“Soldering and Brazing”
comparing with
Diffusion bonding, Hot pressing,
and Solid phase bonding
Dr. Kunio TAKAHASHI
- Associate professor,
Dept. of International Development Engineering,
Tokyo Institute of Technology,Tokyo 152-8552, Japan
Phone/Fax:+81-3-5734-3915
E-Mail:takahak@ide.titech.ac.jp
http://www.ide.titech.ac.jp/~takahak/
Prior to this lecture...
Activities of Japanese welding community

Organizations and their roles

Japanese system of education and certification

Movement around Asian Welding Federation
About lecturer’s ...

Back ground
welding ( what is this ? )

Tokyo Institute of technology
http://www.titech.ac.jp/

Department of International Development Eng.
Network beyond the border of
(community)
engineering field
nation
http://www.ide.titech.ac.jp/
Welcome to Japan
Already, you have joined to our Network.
Welding Technology,
as ”Inter-Field” Engineering
based on







Plasma physics
Electronics/Electrical Eng.
Control (“self-controlled” is the best)
Thermal Eng.
Fluid dynamics
Steels
Material science
(Materials)
Fracture mechanics
- Making
- Design
Physics of phenomena
Standard
roles of Society
Power Source
= Heat sources





Plasma
e--beam
Laser
Joule’s heat
etc…
Industry
About this lecture “Brazing and Soldering …”

Basic knowledge based on physics
– Phenomena
– Comparison with other welding processes
– What is and what is not clarified, theoretically ?
– Recent progresses for physical understanding.
so,

You will understand...
– Why and How the process is used ?
– How the process can be modified ?
Experimental training
Contents of
this lecture








Definition of brazing and soldering
Examples
Comparison with other welding processes
Heat sources
Brazing filler metals and solders
Fluxes and atmosphere
Set up and joint shape
Phenomena in brazing and soldering
–
–
–
–
–
–
–
–
Please remember
in your experimental
training (Sept.19 ?)

Wetting ( surface and interfacial tension )
Conduction of heat
Dissolution
Flow
Diffusion
Deformation
Oxidation - reduction reaction
Solidification -> microscopic structure
Exercise
Definition of the brazing and soldering.





Joint is heated
distributing filler metal between base materials,
by capillary action
below solidus temperature of base materials.
Sometimes the joint is pressed.
example of brazing
main engine LE7A
H2A rocket
Filler metals

Brazing
melting point of filler metal > 723 K （ 450 C, 840 F ）

Soldering
melting point of filler metal < 723 K （ 450 C, 840 F ）
Capillary action
Wetting phenomenon


Surface tension
or
Surface energy
A g - C u p h ase d i ag r am .
Solidus temperature

phase diagram
– Equilibrium
phase
– Lever rule
Solidus
Liquidus
example
Soldering is key technology
in micro-electronics assembly
example
Soldering is key technology
in micro-electronics assembly
example
“flip chip” technology
Solders for electronics
A ssessed P b - Sn p h ase d i ag r am .

conventional solder
– Sn-Pb
(Sn-38Pb 180C)

lead free solders
– Sn-Ag
–
–
–
–
(Sn-3.8Ag 220C)
Sn-In
Sn-Bi
Sn-Zn
etc...
Eutectic phase
Wire bonding by Kaijo
by H.Miyazaki, S.Saito, et.al...
Pb ( lead ) problem for health

Mental development index – age

Audition handicap - Pb in blood
Blood pressure - Pb in blood
(positive correlation)

->
Solders for electronics
A ssessed P b - Sn p h ase d i ag r am .

conventional solder
– Sn-Pb
(Sn-38Pb 180C)

lead free solders
– Sn-Ag
–
–
–
–
(Sn-3.8Ag 220C)
Sn-In
Sn-Bi
Sn-Zn
etc...
eutectic phase


Solders for electronics

A ssessed A g - Sn p h ase d i ag r am .

conventional solder
– Sn-Pb
(Sn-38Pb 180C)

lead free solders
– Sn-Ag
–
–
–
–
(Sn-3.8Ag 220C)
Sn-In
Sn-Bi
Sn-Zn
etc...

Sn-Ag-Bi-Sb-Cu
Sn-Ag-In
Sn-Ag-Bi-Cu
...
Problems Pb free solder

Melting point
problems in processes

Viscosity

Corrosion
– Heating iron
– Solder bath
 almost solved
 still under R/D
in iron soldering
in reflow soldering
example
Al brazing
example
Ni brazing
example
Ag brazing of Stainless and Ceramics

The highest technology is
never used for space
development.

The highest technology is the
combination of conventional
technologies.

Optimization & breakthrough
are based on scientific
understanding
Comparison with other welding or joining processes

melting base materials
ex. arc welding, resistance welding, etc…

adding molten metals between base materials
ex. brazing, soldering, etc...

not melting base materials
ex. solid phase bonding, hot pressing, etc...
Diffusion bonding, Hot pressing,
and Solid phase bonding
Samples are
– heated,
and
– pressed.
– Sometimes metal
sheet is inserted.
“filler metal” ?
in brazing
Another type of equipments

Hot Isostatic Pressing (HIP)
Example
Ni alloy

Requirements for joining
– to bring atoms near stable inter-atomic distance
?
Energy(arb.unit)
Activation Energy
Surface Energy
(a) Bulk or interface
(b) Activated surface
(c) Reduced surface
(equilibrium)
Phenomena


Soldering and Brazing


and also



Diffusion bonding
Hot pressing
Solid phase bonding






Wetting
Heat transfer
Dissolution
Flow
Diffusion
Deformation
Oxidation
Reduction
Solidification
Heat sources for brazing and soldering








Oxyfuelgas flame
Arc plasma
Joule’s heat
Induction heat
Hot iron
Ultrasonic wave
Infrared ray
Laser beam
etc...
:Torch brazing/soldering , braze welding
:Arc brazing, braze welding
:Resistance brazing
:Induction brazing
:Iron soldering
:Ultrasonic soldering
:Infrared soldering
:Laser beam soldering
Other terminology
for brazing and soldering
Atmosphere
 Atmospheric brazing/soldering

Vacuum brazing

Furnace brazing

Dip brazing/soldering
– Metal bath brazing/soldering
– Salt bath brazing/soldering
ex. of dip soldering
(in molten solder bath)
(in flux)
Other terminology
Procedure
 Abrasion tinning & re-flow
 Re-flow soldering
 Diffusion brazing/soldering
– Transient Liquid Phase bonding
ambiguous
ex. Re-flow used in electronics
Diffusion bonding ( Hot pressing ) ?
– Liquid phase diffusion bonding
– Eutectic bonding
: iso-thermal solidification
: no filler metal and
intent to melt base materials
Brazing/Soldering temperature
A ssessed P b - Sn p h ase d i ag r am .
= Liquidus temp. + 50~100 K
( because of viscosity )
Brazing filler metals and solders

Brazing filler metals in Japanese Industrial Standards (JIS)
Al,
Al alloy
Mg,
Mg alloy
Cu,
Cu alloy
Carbon
steel
Cast iron
Stainless
steel
Ni,
Ni alloy
Ti,
Ti alloy
Be, Zr, V,
alloy
W,Mo,Ta,
Nb, alloy
Al,
Al alloy
BA
Mg,
Mg alloy
----
BMg
Cu,
Cu alloy
----
----
BAg, BAu
BCuP,
BCuZn
Carbon
steel
BA
----
BAg, BAu
BCuZn
BAg, BAu
BCu, BNi,
BCuZn
Cast iron
----
----
BAg, BAu
BCuZn
BAg, BAu
BCuZn
BAg, BNi
BCuZn
Stainless
steel
BA
----
BAg, BAu
BAg, BAu
BCu, BNi,
BAg, BAu
BCu, BNi,
BAg, BAu
BCu, BNi,
Ni,
Ni alloy
----
----
BAg, BAu
BCuZn
BAg, BAu
BCu, BNi,
BCuZn
BAg, BCu
BCuZn
BAg, BAu
BCu, BNi
BAg, BAu
BCu, BNi
Ti,
Ti alloy
BA
----
BAg
BAg
BAg
BAg
BAg
**
Be, Zr, V,
alloy
---BA(Be)
----
BAg
BAg, BNi*
BAg, BNi*
BAg, BNi*
BAg, BNi*
**
**
W,Mo,Ta,
Nb, alloy
----
----
BAg
BAg, BCu, BAg, BCu
BNi*
BNi*
BAg, BCu
BNi*
BAg, BCu
BNi*
**
**
**
High speed
---steel
----
BAg, BAu
BCuZn,
BNi
BAg, BAu
BCu, BNi,
BCuZn
BAg, BAu
BCu, BNi
BAg, BAu
BCu, BNi,
BCuZn
----
----
----
---- : No filler metal,
* : modified (not standard)
BAg, BAu
BCuZn,
BNi
** : not standard
High speed
steel
BAg, BAu
BCu, BNi,
BCuZn
s
1
d
2
1
H
Li Be
Na Mg
K Ca Sc
Rb Sr Y
Cs Ba La
Fr Ra Ac
2
Ti
Zr
Hf
3
4
5
p
6
V Cr Mn Fe
Nb Mo Tc Ru
Ta W Re Os
7
8
Co
Rh
Ir
9
10
1
B
Al
Ga
In
Tl
2
C
Si
Ge
Sn
Pb
3
4
N
P
As
Sb
Bi
O
S
Se
Te
Po
14
Lu
Lr
Ni
Pd
Pt
Cu
Ag
Au
Zn
Cd
Hg
3
4
5
6
7
8
Nd Pm Sm Eu Gd Tb
U Np Pu Am Cm Bk
9
Dy
Cf
10 11 12 13
Ho Er Tm Yb
Es Fm Md No
f
1
Ce
Th
2
Pr
Pa
5
6
F
Cl
Br
I
At
He
Ne
Ar
Kr
Xe
Rn
Fluxes and atmosphere
Fluxes


Shielding
Reduction of surfaces
Requirements
 wettable
 easily removable
 never harmful
Shielding gas
Wettability
Set up and joint shape
Phenomena in brazing and soldering








Wetting ( Surface and interfacial tension )
Conduction of heat
Dissolution
Flow
Diffusion
Deformation
Oxidation - reduction reaction
Solidification -> microscopic structure
Wetting driven by
surface and interfacial tension

What determines equilibrium
( contact angle, meniscus, etc… ) ?
– surface and interfacial tension

Young’s equation
 s   i   l cos
Surface and interfacial tension
(Surface tension is interfacial tension between material and vacuum.)

Surface ( interfacial ) tension
– ex. soap film
– ex. soap bubble

Force on meniscus
Laplace equation

1
1 
P   l   
 R1 R2 
Effect of gravity on meniscus
on shape of fillet
– Curvature changes with height.
Surface (interfacial) tension
and Surface (interfacial) energy

Internal energy and entropy
Vb
U tot  U b  U s S tot  S b  Ss

p, T
A
1st law and 2nd law of thermodynamics
dU tot  TdStot  pdVb  dA


dU b  TdSb  pdVb
For bulk,
dUs  TdSs  dA
therefore
Variables for unit area of surface
Us  Us A

 ( p, T )  U s ( p, T )  TSs ( p, T )

 Us  T
Ss  Ss A
For arbitrary area of surface,
U   TS   dA  AdU  TdS  0
s
Therefore,
s
s
s
  Us  TSs dUs  TdSs
  
Ss   
 T  p
T
0
1  U s
T  T

 dT

p
Relation between
Surface (interfacial) tension and Surface (interfacial) energy
Surface ( interfacial )
tension
Surface ( interfacial )
energy
Surface ( interfacial )
entropy
 ( p, T )  U s ( p, T )  TSs ( p, T )

 Us  T


T
0
1  U s
T  T

 dT

p
Surface contribution of internal energy is important.
at 0 K,   U s
  
Ss   
 T  p
T

0
1  U s

T  T

dT

s (mJ/m2)
Theoretical approach for
surface tension at 0 K
3000
2500
2000
Be

Shifted step potential
Al
Zn
Ga
500
Stabilized
jellium
Mg
Cd
In
Pb
Hg
Li
Ca
Sr

Na

SCF-Jellium
K
Rb
Stabilized jellium
J.P.Predew, H.Q.Tran and E.D.Smith,
Phys. Rev. B, 42, 11627 (1990).
Ba
100
Shifted step potential
K.Takahashi, and T.Onzawa,
Physical Review B, 48, 5689 (1993)
1500
1000
Surface energy at zero tempetrature
Electronic theory
(quantum mechanics)
Cs
2
3
4
5
6
Effective electron density parameter rm (Bohr)
SCF-jellium
N.D.Lang and W.Kohn,
Phys. Rev. B, 1, 4555 (1970).
comparison by K.F.Wojciechovski, Surface Science, 437, 285-288 (1999)
Other contributions
( phonon, phase transformation )
T
 ( p, T )  U s  T 

0


1  U s
T  T


 dT

p

U s  U s, electron  U s, phonon  U s, phase trans.
=0, at 0 (zero) K.
 2 kF4
U s,electron (T ) 
K r (r , )
5m
Surface energy Us

Phonon
+
Electron
Phase transf.
Electron
0
Surface tension 
Temperature dependence
of surface tension
0,ext.
Tm
T
0

Solid
0
liquid
Tm
T
Experimental
measurements of
surface tension
Experimental value
which theorists
have been used,
is…
“extrapolated”
1.1
1.0
Al
0
0,ext.
Tm
T
0
Zn
0.7
0.6
s (mJ/m2)
Electron
0.8
Sn
0.5
0.4
Bi
Li
0.3
Na
0.2
Hg
K
0.1
Solid
0
Tm
Rb
Cs
liquid
T
0.0
0
500
1000
Temperature T (K)
3000
2500
2000
1500
Be
Shifted step potential
1500
Al
1000
Pb
Surface energy at zero tempetrature
Phase transf.
Surface tension s (J/m2)
Phonon
+
Electron
Surface tension 
Surface energy Us
0.9
Zn
Ga
500
Stabilized
jellium
Mg
Cd
In
Pb
Hg
Li
Ca
Sr
Ba
Na
SCF-Jellium
100
K
Rb
Cs
2
3
4
5
6
Effective electron density parameter rm (Bohr)
Strategy by lecturer for...
Data base of
Surface- and interfacial- tension
Experimental approaches
•
•
•
•
Cleavage method
Zero creep method
Thermal grooving method
Contact angle method
( sessile drop )
• Adhesion force method
• ...
Theoretical approaches
•
•
•
•
Quantum mechanics
Thermodynamics
Molecular dynamics
…
!! No experimental method gives perfect information by itself.
!! No theory gives perfect information by itself.
Conduction of heat (1)

Fourier's Law
q   grad T
Heat flux (J/m2s)
Thermal conductivity (J/sKm, W/Km)
Temperature (K)

Diffusion equation
T
1

  div q 
div grad T   D div grad T 
t
c
c
Latent heat (J/kgK)
Density (kg/m3)
Diffusion coefficient (m2/s)

D

c
Diffusion equation for Cartesian coordinate system
  2T  2T  2T 
T
 D 2  2  2 
t
y
z 
 x
Conduction of heat (2)

Solutions for special boundary conditions
– Steady state (t=), one dimensional
  2T 
T
 D 2   0
t
 x 
T ( x)  C1 x  C2
– Steady state (t=), axially symmetric
  2T 1 T 
T
  0
 D 2 
t
r r 
 r
T (r )  C1 ln r  C2
– Steady state (t=), center symmetric
  2T 2 T 
T
  0
 D 2 
t

r
r

r


1
T ( r )  C1  C 2
r
Y-AXIS
0.4
Conduction of heat (2)
0.2
0

Basic solutions of diffusion equation
– one dimensional
Q
T
c


-10
for heat input Q
Q (J/m)
linear heating
 x   2   y   2 
Q 1

T
exp 

c 4Dt
4 Dt


– three dimensional

0
X-AXIS
area heating
 x   2 
1

exp 
4 Dt 
4Dt

– two dimensional
-20
Q (J/m2)
point heating
 x   2   y   2  z   2 
Q
1

T
exp 
3/ 2

c 4Dt 
4 Dt


Q (J/m3)
10
20
l
Dissolution
s
increasing
 temperature
A g - C u p h ase d i ag r am .
L
i
– heating
– heat conduction

concentration
– filler metal
– diffusion
Solubility limit
Phase diagram
S
Flow

Wettability

driving force

Viscosity

dragging force

Approximation “Liquid is always uniform.”
Diffusion

Fick’s 1st law, Fick’s 2nd law, and Diffusion equation
  2C  2C  2C 
C
 D 2  2  2 
t
y
z 
 x
Application of basic solutions
 x   2 
c0

C
exp 
4 Dt 
4Dt

Y-AXIS

1
0.5
0
-10
0
10
X-AXIS
C
c0 
x 


1  erf  
2
4
Dt


where
erf   
2



0


exp   2 d
Diffusion

When material P is joined with
insert (filler) metal, change in
concentration profiles across
bond interface.

x

C  cs 1  erf  
4 Dt





and if





below eutectic temperature…
joint of P and Q at T0 ,…
joint of P and Q at <Teutectic ,…
Q is inserted,...
etc...
Deformation




: Deformation around joint
Elastic deformation
usually negligible
Plastic deformation
Creep deformation
Diffusional deformation
( diffusional creep )
L
Before contact
h00
Surface
After plastic deformation
Void
During creep deformation
– surface diffusion
– boundary diffusion
– volume diffusion
X
(a)
Boundary diffusion
Void
Solid phase bonding
Surface diffusion
Volume diffusion
(b)
Time required for perfect contact by deformation
L
Void
10
10
10
10
10
(s)
5
10
10
L=10  m , h 00 =1  m
4
3
L=1  m , h 00 =0.1  m
2
1
0
800
1000
Tem perature T
1200
(K)
6
T=1000 K
t fin
P b =10 M Pa
10
Tim e required for perfect contact
6
Tim e required for perfect contact
10
t fin
(s)
X
10
10
10
10
10
5
L=10  m , h 00 =1  m
4
3
2
L=1  m , h 00 =0.1  m
1
0
0
5
10
Bonding pressure
Pb
15
(M Pa)
20
L=10m, h 00=1 m, P b=10MPa
Volume diffusion


Boundary diffusion
50
Creep deformation
0
Plastic deformation
800
– surface diffusion
– boundary diffusion
– volume diffusion
1000
Bonding temperature
T (K)
1200
L=10m, h 00=1 m, T=1000K
100
Volume diffusion
S (%)

Elastic deformation
Plastic deformation
Creep deformation
Diffusional deformation
Why it is called
“diffusion” bonding ?
L
Void
X
Percent bonded area

Percent bonded area
Dominant mechanism
S (%)
100
Boundary diff.
50
Creep deformation
0
0
Plastic deformation
10
Bonding pressure
Pb
(MPa)
20
L=10m, h 00=1 m, P b=10MPa
50
Creep deformation
popular
roughness
Plastic deformation
800
Volume diffusion
100
Percent bonded area
S (%)
Percent bonded area
Boundary diffusion
0
L=1m, h 00=0.1 m, P b=10MPa
S (%)
Volume diffusion
100
If you want to use
diffusion for precise
joining…
1000
Bonding temperature
T (K)
Boundary diffusion
50
Creep deformation
0
1200
Plastic deformation
800
L=10m, h 00=1 m, T=1000K
Percent bonded area
50
Creep deformation
L
Void
0
Plastic deformation
10
Bonding pressure Pb
(MPa)
20
X
1200
Volume diffusion
S (%)
100
Percent bonded area
If carefully
prepared...
Volume diffusion
Boundary diff.
0
T (K)
L=1 m, h 00=0.1 m, T=1000K
S (%)
100
1000
Bonding temperature
Boundary diffusion
50
Creep deformation
0
0
Plastic deformation
10
Bonding pressure Pb
(MPa)
20
Oxidation - reduction reaction between fluxes and metal

ex. Cu joint by Pb-Sn solder with HCl flux
– Reduction of base metal surface
CuO  2HCl  CuCl 2  H2O 
– Shield of molten metal
Sn  2HCl  SnCl 2  H2 
– Assist wettability
Cu  SnCl 2  CuCl 2  Sn
Oxidation - reduction reaction between atmosphere and metal
ex. atmospheric brazing with hydrogen gas

MmOn  nH2   m M  nH2O  G0
G
0
H 2O
 G
0
H2
 pH 2 O 

 G   RT ln K   RTn ln
 pH 
 2 
0
depending on
 Material (M)
 Partial pressure of H2O
 Partial pressure of H2


Liquid N2 trap, Silica gel, etc...
Gas control
Solidification

Phase diagram

precipitation process

Microscopic structure

Mechanical property
– materials
– cooling rates
ex. Fe-C system
P b - Sn p h ase d i ag r am .
ex. Pb-SnA ssessed
solder
eutectic phase
Ball Grid Array (BGA)
in “flip chip” technology
Eutectic phase can be seen.
Weakness of low melting point material
ex. Pb-Sn solder

Cracking

Thermal effect
150 C 100 hours
Brittleness
of inter-metallic
A ssessed
F e- A l p h ase d i ag r am . compound
ex. Fe - Al
Although Al is low melting point material,...
ex. filler metal for Al: Low melting point  precise heat control
A ssessed A l - Si p h ase d i ag r am .
A ssessed A l - M g p h ase d i ag r am .
A ssessed A l - Z n p h ase d i ag r am .
A ssessed A l - C u p h ase d i ag r am .
Weld metal solidification crack
ex. Al

at the end of the solidification,

the liquid vanish very quickly
lack of liquid
crack
ex. Ti - Ti bonding with Cu film
A ssessed T i - C u p h ase d i ag r am .
Exercise 1
Schematically, illustrate a concentration profile at 700 C across the
A g - C u p h ase d i ag r am .
interface of diffusion couple (Ag/Cu), considering phase diagram.
Exercise 2
Cu samples are bonded using insert film of Ag by keeping joint at
900 C. After liquid metal vanished, the joint was cooled to room
temperature. Schematically, illustrate a change of concentration
profile across the interface.
A g - C u p h ase d i ag r am .
Exercise 3
Choose a percentage of Sn in Pb-Sn solder.
A ssessed P b - Sn p h ase d i ag r am .
And answer a soldering temperature.
Exercise 4
List up deformation mechanisms for solid phase bonding.
fin.
ボツ
Conduction of heat

Application of basic solutions
– Step distribution in t=0.
– Area heating
– Linear heating
– Point heating

Thermal conductivity, Specific heat, Mass density
Temperature dependence
Thermal diffusion coefficient
Surface and interfacial tension
(Surface tension is interfacial tension between material and vacuum.)

Meniscus between flat plane