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Advances in solder ball placement for surface-mountable packages
Ball array package market
As can be seen in Figure 7, the growth of
area array packages as a percentage of all
ICs is pretty impressive.
However, when we consider that
the total IC market is also growing at
an approximate annual rate of 8% then
area array package sales growth is quite
phenomenal.
Figure 8 illustrates this with
Prismark’s forecast for the next few
years. The red arrows highlight some
impressive numbers, including an 89%
compound annual average growth rate
for the flip chip CSP. Much of this
growth is driven by the mobile phone
market, which now stands at over one
billion handsets per year. With multiple
area array packages in each handset
even at the low end of the functionality Figure 6. ST Micro 0.4mm pitch WLCSP (Bluetooth & FM radio STLC2690).
spectrum, the shear numbers involved
are staggering. Clearly the need for high
volume ball placement process solutions
is growing just as rapidly as these
components.
In addition to the above, there are
further indicators that some area array
component types are set to take off.
For example, some industry analysts say
that due to falling memory prices, solid
state hard drives (which currently cost
many times more than the spinning disk
alternatives) will become cost effective
by 2009/2010. This will ensure that a
significant proportion of the notebook
market adopts SSDs and that the NAND
memory market will grow accordingly.
Ball placement methods
Over the last 10 years or so, the
packaging industry has developed several
Figure 7. Planar packaging interconnect trends (source: Prismark).
methods for the mass transfer of solder
balls to wafers (and a few more for
rework, or single ball placement). The
most popular by far for high-volume
ball placement are the vacuum transfer
method and the stencil printing method.
The vacuum transfer method, illustrated
in Figure 10, is fairly simple in theory,
the principle of operation being to
firstly machine a vacuum tool with an
appropriately sized through-hole for
each ball location on the component.
This tool can then be used to ‘vacuum
pick’ solder balls from a reservoir and
later place them onto the pre-fluxed
component, either by releasing the
vacuum or by reversing the air flow
to provide a small amount of positive
pressure. This method can be used to
place whole wafers/panels/strips, or to
‘step and repeat’ placement of smaller
areas or individual components.
Figure 8. Overview of IC package unit growth (source: Prismark).
14 – Global SMT & Packaging - August 2008 www.globalsmt.net
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