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Mounting & Bonding Techniques for Millimeterwave GaAs MMICs

The die should be attached directly to the ground plane eutectically or

with conductive epoxy (see HMC general Handling, Mounting, Bonding

Note).

50 Ohm Microstrip transmission lines on 0.127mm (5 mil) thick alumina

thin film substrates are recommended for bringing RF to and from the chip

(Figure 1). If 0.254mm (10 mil) thick alumina thin film substrates must be

used, the die should be raised 0.150mm (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 0.102mm (4 mil) thick die to a 0.150mm (6 mil) thick

molybdenum heat spreader (moly-tab) which is then attached to the

ground plane (Figure 2).

Microstrip substrates should brought as close to the die as possible in

order to minimize bond wire length. Typical die-to-substrate spacing is

0.076mm to 0.152 mm (3 to 6 mils).

An RF bypass capacitor should be used on the Vdd input. A 100pF single

layer capacitor (mounted eutectically or by conductive epoxy) placed no

further than 0.762mm (30 Mils) from the chip is recommended.

Handling Precautions

Follow these precautions to avoid permanent damage.

Storage:

All bare die are placed in either Waffle or Gel based ESD

protective containers, and then sealed in an ESD protective bag for

shipment. Once the sealed ESD protective bag has been opened, all die

should be stored in a dry nitrogen environment.

Cleanliness: Handle the chips in a clean environment. DO NOT attempt

to clean the chip using liquid cleaning systems.

Static Sensitivity:

Follow ESD precautions to protect against ESD

strikes.

Transients: Suppress instrument and bias supply transients while bias is applied. Use shielded signal and bias

cables to minimize inductive pick-up.

General Handling: Handle the chip along the edges with a vacuum collet or with a sharp pair of bent tweezers. The

surface of the chip has fragile air bridges and should not be touched with vacuum collet, tweezers, or fingers.

Mounting

The chip is back-metallized and can be die mounted with AuSn eutectic preforms or with electrically conductive epoxy.

The mounting surface should be clean and flat.

Eutectic Die Attach: A 80/20 gold tin preform is recommended with a work surface temperature of 255 °C and a

tool temperature of 265 °C. When hot 90/10 nitrogen/hydrogen gas is applied, tool tip temperature should be 290 °C.

DO NOT expose the chip to a temperature greater than 320 °C for more than 20 seconds. No more than 3 seconds of

scrubbing should be 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 once it is placed into position. Cure epoxy per the manufacturer’s schedule.

Wire Bonding

Ball or wedge bond with 0.025mm (1 mil) diameter pure gold wire (DC Bias) or ribbon bond (RF ports) 0.076mm

x 0.013mm (3 mil x 0.5 mil) size is recommended. Thermosonic wirebonding with a nominal stage temperature of

150 °C and a ball bonding force of 40 to 50 grams or wedge bonding force of 18 to 22 grams is recommended. Use

the minimum level of ultrasonic energy to achieve reliable wirebonds. Wirebonds should be started on the chip and

terminated on the package or substrate. All bonds should be as short as possible <0.31mm (12 mils).

0.102mm (0.004”) Thick GaAs MMIC

Ribbon Bond

RF Ground Plane

0.127mm (0.005”) Thick Alumina

Thin Film Substrate

0.076mm

(0.003”)

Figure 1.

0.102mm (0.004”) Thick GaAs MMIC

Ribbon Bond

RF Ground Plane

0.254mm (0.010”) Thick Alumina

Thin Film Substrate

0.076mm

(0.003”)

Figure 2.

0.150mm (0.005”) Thick

Moly Tab

HMC263

v04.0907

GaAs MMIC LOW NOISE

AMPLIFIER, 24 - 36 GHz