6
Biasing and Operation
The AMMC-5618 is normally biased with a single positive
drain supply connected to both V
D1
and V
D2
bond pads
as shown in Figure 19(a). The recommended supply volt-
age is 3 to 5 V.
No ground wires are required because all ground con-
nections are made with plated through-holes to the
backside of the device.
Gate bias pads (V
G1
& V
G2
) are also provided to allow ad-
justments in gain, RF output power, and DC power dis-
sipation, if necessary. No connection to the gate pad
is needed for single drain-bias operation. However, for
custom applications, the DC current owing through
the input and/or output gain stage may be adjusted by
applying a voltage to the gate bias pad(s) as shown in
Figure 19(b). A negative gate-pad voltage will decrease
the drain current. The gate-pad voltage is approximately
zero volt during operation with no DC gate supply. Refer
to the Absolute Maximum Ratings table for allowed DC
and thermal conditions.
Assembly Techniques
The backside of the AMMC-5618 chip is RF ground. For
microstripline applications, the chip should be attached
directly to the ground plane (e.g., circuit carrier or heat-
sink) 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 plated
metal shim (same length and width as the MMIC) under
the chip, which is of the correct thickness to make the
chip and adjacent circuit coplanar.
The amount of epoxy used for chip and or shim at-
tachment should be just enough to provide a thin llet
around the bottom perimeter of the chip or shim. The
ground plane should be free of any residue that may
jeopardize electrical or mechanical attachment.
The location of the RF bond pads is shown in Figure
20. 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 sucient for sig-
nal connections, however double-bonding with 0.7 mil
gold wire or the use of gold mesh is recommended for
best performance, especially near the high end of the
frequency range.
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 with an ultrasonic pow-
er of roughly 55dB for a duration of 76 ± 8 mS. A guided
wedge at an ultrasonic power level of 64 dB can be used
for the 0.7 mil wire. The recommended wire bond stage
temperature 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 die with vacuum on die
center.)
This MMIC is also static sensitive and ESD handling pre-
cautions 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.
