because the grain
structure relaxes most and is damaged
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 41
Soldering, continued
• Fig. 3.18. a) Left: Dissolution rate of Ag in solder metal, and in solder metal
with 2 % Ag, as function of temperature
b) Right: Dissolution rate of various metals in solder alloy
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 42
Soldering, continued
Table 3.7: Alloys for soft soldering [3.11]
Alloy System
Code
Melting
[mass%]
Temperature [°C]
Sn
100
63
60
50
40
10
5
Pb
62
10
5
96,5
95
36
88
93,5
37
42
15
34
43
19.01.2011
Ag
Sb In
Bi
Sn
Sn63
Sn60
Sn50
Sn40
37
40
50
60
90
95
2
2
1,5
3,5
Sn62
5
40
50
37
33
42
43
Solid
232
183
183
183
183
275
310
60
50
25
58
52
24
14
Liquid
183
188
216
234
302
314
Shear Strength
at 1 mm min-1 [Nmm-2]
20°C 100°C
22,1
19,0
33,6
21,6
30,0
24,0
34,3
13,7
28,9
14,7
179
268
296
Ag3,5 221
Sb5
236
In60
174
In50
180
In25
138
179
299
301
221
243
185
209
138
43,0
23,8
37,7
37,2
-
18,6
15,7
22,5
21,1
-
Bi58
Bi52
Bi24
Bi14
139
96
146
163
50,0
34,3
-
19,5
17,5
-
139
96
100
143
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 43
Soldering, continued
• Flux and cleaning
–Purpose of flux:
• Dissolve and remove oxides etc.
• Protect surface
• Improve wetting
–Categories:
• Soluble in organic liquids
• Water soluble
–Types:
• Organic resin fluxes ("rosin")
• Organic non resin based fluxes
• Inorganic fluxes
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 44
Soldering: Flux and cleaning
• Fig. 3.19: Time for solder alloy to wet a pure Cu surface, depending on the
activation of the solder flux. The degree of activation is given by the
concentration of Cl- ions in the flux (temperature: 230 °C)
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 45
Soldering: Flux and Cleaning
• Designations:
– R (Rosin, non-activated): No clorine added.
– RMA (Rosin mildly activated): < 0.5 % Cl
– RA (Rosin, activated): > 0.5 % Cl
• Cleaning
– Freon (TCTFE) now forbidden. Replaced by alcohol etc.
– Trend: No cleaning
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 46
Gluing
• Purposes:
–Mechanical assembly
–Electrical contact
–Thermal contact
• Materials: polymers:
–Epoxy, acrylic, phenolic, polyimide
–Metal particles for electrical conductivity:
r = 1 - 10 x 10 -6 ohm m
–Metal or ceramic particles for thermal
conductivity:
K ≈ 1 - 3 W /m x oC
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 47
Gluing, continued
• Fig. 3.20: Thermal conductivity of epoxy adhesive with various amounts of
Ag [3.16 a)]. The concentration is in volume % Ag. (23 vol. % corresponds
to approximately 80 weight %).
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 48
Gluing, continued
• Fig. 3.21: The thermal
resistance from the
electronically active
part, on top of the Si
chip (¨junction¨)
through a bonding
layer of glue or soft
solder and a thin
alumina ceramic layer
covered with Cu to
heat sink. The samples
with chips bonded by
gluing, C and A, have
approximately twice as
high total thermal
resistance as those
which are soft
soldered, D and B.
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 49
Chip Mounting: Die Bonding
• Fig. 3.22: Thermal resistance from junction to heat sink through adhesive of
various thicknesses. For thick layers the resistance approaches the value
calculated, based on the bulk thermal conductivity of the adhesive. For thin
layers the resistance is higher, approaching a constant value, which
indicates an "interface thermal resistance" caused by defects in the adhesive
layer
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 50
Chip Mounting: Die Bonding, continued
• Eutectic die
bonding:
– Au/Si (363 oC),
Au/Sn (280 oC)
• Soft soldering:
Sn/Pb, Ag/Pb
• Glueing
• Adhesive cracking, fig. 3.23: Thermal cycling
induces defects giving increased thermal
resistance.
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 51
Chip Mounting: Die Bonding, continued
• Fig. 3.24: Use of adhesive for
contacting IC-chips with
small pitch, schematically:
a): Anisotropic conductive
adhesive, the conduction is
through the metal particles
in the adhesive;
b): Electrically insulating
adhesive, the conduction is
through point contacts where
the adhesive has been
squeezed out.
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 52
Si Chip Electrical Contact
• Wire bonding
• Tape Automated Bonding (TAB)
• Flip chip
• Planar bonding
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 53
Wire Bonding
• Ultrasonic
• Thermocompression
• Thermosonic
• Geometry Types
–Ball - wedge:
Shown in
illustration
–Wedge - wedge
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 54
Wire Bonding
From Small Precision Tools
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 55
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 56
Tape Automated Bonding (TAB)
• Connection made in two
steps:
– Inner Lead Bonding
• Connecting tape to chip
– Outer Lead Bonding
• Connecting tape to substrate
• Connection made by
thermocompression
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 57
Tape Automated Bonding (TAB)
• Standard process:
– Fabrication of gold
bumps (Fig. 3.28):
• Deposition of
contact/barrier
metals
• Photolithography
• Electroplating
• Strip and etch
barrier metals
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 58
TAB, continued
• Fig. 3.26: A picture of a TAB film with the Cu pattern, as well as the holes
in the film for excising the circuits, and the sprocket holes for moving the
film during processing.
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 59
TAB, continued
• Fig. 3.27:
The main steps in
TAB processing.
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 60
Tape Automated Bonding (TAB)
• Wafer cutting
• Fabrication of TAB film
–Hole punching
–Cu foil lamination
–Lithography + etch of Cu pattern
–Tinning of Cu
• Inner lead bonding (ILB)
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 61
TAB, continued
• Protection (glob top)
• Testing
• Outer lead bonding:
–Excising, lead
bending
–Placement/thermode
soldering
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 62
Advantages of TAB:
• High packaging density
• Can contact chips with >1000 I/O
• Excellent electrical properties (high frequency)
• Robust mounting
• Pre-testable (contrary to COB)
• Gold bumps give hermetic seal to chip
• Gang bonding gives high yield, is less time
consuming than wirebonding
• TAB film can be used as daughter board
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 63
Disadvantages of TAB:
• Non-standard wafer processes
• Special custom design film for chip
• Needs special machine/tool for OLB
• Demanding repair
• Low availability of std. chips and TAB
service
• Little standardization
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 64
Flip chip
• Active face of chip is flipped towards substrate
– Substrate pads are identical to chip pads
•
•
•
•
Area array connections possible
All connections done simultaneously
Smallest possible footprint (1:1)
Short interconnections
– Low inductance and resistance
– Excellent electrical properties
• Little flexibility
– Change of chip pad configuration implies redesign of
substrate
• Small, but increasing amount of interconnections
are flip chip
• To be dealt with in much more detail…
19.01.2011
Flip Chip
• Process:
–Deposit barrier metals
–Deposit solder bump metals (solder) by
photolithography/metal mask and sputter or
plating
–Reflow
–Cut wafer
–Turn chip and mount on substrate
–Heat substrate to reflow solder
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 66
Flip Chip, history
• Introduced by IBM 1962
• Flip chip has been used for decades, but with little
impact
– Wire bonding is far more common
– Flip chip technology has not been considered mature
– The industrial infrastructure has been small
• The market share of flip chip connections is believed to
increase significantly
– Wire bonding will remain dominating for many years
• Flip chip especially for ”advanced packaging”
19.01.2011
Flip Chip, continued
• Advantages:
–Highest packing density
–Excellent hi freq. properties
–Up to 10 000 I/O
• Disadvantages:
–Very difficult placement and reliable
solder/cleaning
–Lack of thermal flexibility
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 68
Flip Chip consists of:
• Chip
– Si, GaAs, etc.
• Substrate
– Ceramic, organic,
dielectic-covered metal,
silicon, etc.
• Interconnection system:
– Metallization on chip and substrate pads
– Chip (or substrate) bumps
– Bonding material
– Underfill encapsulant
19.01.2011
Different Flip Chip technologies
• Flip chip is not standardized!
19.01.2011
From C. Lee, ESTC 2006, Dresden
Wire Bonding, TAB and Flip Chip
Comparison of wire bonding, TAB, and flip chip soldering [3.22]
Table 3.8:
Bonding technology
Wire Bond
TAB
Flip-Chip
Material(s)
Al
Au
Cu
Pb-Sn
Melting temperature [°C] 660
1064
1084
310
Bonding geometry
25 µm diameter
25x100 µm tape 125 µm diameter
x 2,5 mm length
x 2,5 mm length
100 µm height
Typical pitch [µm]
170 µm perimeter 200µm perimeter
250 µm area
Minimum Pitch [µm]
60 µm perimeter
70 µm perimeter
50 µm area
Strength per bond [gram] 6
10
50
30
Lead resistance [mOhm] 142
122
17
1,2
Interlead capacitance [pF] 0,025
0,025
0,006
<0,001
Lead inductance [nH]
2,6
2,6
2,1
<0,2
Thermal resistance
[°C/mW] per bond
80
52
8
0,5
No. of I/Os per chip
Typical pitch
8 mm chip size
184
160
1024
Minimum pitch
8 mm chip size
266
400
15150
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 71
Planar Bonding with Adaptive Routing
• Fig. 3.32: Planar bonding
with laser-assisted
adaptive conductor
routing.
The top two figures a)
and b) show a substrate
cross section with details
of the mounting of the
chip in an etched
through-hole.
Figure c) shows the
conductor layers and
polyimide insulation on
top of the substrate. The
bottom figures show an
exploded view of all the
layers.
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 72
End of Chapter 3
Materials and Basic Processes
•Important issues:
– Materials:
• Distinguish between metals, ceramics, glasses and plastics
– Important mechanical and thermal parameters like modulus of eleasticity,
thermal expansion coefficient and thermal conductivity.
– Important electrical parameters like dielectric constant and resistivity or
conductivity
– Have a basic understand of the importance and value of the most important
materials parameter, and why they are important for the use of the specific
material in specific applications.
– For instance knowing the electrical conductivity of copper or thermal
conductivity of epoxy within an accuracy of 25%
– Basic processes
• Lithographics, screen and stencil printing, etching, plating, vacuum
deposition, sputtering, soldering, gluing, wire bonding, TAB, and flip chip
– Other basic processes described in other chapters, like surface mount technology
•Questions and discussions?
19.01.2011
Electronic Pack….. Chapter 3 Materials and Basic Processes
Slide 73