Page 25 - Chip Scale Review_Jul Aug_2022-digital

A 55GHz octal-site probe card for 5G mmWave devices

By Peter Cockburn [Cohu, Inc.]

T o support higher bandwidth

5G connections, suppliers of
high-end smartphones are
starting to integrate compact antenna
modules that support multi-channel,
beam-forming mmWave interfaces at
frequencies of 24GHz – 48GHz. These
rely on complex silicon implemented
in fine-pitch, wafer-level packages that
need to be comprehensively tested before
integration as part of a known good
die (KGD) strategy. This in turn puts
new challenges on the suppliers of test
equipment and test interfaces, namely:

• Automatic test equipment (ATE)
systems need to offer cost-effective,
mmWave test options with high
parallelism; and
• Test interfaces – contactors for
package test and probe cards for
test of bare die or wafer-level
packages (WLPs) – must support
the fine pitches and high signal Figure 1: Probe card front.
frequencies used.

At SWTest 2021, J. Mroczkowski
described a probe card for testing
w a fe r-le vel ch i p - sca le pa ck age
( W LCSP) m mWave dev ice s t h at
suppor ted high-bandwidth radio-
frequency (RF) connectivity for both
direct and loopback testing [1]. This
is implemented using a direct-attach
printed circuit board (PCB) technology
that supports a 150μm-pitch fan out.
This method allows a large amount
of test functionality to be included
in an 8-site layout and minimizes the
transitions for mmWave signals that
are routed directly from the device
under test (DUT) area across the PCB
surface via coplanar waveguide (CPW)
structures to RF cable connectors.
Each site requires the use of over
600 cViper spring probes at 150μm
pitch and the probe head design allows
for the attachment of a manual test
option that can be used across all eight
sites simultaneously to test singulated
bumped die (see Figures 1 and 2).
Figure 2: Probe card back.

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