May 2013 - I-Micronews

M A Y 2 0 1 3 I S S U E N ° 2 7
A CLOSER LOOK
The evolution of flip chip
packaging
Flip chip (FC) has had a pronounced impact on advanced packaging but do we
all know when and where these historic technology developments occurred? 3D
Packaging decided to take …a closer look.
IBM introduces flip chip
IBM introduced the FC concept in 1964 on the
IBM System 360 mainframe computer with solder
coated copper balls. In 1969 they introduced
solid solder balls - i.e. the controlled collapse chip
connection (C-4).
Intel eliminates resistance to new FC
processing technologies
The initial resistance to accept these non IBM
technologies was alleviated in 1999 when
Intel announced the use of Ti/Ni UBM for their
microprocessor packaging technology.
Redistribution - Area array FC from
chips designed with peripheral pads
One impediment to the use of FC was the lack of
FC designed chips. This was addressed in 1994
by Chanchani and co-workers who developed
redistribution layer technology (RDL).
IBM logic chip circa 1970 (Courtesy of IBM)
For the next two decades FC was mainly confined
to ceramic packaging in high end main frame
computers due to the CTE mismatch between Si
vs PCB laminates.
Underfilling – the key to reliability
Redistribution requires secondary passivation (thin
film polymers such as BCB and PI) and metallization
(typically Cu or Al) to reroute the peripheral pads
to a looser pitch area array configuration.
Aluminum or Copper
Redistribution
Line
Second passivation
Solder
Primary passivation
Terminal
In 1987 Hitachi revealed that FC die mounted in
ceramic packages had better reliability when the
area surrounding the solder balls was encapsulated
with an epoxy “underfill”. In 1992, Tsukada of
IBM Japan reported that FC could be reliably
used on PWB laminate if the chips were similarly
underfilled.
Silicon
Bond Pad
Active Circuits
“We have come
a long way since
IBM introduced
the flip chip
concept in 1964,”
says Dr Philip Garrou.
Driving down the processing cost –
FCT and Unitive
During the 1990’s lower cost bumping processes
were developed by the Microelectronics Center of
NC [MCNC] and its spin out company Unitive Inc
and the joint venture of Delco and KNS, Flip Chip
Technologies (FCT). Their developments of lower
cost UBMs (FCT - Al/Ni-V/Cu; Unitive - Ti/Cu/Ni)
and lower cost solder deposition technologies (FCT
- stencil printing; Unitive - plating) and their use of
redistribution (see later discussion) in combination
with the Tsukada revelation that bumping could
be used reliably on laminate, opened the door for
widespread acceptance of FC.
Redistribution (cross section (Top) and top
down (Bottom)) (Courtesy Unitive Electronics)
Wafer Level Packaging (WLP)
The next major breakthrough came with the
concept of wafer level packaging. WLP describes
a package which is fully fabricated on the wafer
before dice and subsequent surface mount.
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3 D P a c k a g i n g