HMC-AUH312 Data Sheet
Rev. E | Page 16 of 17
MOUNTING TECHNIQUES
Attach the die directly to the ground plane eutectically or with
conductive epoxy.
Using 50 Ω microstrip transmission lines on 0.127 mm (5 mil)
thick alumina thin film substrates is recommended for bringing
the RF to and from the chip (see Figure 26). If 0.254 mm
(10 mil) thick alumina thin film substrates must be used, raise the
die 0.150 mm (6 mils) so that the surface of the die is coplanar
with the surface of the substrate. One way to accomplish this is
to attach the 0.100 mm (4 mil) thick die to a 0.150 mm (6 mil)
thick molybdenum heat spreader (moly tab), which is then
attached to the ground plane (see Figure 27).
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).
Figure 26. Routing RF Signals
Figure 27. Routing RF Signals Using Molly Tab
The chip is back-metallized and can be die mounted with AuSn
eutectic preforms or with electrically conductive epoxy. Ensure
that the mounting surface is clean and flat.
Eutectic Die Attach
An 80% gold/20% tin preform is recommended with a work
surface temperature of 255°C and a tool temperature of 265°C.
When hot 90% nitrogen/10% hydrogen gas is applied, make
sure that the tool tip temperature is 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
Apply a minimum amount of epoxy to the mounting surface so
that a thin epoxy fillet is observed around the perimeter of the
chip when it is placed into position. Cure the epoxy per the
schedule provided by the manufacturer.
WIRE BONDING
RF bonds made with two 1 mil wires are recommended. These
bonds must be thermosonically bonded with a force of 40 g to 60 g.
Use of dc bonds of 0.001 inch (0.025 mm) diameter, thermosoni-
cally bonded, are recommended. Create ball bonds with a force
of 40 g to 50 g and wedge bonds at 18 g to 22 g.
Create all bonds with a nominal stage temperature of 150°C.
Apply a minimum amount of ultrasonic energy to achieve
reliable bonds. Keep all bonds as short as possible, less than
12 mil (0.31 mm).
RF GROUND PLANE
0.100mm (0.004") THICK GaAs MMIC
WIRE BOND
0.127mm (0.005") THICK ALUMINA
THIN FILM SUBSTRATE
0.076mm
(0.003")
13476-025
RF GROUND PLANE
0.100mm (0.004") 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")
13476-026
