Data Sheet HMC8401
Rev. 0 | Page 15 of 17
APPLICATIONS INFORMATION
BIASING PROCEDURES
Capacitive bypassing is required for V
DD
and V
GG
1, as shown in
the typical application circuit in Figure 43. Gain control is
possible through the application of a dc voltage to V
GG
2. If gain
control is used, then V
GG
2 must be bypassed by 100 pF, 0.1 μF, and
4.7 μF capacitors. If gain control is not used, then V
GG
2 can be
either left open or capacitively bypassed as described.
The recommended bias sequence during power-up is as follows:
1. Set V
GG
1 to −2.0 V to pinch off the channels of the lower
FETs.
2. Set V
DD
to 7.5 V. Because the lower FETs are pinched off,
I
DQ
remains very low upon application of V
DD
.
3. Adjust V
GG
1 to be more positive until the desired quiescent
drain current is obtained.
4. Apply the RF input signal.
5. If the gain control function is to be used, apply to V
GG
2 a
voltage within the range of −2.0 V to +2.4 V until the
desired gain is achieved.
Use of the V
GG
2 (the gain control function) affects the drain
current.
The recommended bias sequence during power-down is as follows:
1. Turn of f the RF input signal.
2. Remove the V
GG
2 voltage or set it to 0 V.
3. Set V
GG
1 to −2.0 V to pinch off the channels of the lower
FETs.
4. Set V
DD
to 0 V.
5. Set V
GG
1 to 0 V.
Power-up and power-down sequences may differ from the ones
described, though care must always be taken to ensure adherence
to the values shown in the Absolute Maximum Ratings.
Unless otherwise noted, all measurements and data shown
were taken using the typical application circuit (see Figure 43),
configured as shown on the assembly diagram (see Figure 44)
and biased per the conditions in this section. The bias conditions
shown in this section are the operating points recommended to
optimize the overall performance. Operation using other bias
conditions may provide performance that differs from what is
shown in this data sheet. To obtain the best performance while
not damaging the device, follow the recommended biasing
sequence outlined in this section.
MOUNTING AND BONDING TECHNIQUES FOR
MILLIMETERWAVE GaAs MMICs
Attach the die directly to the ground plane eutectically or with
conductive epoxy. To bring RF to and from the chip, use 50 Ω
microstrip transmission lines on 0.127 mm (5 mil) thick alumina
thin film substrates (see Figure 42).
Figure 42. Routing RF Signals with Molytab
To minimize bond wire length, place microstrip substrates as
close to the die as possible. Typical die to substrate spacing is
0.076 mm to 0.152 mm (3 mil to 6 mil).
Handling Precautions
To avoid permanent damage, adhere to the following precautions:
All bare die ship in either waffle or gel-based ESD protective
containers, sealed in an ESD protective bag. After the sealed
ESD protective bag is opened, store all die in a dry nitrogen
environment.
Handle the chips in a clean environment. Never use liquid
cleaning systems to clean the chip.
Follow ESD precautions to protect against ESD strikes.
While bias is applied, suppress instrument and bias supply
transients. To minimize inductive pickup, use shielded
signal and bias cables.
Handle the chip along the edges with a vacuum collet or
with a sharp pair of bent tweezers. The surface of the chip
may have fragile air bridges and must not be touched with
vacuum collet, tweezers, or fingers.
Mounting
The chip is back metallized and can be die mounted with gold/tin
(AuSn) eutectic preforms or with electrically conductive epoxy.
The mounting surface must be clean and flat.
Eutectic Die Attach
It is best to use an 80% gold/20% tin preform with a work surface
temperature of 255°C and a tool temperature of 265°C. When
hot 90% nitrogen/10% hydrogen gas is applied, maintain tool tip
temperature at 290°C. Do not expose the chip to a temperature
greater than 320°C for more than 20 sec. No more than 3 sec of
scrubbing is required for attachment.
Epoxy Die Attach
ABLETHERM 2600BT is recommended for die attachment.
Apply a minimum amount of epoxy to the mounting surface so
that a thin epoxy fillet is observed around the perimeter of the
chip after placing it into position. Cure the epoxy per the schedule
provided by the manufacturer.
RF GROUND PLANE
0.05mm (0.002") THICK GaAs MMIC
WIRE BOND
0.254mm (0.010") THICK ALUMINA
THIN FILM SUBSTRATE
0.150mm
(0.005”) THICK
MOLY TAB
0.076mm
(0.003")
13850-042
