<s>
In	O
integrated	B-Algorithm
circuit	I-Algorithm
packaging	I-Algorithm
,	O
a	O
solder	B-Algorithm
ball	I-Algorithm
,	O
also	O
a	O
solder	O
bump	O
(	O
often	O
referred	O
to	O
simply	O
as	O
"	O
ball	O
"	O
or	O
"	O
bumps	O
"	O
)	O
is	O
a	O
ball	B-Algorithm
of	I-Algorithm
solder	I-Algorithm
that	O
provides	O
the	O
contact	O
between	O
the	O
chip	B-Algorithm
package	I-Algorithm
and	O
the	O
printed	O
circuit	O
board	O
,	O
as	O
well	O
as	O
between	O
stacked	O
packages	O
in	O
multichip	B-Algorithm
modules	I-Algorithm
;	O
in	O
the	O
latter	O
case	O
,	O
they	O
may	O
be	O
referred	O
to	O
as	O
microbumps	B-Algorithm
( μbumps	O
,	O
ubumps	O
)	O
,	O
since	O
they	O
are	O
usually	O
significantly	O
smaller	O
than	O
the	O
former	O
.	O
</s>
<s>
The	O
solder	B-Algorithm
balls	I-Algorithm
can	O
be	O
placed	O
manually	O
or	O
by	O
automated	O
equipment	O
,	O
and	O
are	O
held	O
in	O
place	O
with	O
a	O
tacky	O
flux	O
.	O
</s>
<s>
A	O
coined	B-Algorithm
solder	I-Algorithm
ball	I-Algorithm
is	O
a	O
solder	B-Algorithm
ball	I-Algorithm
subject	O
to	O
coining	O
,	O
i.e.	O
,	O
flattening	O
to	O
a	O
shape	O
resembling	O
that	O
of	O
a	O
coin	O
,	O
to	O
increase	O
contact	O
reliability	O
.	O
</s>
<s>
The	O
ball	B-Algorithm
grid	I-Algorithm
array	I-Algorithm
,	O
chip-scale	B-Algorithm
package	I-Algorithm
,	O
and	O
flip	B-Device
chip	I-Device
packages	O
generally	O
use	O
solder	B-Algorithm
balls	I-Algorithm
.	O
</s>
<s>
After	O
the	O
solder	B-Algorithm
balls	I-Algorithm
are	O
used	O
to	O
attach	O
an	O
integrated	O
circuit	O
chip	O
to	O
a	O
PCB	O
,	O
often	O
the	O
remaining	O
air	O
gap	O
between	O
them	O
is	O
underfilled	O
with	O
epoxy	O
.	O
</s>
<s>
In	O
some	O
cases	O
,	O
there	O
may	O
be	O
multiple	O
layers	O
of	O
solder	B-Algorithm
balls	I-Algorithm
—	O
for	O
example	O
,	O
one	O
layer	O
of	O
solder	B-Algorithm
balls	I-Algorithm
attaching	O
a	O
flip	B-Device
chip	I-Device
to	O
an	O
interposer	O
to	O
form	O
a	O
BGA	O
package	O
,	O
and	O
a	O
second	O
layer	O
of	O
solder	B-Algorithm
balls	I-Algorithm
attaching	O
that	O
interposer	O
to	O
the	O
PCB	O
.	O
</s>
