<s>
Glass	B-Algorithm
frit	I-Algorithm
bonding	I-Algorithm
,	O
also	O
referred	O
to	O
as	O
glass	O
soldering	O
or	O
seal	O
glass	O
bonding	O
,	O
describes	O
a	O
wafer	B-Algorithm
bonding	I-Algorithm
technique	O
with	O
an	O
intermediate	O
glass	O
layer	O
.	O
</s>
<s>
It	O
is	O
a	O
widely	O
used	O
encapsulation	B-Algorithm
technology	O
for	O
surface	O
micro-machined	B-Architecture
structures	I-Architecture
,	O
e.g.	O
,	O
accelerometers	O
or	O
gyroscopes	B-Application
.	O
</s>
<s>
This	O
technique	O
utilizes	O
low	O
melting-point	O
glass	O
(	O
"	O
glass	B-Algorithm
solder	I-Algorithm
"	O
)	O
and	O
therefore	O
provides	O
various	O
advantages	O
including	O
that	O
viscosity	B-Application
of	O
glass	O
decreases	O
with	O
an	O
increase	O
of	O
temperature	O
.	O
</s>
<s>
The	O
viscous	O
flow	O
of	O
glass	O
has	O
effects	O
to	O
compensate	O
and	O
planarize	O
surface	O
irregularities	O
,	O
convenient	O
for	O
bonding	O
wafers	O
with	O
a	O
high	O
roughness	O
due	O
to	O
plasma	B-Algorithm
etching	I-Algorithm
or	O
deposition	O
.	O
</s>
<s>
A	O
low	O
viscosity	B-Application
promotes	O
hermetically	O
sealed	O
encapsulation	B-Algorithm
of	O
structures	O
based	O
on	O
a	O
better	O
adaption	O
of	O
the	O
structured	O
shapes	O
.	O
</s>
<s>
This	O
results	O
in	O
low	O
stress	O
in	O
the	O
bonded	B-Algorithm
wafer	I-Algorithm
pair	O
.	O
</s>
<s>
Glass	B-Algorithm
frit	I-Algorithm
bonding	I-Algorithm
can	O
be	O
used	O
for	O
many	O
surface	O
materials	O
,	O
e.g.	O
,	O
silicon	O
with	O
hydrophobic	O
and	O
hydrophilic	O
surface	O
,	O
silicon	O
dioxide	O
,	O
silicon	O
nitride	O
,	O
aluminium	O
,	O
titanium	O
or	O
glass	O
,	O
as	O
long	O
as	O
the	O
CTE	O
are	O
in	O
the	O
same	O
range	O
.	O
</s>
<s>
Glass	O
frit	O
as	O
a	O
dielectric	O
material	O
does	O
not	O
need	O
additional	O
passivation	B-Application
for	O
preventing	O
leakage	O
currents	O
at	O
process	O
temperatures	O
up	O
to	O
.	O
</s>
<s>
Glass	B-Algorithm
frit	I-Algorithm
bonding	I-Algorithm
is	O
used	O
to	O
encapsulate	O
surface	O
micro-machined	B-Architecture
sensors	I-Architecture
,	O
i.e.	O
</s>
<s>
gyroscopes	B-Application
and	O
accelerometers	O
.	O
</s>
<s>
The	O
glass	O
frit	O
bond	O
procedure	O
is	O
used	O
for	O
the	O
encapsulation	B-Algorithm
and	O
mounting	O
of	O
components	O
.	O
</s>
<s>
photolithography	B-Algorithm
.	O
</s>
<s>
The	O
glass	B-Algorithm
frit	I-Algorithm
bonding	I-Algorithm
,	O
starting	O
with	O
alignment	O
of	O
the	O
wafers	O
,	O
is	O
a	O
thermo-compressive	O
process	O
that	O
takes	O
place	O
in	O
the	O
bonding	O
chamber	O
at	O
specific	O
pressure	O
.	O
</s>
<s>
Based	O
on	O
the	O
sufficiently	O
high	O
viscosity	B-Application
of	O
the	O
glass	O
,	O
bonding	O
can	O
take	O
place	O
nearly	O
without	O
pressure	O
.	O
</s>
<s>
The	O
bonding	O
temperature	O
needs	O
to	O
be	O
high	O
enough	O
to	O
reduce	O
the	O
viscosity	B-Application
of	O
the	O
glass	O
material	O
and	O
ensures	O
a	O
good	O
wetting	O
of	O
the	O
bond	O
surface	O
,	O
but	O
also	O
low	O
enough	O
to	O
prevent	O
overspreading	O
of	O
the	O
glass	O
frit	O
material	O
.	O
</s>
<s>
It	O
is	O
high	O
enough	O
,	O
around	O
20MPa	O
,	O
for	O
most	O
applications	O
and	O
comparable	O
to	O
those	O
achieved	O
with	O
anodic	B-Algorithm
bonding	I-Algorithm
.	O
</s>
<s>
The	O
hermeticity	O
ensures	O
the	O
correct	O
function	O
and	O
a	O
sufficient	O
reliability	B-Algorithm
of	O
the	O
bond	O
and	O
therefore	O
the	O
product	O
.	O
</s>
<s>
Two	O
types	O
of	O
glass	B-Algorithm
solders	I-Algorithm
are	O
used	O
:	O
vitreous	O
,	O
and	O
devitrifying	O
.	O
</s>
<s>
In	O
production	O
of	O
cathode	B-Device
ray	I-Device
tubes	I-Device
,	O
devitrifying	O
solders	O
based	O
on	O
PbO-B2O3-ZnO	O
are	O
used	O
.	O
</s>
<s>
Zinc-silicoborate	O
glasses	O
can	O
also	O
be	O
used	O
for	O
passivation	B-Application
of	O
electronics	O
;	O
their	O
coefficient	O
of	O
thermal	O
expansion	O
must	O
match	O
silicon	O
(	O
or	O
the	O
other	O
semiconductors	O
used	O
)	O
and	O
they	O
must	O
not	O
contain	O
alkaline	O
metals	O
as	O
those	O
would	O
migrate	O
to	O
the	O
semiconductor	O
and	O
cause	O
failures	O
.	O
</s>
<s>
The	O
bonding	O
between	O
the	O
glass	O
or	O
ceramics	O
and	O
the	O
glass	B-Algorithm
solder	I-Algorithm
can	O
be	O
either	O
covalent	O
,	O
or	O
,	O
more	O
often	O
,	O
van	O
der	O
Waals	O
.	O
</s>
<s>
The	O
seal	O
can	O
be	O
leak-tight	O
;	O
glass	O
soldering	O
is	O
frequently	O
used	O
in	O
vacuum	B-General_Concept
technology	O
.	O
</s>
<s>
Glass	B-Algorithm
solders	I-Algorithm
can	O
be	O
also	O
used	O
as	O
sealants	O
;	O
a	O
vitreous	O
enamel	O
coating	O
on	O
iron	O
lowered	O
its	O
permeability	O
to	O
hydrogen	O
10	O
times	O
.	O
</s>
<s>
Glass	B-Algorithm
solders	I-Algorithm
are	O
frequently	O
used	O
for	O
glass-to-metal	O
seals	O
and	O
glass-ceramic-to-metal	O
seals	O
.	O
</s>
<s>
Glass	B-Algorithm
solders	I-Algorithm
are	O
available	O
as	O
frit	O
powder	O
with	O
grain	O
size	O
below	O
60	O
micrometers	O
.	O
</s>
<s>
Due	O
to	O
their	O
low	O
viscosity	B-Application
in	O
molten	O
state	O
,	O
lead	O
glasses	O
with	O
high	O
PbO	O
content	O
(	O
often	O
70	O
–	O
85%	O
)	O
are	O
frequently	O
used	O
.	O
</s>
<s>
The	O
solvents	O
are	O
used	O
to	O
adjust	O
the	O
viscosity	B-Application
of	O
the	O
organic	O
binder	O
.	O
</s>
<s>
The	O
glass	O
used	O
for	O
MEMS	B-General_Concept
applications	O
consists	O
of	O
particles	O
and	O
lead	O
oxide	O
.	O
</s>
<s>
The	O
reduction	B-Operating_System
of	O
lead	O
oxide	O
by	O
the	O
silicon	O
leads	O
to	O
the	O
formation	O
of	O
lead	O
precipitations	O
at	O
the	O
silicon-glass	O
interface	O
.	O
</s>
<s>
Those	O
precipitations	O
decrease	O
the	O
strength	O
of	O
the	O
bond	O
and	O
are	O
reliability	B-Algorithm
risks	O
that	O
have	O
to	O
be	O
considered	O
for	O
the	O
lifetime	O
predictions	O
of	O
the	O
devices	O
.	O
</s>
<s>
Glass	B-Algorithm
solders	I-Algorithm
are	O
frequently	O
used	O
in	O
electronic	B-Algorithm
packaging	I-Algorithm
.	O
</s>
<s>
CERDIP	B-Algorithm
packagings	O
are	O
an	O
example	O
.	O
</s>
<s>
Outgassing	O
of	O
water	O
from	O
the	O
glass	B-Algorithm
solder	I-Algorithm
during	O
encapsulation	B-Algorithm
was	O
a	O
cause	O
of	O
high	O
failure	O
rates	O
of	O
early	O
CERDIP	B-Algorithm
integrated	O
circuits	O
.	O
</s>
<s>
As	O
the	O
seals	O
can	O
be	O
performed	O
at	O
much	O
lower	O
temperature	O
than	O
with	O
direct	O
joining	O
of	O
glass	O
parts	O
and	O
without	O
use	O
of	O
flame	O
(	O
using	O
a	O
temperature-controlled	O
kiln	O
or	O
oven	O
)	O
,	O
glass	B-Algorithm
solders	I-Algorithm
are	O
useful	O
in	O
applications	O
like	O
subminiature	O
vacuum	B-General_Concept
tubes	O
or	O
for	O
joining	O
mica	O
windows	O
to	O
vacuum	B-General_Concept
tubes	O
and	O
instruments	O
(	O
e.g.	O
,	O
Geiger	O
tube	O
)	O
.	O
</s>
<s>
The	O
expansion	O
matching	O
is	O
not	O
critical	O
in	O
applications	O
where	O
thin	O
layers	O
are	O
used	O
on	O
small	O
areas	O
,	O
e.g.	O
,	O
fireable	O
inks	B-Application
,	O
or	O
where	O
the	O
joint	O
will	O
be	O
subjected	O
to	O
a	O
permanent	O
compression	O
(	O
e.g.	O
,	O
by	O
an	O
external	O
steel	O
shell	O
)	O
offsetting	O
the	O
thermally	O
introduced	O
tensile	O
stresses	O
.	O
</s>
<s>
Glass	B-Algorithm
solder	I-Algorithm
can	O
be	O
used	O
as	O
an	O
intermediate	O
layer	O
when	O
joining	O
materials	O
(	O
glasses	O
,	O
ceramics	O
)	O
with	O
significantly	O
different	O
coefficient	O
of	O
thermal	O
expansion	O
;	O
such	O
materials	O
cannot	O
be	O
directly	O
joined	O
by	O
diffusion	O
welding	O
.	O
</s>
<s>
A	O
glass	B-Algorithm
solder	I-Algorithm
is	O
used	O
,	O
e.g.	O
,	O
for	O
joining	O
together	O
parts	O
of	O
cathode	B-Device
ray	I-Device
tubes	I-Device
and	O
plasma	O
display	O
panels	O
.	O
</s>
<s>
Electrically	O
conductive	O
glass	B-Algorithm
solders	I-Algorithm
can	O
be	O
also	O
prepared	O
.	O
</s>
<s>
The	O
following	O
advantages	O
result	O
from	O
using	O
the	O
glass	B-Algorithm
frit	I-Algorithm
bonding	I-Algorithm
procedure	O
:	O
</s>
