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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 be brought as close to the die as possible in order to

minimize bond wire length. Typical die-to-substrate spacing is 0.076mm (3 mils).

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 > ± 250V 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 0.025 mm (1 mil) diameter pure gold wire 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 <0.31 mm (12 mils).

0.102mm (0.004”) Thick GaAs MMIC

Wire 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

Wire 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

v02.0209

HMC565

GaAs PHEMT MMIC LOW NOISE

AMPLIFIER, 6 - 20 GHz