Advances in solder ball placement for surface-mountable packages
The continuing trend for the
miniaturisation of portable electronic
Advances in
devices, combined with the demand
for ever-greater functionality from
those devices, has driven many
solder ball
surface mount designers away from
the traditional SMT leaded package
selections of PLCC, QFP, TSOP
placement for
etc, and towards packages with an
area grid array footprint. Whilst the
benefits of this move are numerous,
the two biggest advantages are a) a
surface-mountable
smaller overall component outline
and b) a faster signal path from chip
to SMT circuit board.
packages
This trend towards area
array technology is already well
Tom Falcon, DEK Printing Machines Ltd, Weymouth, Dorset, U.K
established, and the resultant
explosion in demand for these
packages has led to some unique
challenges for solder ball placement
Fig. 10b Vacuum transfer ball placement. Placement.
equipment manufacturers, one
of the most obvious of which is
Fig. 1. Underfill
Overmold
Flip Chip Die
Low Positive Pressure
the inexorable decrease in solder
ball diameters, particularly for
the kind of miniature packages
used in mobile phones, PDAs,
etc. Other challenges include ball
placement onto silicon wafers for
the increasingly popular wafer-level
chip scale package (or WLCSP),
and there’s also an increase in
Interposer
Solder Balls
demand for ball placement onto
Wafer Wafer
BGA modules (system in package,
or SiP), each of which can house
Fig. 5 Cross section of WBGA
Tooling
Figure 1. Cross-section of a flip chip BGA.
multiple silicon and discrete
components in a single package.
Wire Bonds
Overmold
This paper will attempt to
Ball array packages for SMT flip chip or wire-bonded die on one side
From its humble beginnings in the first and 0.4 to 0.762 mm diameter balls on Fig 11a. Wafer tooling:
explore these challenges and describe
BGAs during the 1990s, ball grid array the other side, BGAs can be produced in
methods of ball placement capable of technology has exploded into a huge panels or strips, or as singulated parts in
addressing them.
variety of package types. Even when we JEDEC carriers.
ignore the multitude of different internal By its very definition, solder balling
constructions for these package types, there is absolutely fundamental
0.
to the efficacy Pallet
Vacuum Wafer
is still a vast range of different form factors, of the BGA. Figure 1 illustrates 2 a cross-
Channels
Keywords: Ball Placement, Ball
materials and ball diameters that must section of a typical flip chip BGA.
Attach, DEK, BGA,
6
be accommodated by the ball placement System in package or modules
CSP, WLCSP.
equipment supplier. ITRS (International Technology Roadmap
Fig 11b. Flux Print:
Substrate
for Semiconductors) classify the system
BGAs Silicon Die in
Solder Balls
package (SiP) as “a combination of
Flux
Screen
Typically an overmolded or lidded multiple active electronic components
Squeegee
interposer, 10 to 50 mm square, with a of different functionality, assembled in
Fig. 10a Vacuum transfer ball placement. Pick-up.
12 – Global SMT & Packaging - August 2008
www.globalsmt.net
Pallet
Vacuum Wafer
Channels
Vacuum
Machined
Tool
Reservoir
Fig. 11c. Ball Placement:
Direction
Ball Place
of Travel
Transfer Head
Pallet
Ball Place
Wafer
Stencil
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