7
Assembly Techniques
The backside of the MMIC chip is RF ground. For mi-
crostrip applications the chip should be attached directly
to the ground plane (e.g. circuit carrier or heatsink) using
electrically conductive epoxy
[1,2]
.
For best performance, the topside of the MMIC should be
brought up to the same height as the circuit surrounding
it. This can be accomplished by mounting a gold plate
metal shim (same length and width as the MMIC) under
the chip which is of correct thickness to make the chip
and adjacent circuit the same height. The amount of
epoxy used for the chip and/or shim attachment should
be just enough to provide a thin llet around the bottom
perimeter of the chip or shim. The ground plan should
be free of any residue that may jeopardize electrical or
mechanical attachment.
The location of the RF bond pads is shown in Figure
24. Note that all the RF input and output ports are in a
Ground-Signal-Ground conguration.
RF connections should be kept as short as reasonable to
minimize performance degradation due to undesirable
series inductance. A single bond wire is normally suf-
cient for signal connections, however double bonding
with 0.7 mil gold wire or use of gold mesh is recom-
mended for best performance, especially near the high
end of the frequency band.
Thermosonic wedge bonding is the preferred method
for wire attachment to the bond pads. Gold mesh can
be attached using a 2 mil round tracking tool and a tool
force of approximately 22 grams and a ultrasonic power
of roughly 55 dB for a duration of 76 ± 8 mS. The guided
wedge at an ultrasonic power level of 64 dB can be used
for 0.7 mil wire. The recommended wire bond stage tem-
perature is 150 ± 2°C.
Caution should be taken to not exceed the Absolute
Maximum Rating for assembly temperature and time.
The chip is 100 µm thick and should be handled with care.
This MMIC has exposed air bridges on the top surface and
should be handled by the edges or with a custom collet
(do not pick up the die with a vacuum on die center).
This MMIC is also static sensitive and ESD precautions
should be taken.
Notes:
1. Ablebond 84-1 LM1 silver epoxy is recommended.
2. Eutectic attach is not recommended and may jeopardize reliability
of the device.
Figure 23. AMMC-6120 simplied schematic.
