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a nd i m p e d a n c e m a t c h i n g w i t h
si mu l a t io n s , a t e s t f i x t u r e wa s
required. A customized test fixture
(test PH w it h 27 need les — 8 R F
loopback and 19 GND needles) was
designed to “sandwich” the probe
h e a d b e t we e n 5 0 Ω i m p e d a n c e -
cont rolled t races at each end to
allow VNA interface. A total of 16
2.92mm connectors (8 head side + 8
tip side) enabled four simultaneous
port measurements.
The following is a discussion of
the test fixture measurement results.
We found that IL and RL have a high
degree of variability due to radio
frequency (RF) space transformer
microstrip manufacturing tolerance,
i mped a nce m ismat che s bet wee n
Figure 11: Contact test results of Merlion 6. the SMA connector to the trace and
mechanical assembly (see Figure
12). F i g u r e 13 sho w s t h a t t h e
single-ended cross-talk simulation
of the probe needle matches the
measurement. Because it’s possible
t o e va l u a t e t h e p l o t i n F i g u r e
14, the TDR measurement shows
good agreement in predicting the
probe head impedance profile. De-
embedd i ng is per for med on test
p oi nt s w it h t he b e st i mp e d a nce
profile. De-embedded S-parameters
measurement shows good IL and RL
correlation with simulation.
Probe head characteri zat ion:
probe card external loopback end-
t o - e n d me a s u r e me nt . I n o r d e r
Figure 12: Test fixture SE S parameters simulation vs. measurement. to improve characterization data,
f u r ther measu rements have been
done, e.g., four (RF) microprobes
were used to directly contact the
signal probes and the nearest ground
p ro b e. T h e t e s t set up i n cl ud e d
microprobes that were positioned and
put in contact using a probing station
with four manual micro-positioners,
RF microprobes have been connected
to a vector network analyzer (VNA)
for S-parameter acquisition. The TDR
plot was generated by simulation.
R F m i c r o p r o b e m e a s u r e m e n t
r e s u lt s c om p a r e d t o si mu l at io n
results are shown in Figure 15. To
better match the measurements with
the simulation results, it is necessary
to take into account the buckling
Figure 13: Test fixture SE cross talk TDR parameters (simulation vs. measurement).
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