Passive Electronic Components
Lecture 3
Page 1 of 19
10-Jun-2015
Mounting of Passives Electronic Components
Lecture Plan
1.
2.
3.
4.
5.
6.
Point-to-Point Mounting
Through-Hole Mount Technology (TMT).
Surface Mount Technology (SMT).
Printed Circuit Board (PCB).
Soldering.
Gluing and welding.
Development of Mounting Technique in Electronics
Point-to-Point Mounting
Through-Hole Mounting
Surface Mounting
1. Point-to-Point Mounting
The technology is characterized by:
 type of component terminals: (a) wire, (b) lug, (c) clamp, (d) plug;
 component mounting by: (a) screwing, (b) clamping, (c) soldering to lugs, (d) insertion in
a socket;
 interconnections are performed using: (a) hook-up wire, (b) chassis.
Point-to-Point Mounting technology started together with the first electrical and electronic appliances.
Fig.1. Point-to-Point Mounting
Lug
(variable resistor)
Clamp
(capacitor)
Wire
(resistor)
Plug
(vacuum tube)
Fig.2. Different types of terminals in electronic components suitable for point-to point mounting
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Method of soldering in the case of Point-to-Point Mounting is manual soldering using soldering iron.
2. Through-Hole Mount Technology (TMT) is the method of mounting of electronic
components with wire or wire-like stamped terminals by insertion of terminals in
special holes in printed circuit board followed by soldering of the terminals to metalizes
pads that surround the mounting holes.
The technology is characterized by:
 Needle-like (wire or stamped) terminals of the components;
 Dielectric panel with holes (printed circuit board, PCB);
 Mounting pads around the holes and interconnections between the pads formed from
copper foil laminated to surface of dielectric panel;
 Components mounting by insertion of wire terminals through the holes in PCB;
 Wave Soldering Technology.
Dielectric panel and copper foil patterns laminated to its surface constitute Printed Circuit
Board (PCB). Through-Hole Mount Technology is inseparably linked with PCB.
a
b
Fig.3. Cross-section of PCB with through-hole mounted components (a).
Top view on PCB with mounted components (b).
Bottom view on PCB – "printed" copper conductors (c).
2.1. PCB history. http://www.pcfab.com/history.htm
2.1.1. In 1903, Albert Hanson, a Berliner living in London, filed a “printed” wire
patent aimed at solving the telephone exchange need. It was proposed to
produce conductive metal patterns by cutting or stamping of copper or brass
foil. Then the patterns were bonded to dielectric plate (additive patterning).
2.1.2. Thomas Edison proposed idea of selective applying of glue and dusting of
conductive (graphite or bronze) powder.
2.1.3. In 1913, Arthur Belly filed for a patent describing the method in which metal
was etched away (subtractive patterning). Resists layer had to be applied to
metalized surface of the board before etching in places where metallization has
to remain.
2.1.4. In 1918, Max Schoop proposed flame-spraying process.
c
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2.1.5. In 1942 newly invented in England bomb fuse had printed circuit instead of
wiring.
2.1.6. In 1947, “A Circuit Symposium” conference in Washington, D.C. sponsored by
U.S. Aeronautical board and the NBS was held. Six processes were endorsed by
the governmental technical representatives:






Painting by metal-filled inks.
Metal spraying.
Chemical deposition.
Vacuum deposition.
Die stamping and bonding.
Dusting conductive powder on tacky ink.
Subtractive patterning process that nowadays has become the principal process of PCB
technology was not mentioned. It was supposed to be an auxiliary process.
2.1.7. In 1948 the U.S. authorities ruled that all electronic circuits for airborne
instruments were to be printed.
2.1.8. In the 50s photoimaging and etching processes were introduced together with
copper-clad material in PCB manufacturing. These improvements were
connected with name of inventor Paul Eisler, Austrian Jew that was forced out
of work by the fascists in 1934 and left for England.
In the beginning the components were inserted in PCB manually. Later semiautomatic and
even automatic insertion equipment and solderwave soldering equipment were developed.
Nowadays TMT remains in use in some limited applications in the form of mixed technology
(TMT + SMT). It is used in some products that should not be miniaturized (TV, videos, home
audio, etc.). The reason is a cost consideration. Semiautomatic TMT equipment has typical
insertion rate of 750 cph (components per hour). Automatic equipment can reach about 15,000
cph speed but needs special pre-process: terminals forming and components taping in special
sequencer machine.
Typical method of soldering in TMT process is wave soldering technology (see “Soldering”
paragraph below).
3. Surface Mount Technology (SMT) is the method of mounting of electronic
components on flat surface of PCB without mounting holes.
The technology is characterized by the following features:
 Stamped “legs” in so called leaded component or metallized edges of so called leadless
component (chips) constitute the terminals (see picture below).
 Component placement on PCB and soldering are completely automated.
 PCB is similar to TMT PCB but without mounting holes.
a
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Fig.4. Surface mounted components on PCB
In the early 80s the industry began to replace the traditional Through-Hole Mounting technique
(TMT) with the Surface Mount Technology (SMT). Special Surface Mountable Devices (SMD)
replaced the traditional wire-leaded components. The historical roots of SMT can be traced back
to the middle of 70-s when hybrid and microwave circuits were developed on the base of so
called “leadless components” mounted on ceramic substrates with screen printed
interconnections.
SMT components may be leaded and leadless (chips). They are placed on PCB by pick-and-place
machine (Chip Shooter) with placement rate up to 40,000 cph. Placement precision is about 0.05
mm at 3. The outline dimensions of a smallest two-terminal chip component are
0.3mm×0.15mm. Fine pitch multi-terminal components (ICs) have a pitch down to 0.3 mm.
Advantages of SMT components (when compared with TMT components):
 Smaller dimensions of components make it possible to increase mounting density.
 Smaller dimensions of components result in better HF performance (low parasitic
inductance, low package propagation delay, low electromagnetic interferences).
 SMT components commonly have lower cost.
Problems related to SMT components:
 Rigid terminals of leadless chips make solder joints more prone to cracks that may
result from PCB bending or vibrating.
 Rigid terminals of leadless chips make solder joints more prone to cracks that may
occur when PCB assembly is subjected to temperature cycling. The phenomena is
called thermal fatigue and results from mismatch of component's and PCB's thermal
coefficients of expansion (TCE).
 “Tombstone effect” (see the end of the lecture) is possible during soldering of chip
components.
 Labeling (marking) of small components is problematic or even impossible.
Thermal fatigue of solder joints .
Material fatigue is a structural damage suffered by materials when they are subjected to periodic
mechanical stress. The periodic stress may result from:
 application of periodic mechanical force;
 temperature cycling and mismatch of component's and PCB's thermal coefficients of
expansion.
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We shall consider the last case.
Suppose that a chip resistor having length d is soldered to the surface of a PCB as it is shown in the
figure below. The solder layer thickness is  . Ambient temperature is T1.
d
T1
PCB
Chip resistor
1
δ
Solder

Suppose that ambient temperature changed to T2 : T2  T1  T . Even in case when chip resistor does
not dissipate power a shear strain in the solder joint arises because of different thermal coefficients of
expansion of chip and PCB.
Material
Alumina (chip resistor substrate)
Epoxy glass FR4 (PCB material)
Thermal coefficient of
expansion (TCE)
1 = 6 ppm/C
 = 18 ppm/C
Chip length after temperature change will be d 1  1T  . At that, the length of underlying part of
PCB will be d 1  T  . It will result in shear stress in the solder blocks. Suppose that the angle
between adjacent sides of each of two solder blocks shown in the above picture was 90 at ambient
temperature is T1. It is known from the Strength of Materials that shear strain is measured by the angle
 p that represents the change of the initially right angle as shown in below picture (  p  0 when
ambient temperature is T1).
T2
p
1

Commonly this angle is very small and therefore may be approximately replaced by its tangent:
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

 p  tan  p 
 1    T  d
.
2
(1.1)
Multiple (cyclic) deformation of solder joint results in its cracking (Fatigue Phenomenon).
The first-order approximation of the relationship between the strain  p in soldering material
and number of cycles to the material failure N f is given by Coffin-Manson relation:
1   p
Nf  
2  2 f
1
c
 ,


(1.2)
where  f - fatigue ductility coefficient, c - fatigue ductility exponent. They are two dimensionless
physical constants that characterize particular soldering material.
Equation (1.2) is applicable to Low Cycle Fatigue - the loading that typically causes failure in less
than 104 cycles and is associated with relatively large plastic (non-elastic) strain in metals. This
situation is typical for solder joints. Equation (1.2) may be represented graphically as a straight line in
coordinates log  p , log N f  (see graph below).
Plotted experimental data for 60Sn40Pb solder
Let us substitute  p in (2) by (1):
1
1
 c
4 f  
1      T  d  c 1 
 .
Nf   1
 


2 
4 f  
2





T

d
1



In the case of 60Sn40Pb solder it may be supposed that  f  0.33 , c  0.5 .
For lead-free Sn3.0Ag0.5Cu solder  f  0.325 , c  0.57 [4].
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Numerical example. Suppose that d = 6.310-3 m (the biggest size of standard chip resistor), T =
35 K,  = 510-5 m (common thickness of solder in a joint). Number of cycles to failure may be
calculated as the following.
d = 6.310-3 m
T = 35 K;
 = 510-5 m
 = 18 ppm/K=
=1810-6 1/K;
1 = 6 ppm/K=
=610-6 1/K;
 f  0.33 ;
1
c
1      T  d 
Nf   1

2 
4 f  

6
3
1  18  6  10  35  6.3  10 

N f  

2
4  0.33  5  10 5


1
0.5
 3  102
 1 K   K  m 
 1

m


c  0.5
Nf - ?
Pay attention that the power of -2 = -1/0.5 is not integer value! It is approximate value with
single significant digit.
4. Printed Circuit Board.
4.1. PCB construction and parameters
Boards are generally defined by:
 type of dielectric material,
 number of conductor layers,
 copper thickness that is traditionally characterized by “copper weight”.
Copper Weight is measured in Ounces of Copper Per Square Foot (m = 1oz.= 28.35g, S = 1ft2 =
0.3052m2). The common range of the parameter is 1/4… 3 oz. Typical value is 1 oz. Higher numbers
are used in high current and high frequency applications.
Copper density is = 8920 kg/m3. Let us calculate 1 oz. copper layer thickness h.
Suppose that copper weight number has unlimited precision (idealization):
m = 1oz. 28.35g = 0.02835 kg
S = 1ft2  0.3052m2
 = 8920 kg/m3
m  Sh;
h
m
S
h
0.02835
 34.2  10 6 (m)
2
8920  0.305
kg
m
kg m 3  m 2


h=?
It is commonly supposed that 1 oz. of copper per square foot corresponds to 35 m of copper
thickness.
Let us calculate so called sheet resistivity of 1 oz. copper layer. Sheet resistivity is resistivity of a
square pattern of a film or a foil of given thickness. Resistance of rectangular pattern may be
calculated as the following:
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Lecture 3
R
Page 8 of 19
l
l
 l

  ,
S
hb h b
where l, b, h, S – respectively length, width, thickness [m], and cross section area [m2] (perpendicular
to the length direction) of the pattern,  - material resistivity [m]. Conclusion: Resistance of a
PCB foil pattern depends on its length/width ratio and does not depend on absolute values of its
linear outline dimensions.
Suppose that l  b (square pattern). Its resistance we shall call “sheet resistivity” and designate as .
h = 3510-6 m
 = 1.710-8 m
l b
=?
R
l
l



S
hb h
  1.7  10 8   m 35  10 6 m  0.50  10 3  sq
Sheet resistivity  =  h . It must have [] dimensions. But for better understanding of the matter it is
commonly designated as [/square] or [/□].
Layering
Layers of copper traces in PCB are divided by dielectric layers. Number of copper layers may vary
from 1 to 30. External layers (top and bottom) are covered by a screen printed solder mask.
Commonly board thickness is 15 mil…250 mil (1 mil=25.4 m) or 0.38 mm…6.35 mm.
Dielectric thickness is 1.3…2 mil or 0.03 mm…0.05 mm.
Line width and spacing between lines – down to 5 mil or 0.13 mm. Line (trace) thickness and width
are selected depending on the expected current. Spacing between the traces depends on the expected
voltage.
Vias (metallized holes for interlayer connections).
Types: (a) blind, (b) through hole, (c) buried, (see picture below).
a)
b)
c)
a)
Vias: a) blind ; b) through hole; c) buried www.morris.com.au/technical/ art_bb.htm
4.2. Dielectrics for PCB manufacturing
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Glass-reinforced polymer (magnified cross-section)
Dielectric
materials for PCB
manufacturing
Glass-reinforced
polymer
laminates
Ceramics
Co-fired
ceramics
Thick-film
multilayer (TML)
High
temperature
(HTCC)
Lowtemperature
(LTCC)
Glass-reinforced polymer laminates. The most common combination of resin and reinforcement
material is epoxy and woven glass (FR-4, FR-5). In special applications another materials are used like
polyester resin, non-woven glass, etc.
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Ceramic PCBs .
Three ceramic based technologies are used to manufacture ceramic PCB: Thick Film Multilayer
(TFM), High Temperature Co-fired Ceramic (HTCC) and Low Temperature Co-fired Ceramic
(LTCC). The same technologies are used for manufacturing of Multi-Chip Modules (MCM).
Thick Film Multilayer (TFM). Multilayer circuits formed by sequential screen printing of conducting
and dielectric thick-film materials, their drying, and firing. Double-sided and multilayer circuits with
up to four circuit layers are manufactured in high volume for commercial applications (automotive,
telecommunications). For military and aerospace applications, circuits with six to eight circuit layers
are manufactured in moderate volume.
Co-fired ceramics (HTCC and LTCC). Sheet dielectric materials are cast as a tape. All layers are
screen-printed by conductive thick-film ink in parallel. Printed layers are laminated (stacked and
pressed together), and then co-fired. The advantage of co-firing process is possibility of inspection of
all printed layers prior to lamination. This insures better capability of the process compared to
sequential screen printing of multilayer circuits.
High Temperature Co-fired Ceramic (HTCC). Ceramic tape material is commonly based on
alumina. It is fired at 1600…1800 C in hydrogen atmosphere. Only tungsten (W) and
molybdenum (Mo) can be used as conductors because of the high firing temperature.
Unfortunately their electrical conductivity is significantly lower when compared to silver.
Low Temperature Co-fired Ceramic (LTCC). The tape material is composed of a glass and alumina.
High conductivity silver-based thick-film material is used for screen printing of conductive traces.
Multilayer PCBs with 50 or more layers have been manufactured using LTCC technology. This
technology is well-suited for constructing RF modules for wireless applications with capacitors and
inductors integrated into the substrate.
Thermal conductivity of PCB materials
Material
Thermal conductivity, W/(mK)
FR4
0.25
LTCC
2.5…4
HTCC
16…30 (Al2O3)
180 (AlN)
260 (BeO)
Copper
401
5. Soldering.
Permanent connection of mechanical parts may be done by using welding, soldering, and gluing. Their
essence is introduction of liquid phase between the parts to be connected (molten base metal in
welding, molten solder in soldering, glue in gluing). The liquid wets the parts, gets in intimate
interfacial contact with them arising intermolecular attractive forces. Then the liquid solidifies keeping
the parts connected.
Liquid
Part 1
Part 2
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Soldering is a process by which the parts are joined together using material (solder) with lower
melting point than melting points of materials of joined parts. Welding is performed by melting
of materials of joined parts. Glues are liquid materials that solidify as the result of chemical
reaction or evaporation of solvent.
5.1. Soldering materials.
Soldering
materials
Soft solders
Leadcontaining
Glass
Hard solders
(for brazing)
Lead-free
Solder is metal (elemental or alloy) or glass. Glass is used, for example, to attach optic cable to
metal connector or to assemble ceramic and metallic parts of hermetic IC package.
Metallic solders may be split in two families:

Hard solders are copper, zinc or silver alloys with melting temperature above 400C.
High melting temperature makes them not suitable for electronic assembly.

Soft solders have lower melting temperature (but lower mechanical strength) when
compared to hard solders. The most of soft solders are tin alloys.
Tin is unique metal that wets vast majority of the metals. Six not wetted by tin (and therefore
not solderable by tin alloys) metals are:






Cast iron,
Chromium (Cr),
Titanium (Ti),
Tantalum (Ta),
Magnesium (Mg),
Beryllium (Be).
The fact that some metals that are not wetted by solder is important. These metals are used in
soldering machinery for manufacturing machine parts that get in touch with molten solder.
Lead-containing solders. They were basic solders in electronic industry for many years. They
have relatively low melting temperature, excellent mechanical properties but comprise toxic lead.
Nowadays they are gradually replaced by lead-free solders.
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The most commonly used tin-lead alloys (currently they are used mostly in military and aerospace
applications).
Alloy
Melting range,
C
Comments
Sn63Pb37
183
The alloy is eutectic. It is used when temperature limitations are
critical and in applications where an extremely short melting range
is required.
Sn62Pb36Ag2
178-190
The alloy is used for electronic assembly.
Lead-free solders.
The most frequently used lead-free solders are composed of 3…4% of silver, 0.5…0.7% of
copper, and tin (the rest). This family of solders is commonly called SAC (Sn, Ag, Cu)
solders. Melting point of respective eutectic ternary alloy is 217C (34 higher than melting
point of eutectic tin-lead alloy).
The most commonly used SAC alloy is Sn-3.5Ag-0.75Cu.
Alloy
Melting range,
C
Sn-3.5Ag-0.75Cu
218
Comments
The alloy is eutectic.
Issues with lead-free solder (when compared with Sn63Pb37 solder).
Higher melting point of lead free solder (217C versus 183C) pushes peak reflow temperatures from
220C to 260C. It results in:
1.
2.
3.
4.
5.
Energy consumption increase and impact on the ambiance.
Total product cost increase. (More expensive solder, higher energy spending).
More rigorous requirements to soldered components. (They are exposed to higher temperature).
More rigorous requirements to fluxes.
Higher probability of fatigue cracks in solder joints.
5.2. Fluxes. Commonly wetting of the surfaces of soldered parts by molten solder is
limited by oxides and contaminations. Fluxes are special materials that remove oxide
film and contaminations from soldered parts and prevent further formation of oxide
films during soldering process. Furthermore, the fluxes lower the surface tension of
the solder and promote wetting. In the past flux residues had to be removed after
soldering in the most cases. Modern “no-clean” fluxes do not require removal of flux
residues.
5.3. Wave soldering. The process is commonly used for soldering of through-hole
mounted components to PCB. Sometimes it is used for soldering SMT components.
But they have to be glued to PCB in advance. The basic equipment is a wave
soldering machine. It comprises conveyor that moves the PCBs with inserted
components through three different zones: (a) fluxing, (b) preheating, (c) soldering
(see picture below). Soldering is performed by “solder wave” device. It is a pan of
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solder equipped with a pump that produces the actual wave of molten solder (see
picture below).
Wave soldering machine
Solder wave
5.4. Reflow soldering. It is the most commonly used process for soldering of surface
mounted components. The process is based on using special paste containing both
flux and solder. The solder paste is usually stencil printed onto a circuit board at
appropriate points. Then surface mount component are placed on the paste patterns.
The board with components is run through “reflow oven”. Solder in paste melts and
form the joints between the terminals and PCB.
Stages of SMT soldering:




Solder paste printing or dispensing.
Components placement.
Soldering.
Cleaning (except of “no-clean” soldering materials).
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Stencil
Stencil printer
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Chip shooter
5.5. Solderability. The surfaces of component terminals that have to be soldered to PCB
are coated by thin solder layer by components manufacturer. It must keep for a long
time (at least more than a year) ability to be easily wetted by molten solder. This
ability is called solderability and can be measured using special tests. For example in
”Dip and Look Test” a component (or its terminal only) is dipped in flux and after
that in melted solder heated up to the specified temperature. Then the terminal area
that has been dipped in solder is evaluated. Commonly more than 95% of entire
critical terminal area must be newly covered by solder.
Solderability problems.
Non-wetting. Contamination, oxidation, diffusion processes in terminal may reduce its solderability.
It means that some percentage of the terminal surface will not be wetted by solder. As a result of it
electrical contact may be non-reliable and/or solder joint strength may suffer.
Leaching. Leaching is dissolution of base metallization of chip terminal in molten solder. It happens
when base metallization is a film of metal that easily dissolves in molten solder (silver, gold, etc.) and
protective (barrier) nickel coating is damaged or missing.
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Tombstone is a chip component that has flipped to a vertical position during reflow soldering. The
phenomenon is caused by an unequal wetting of its both terminals. The surface tension in the terminal
where solder melted early, forces the component to stand up on its end.
The unequal wetting may be caused by (a) wrong solder pad design, (b) bad solderability of terminal,
(c) unequal amount of solder paste under the terminals, (d) unequal temperature of the terminals. To
reduce the temperature gradients, the rate of temperature rise in pre-heat zone of reflow oven must be
reduced. The soak time should be prolonged. The use of nitrogen in reflow soldering can increase the
tomb stoning effect due to a higher surface tension of the melted solder in nitrogen atmosphere.
Tombstone model
It is supposed that termination from left side is disconnected for some reason. The following forces are
taken into account:
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 surface tension in solder fillet at the face side of right termination;
 surface tension of solder under right termination;
 weight P of the part.
Solder surface area change after clockwise rotation of the part around its right lower corner.
Angle of rotation is  .
Solder surface area S  reduction in solder fillet at the face side of right termination:
1
S   HW  2   H 2 .
(2.1)
2
Solder surface area increase S  under right termination:
1
S   AW  2   A 2 .
(2.2)
2
Resulting solder surface area change:


S  S   S   W  A  H    A 2  H 2 .
(2.3)
Potential energy change:
1
E  S    A  H W  A  H   LP,
(2.4)
2
where  is surface tension of molten solder. Surface tension of tin/lead solder is about 0.4 mN/mm.
Surface tension of lead-free solder is about 0.5 mN/mm.
Positive energy change means that the chip initially was in position with minimal potential
energy, i.e. in stable position. Negative energy change means that the chip initially was in
position with maximal potential energy, i.e. in instable position when tombstoning is possible.
d E 
1
   A  H W  A  H   LP.
d
2
(2.5)
For 60Sn/40Pb solder surface tension at 235C and with normal electronic-grade flux is
d E 
0.4 mN/mm = 0.4 N/m = 0.4 J/m2. Initial data for standard chip resistors and
calculation
d
results according to (2.5) are presented in the table below.
Case
0201
0402
0603
0805
1206
1210
1218
2010
2512
Chip
length
L, mm
Terminal
length A,
mm
Chip
thickness
H, mm
Chip
width
W, mm
Chip
weight, mN
0.60
1.00
1.55
2.00
3.20
3.20
3.20
5.00
6.30
0.10
0.25
0.30
0.30
0.45
0.45
0.45
0.60
0.60
0.23
0.35
0.45
0.45
0.55
0.55
0.55
0.60
0.60
0.30
0.50
0.85
1.25
1.60
2.50
4.60
2.50
3.15
0.0015
0.008
0.02
0.04
0.10
0.16
0.27
0.27
0.45
d E 
,
d
mNmm
-0.032
-0.040
-0.081
-0.080
0.056
0.116
0.208
0.675
1.418
Passive Electronic Components
Lecture 3
Page 18 of 19
Analysis of equation (2.5) gives direction to decrease tombstone probability: to decrease parameters
 , H. This means to use solders with lower surface tension, to decrease height of the component or to
exclude at all metallization on face side of the terminal.
Skewing is misalignment of a part regarding its target position. It may be caused by an unequal
wetting of both terminals. The surface tension in the terminal where solder melted early, makes the
component to skew.
6. Gluing and welding.
Gluing. The alternative method of component mounting on PCB is gluing by conductive adhesives.
The conductive adhesives can be screened or dispensed onto the circuit board surface prior to placing
a component onto the board in the same manner as solder paste. There are two kinds of adhesives: (a)
silver filled, (b) gold filled. The advantages of conductive adhesive when compared with solder are:

Lower curing temperature 120…150C (versus 220…260C soldering temperature);

Better withstanding to thermal cycling;

No softening at high temperatures
The disadvantage is higher contact resistance that may be unstable when adhesive is used with nonnoble metallization of terminals [3]. Typical contact resistance of soldered connection is 10…15m.
Modern conductive adhesive has contact resistance less than 50 m [1]. The newest types of glues are
reported to be usable with standard tin plated terminals [3]. The examples are POLYSOLDER
manufactured by Cookson Electronics or ABLESTIK ICP-3535M1 manufactured by Henkel
Electronic Materials.
Welding. The technique that is called wire-bonding is used in electronic assembly (preferably in
hybrid modules assembly) and for interconnections in component assembly. The connections are made
using ultrasonic energy and metal wire. Wire types:

Gold (Au) with diameter 18…50m,

Aluminum (Al) with diameter 25…50m.
Passive Electronic Components
Lecture 3
Page 19 of 19
Literature.
1. King-Ning Tu. Solder Joint Technology: Materials, Properties, and Reliability. Springer.
2007, 373 p.
2. Rudolf Strauss. SMT Soldering Handbook Second Edition. Newnes, 1998, 371 p.
3. Dreezen G., Deckx E., Luyckx G. Solder alternative: Electrically conductive adhesives
with stable contact resistance in combination with non-noble metallization. CARTS
Europe 2003, pp.223-227.
4. Nathan Blattau and Craig Hillman A Comparison of the Isothermal Fatigue Behavior
of Sn-Ag-Cu to Sn-Pb Solder. DfR Solutions, College Park, Maryland.
http://www.dfrsolutions.com/pdfs/2006_Blattau_IPC.pdf