M570 Datasheet, PDF (1/4 Pages) M/A-COM Technology Solutions, Inc. – Bonding, Handling, and Mounting Procedures for Millimeterwave PHEMT MMIC’s

Application Note
M570
Bonding, Handling, and Mounting Procedures for
Millimeterwave PHEMT MMIC’s
M/A-COM Products
Rev. V4
Discussion
Millimeterwave MMIC's are becoming more common in
commercial applications. Their small size and potentially
lower cost has made them valuable in the growing mar-
ket of millimeterwave systems. Their size and delicate
nature also makes them fragile. The following informa-
tion is provided to help die users handle, mount, and
bond MMIC chips.
It should be noted that MMIC's usually require special-
ized equipment for die attachment and bonding. These
operations require a clean environment and special han-
dling equipment such as vacuum pickups, hot gas bond-
ers and/or thermal compression and/or thermo-sonic
bonding equipment.
M/A-COM Tech offers a family of GaAs MMIC amplifiers
above 15 GHz. This note addresses:
die attach and top contact operations are performed by
M/A-COM Tech and all devices are RF tested after assem-
bly into the packages. When the circuit fabricator performs
the die attach and wire bonding operation on a complex
substrate, he/she runs the risk of losing or damaging a chip
during the bonding operation which can result in the loss of
the whole circuit or in an expensive rework cycle.
The most common issues that arise when bonding MMIC's
to the circuit are: the introduction of excessive series resis-
tance, especially under forward bias conditions due to the
improper bonding of the chip to the ground plane; poor reli-
ability due to the entrapment of contaminates under the
bond; and mechanical failure of the bond under thermal
shock or temperature cycling. All three conditions are the
result of improper wetting of the die to the ground plane and
are usually caused by inadequate cleanliness or inadequate
bonding conditions.
GaAs MMIC Devices
Low Noise Amplifiers
Power Amplifiers
Gain Blocks
Driver Amplifiers
Handling and Assembling of Chips and
Circuits
The challenges of handling and assembling chips into
packages can be best separated into two areas: putting
the chip into the circuit (die down) and making top con-
tact to the chip (top bonding).
Permanent damage to the MMIC may occur if the pre-
cautions are not followed. The MMIC's should be han-
dled in a clean room type of environment. All devices
are static sensitive, so handling equipment and person-
nel should comply with DOD-STD-1686 Class I. Avoid
instrument and power supply transients while bias is
connected to the MMIC. Use shielded signal and bias
cables to minimize inductive pick-up. In general, DO
NOT touch the surface of the die. It is recommended
that the MMIC die be handled with vacuum pick-up tools
with rubber or soft material or handled along the long
side with tweezers.
Chip Bonding Methods
A recommendation for improved bonding is to plasma
clean the carrier before any eutectic is used. The MMIC
should be plasma cleaned before wire bonding.
Table 1 provides helpful information in the selection of die
down techniques.
Chip Die Down Bonding Techniques
Eutectic Bonding of Chips - Power Amps
The eutectic bonder is one of the most convenient ways of
bonding chips onto a metal ground plane or circuit. Both
silicon and GaAs chips may be bonded using similar tech-
niques.
GaAs power die are back metallized with Ti/Au metalliza-
tion. The use of gold tin solder perform (80% Au, 20% Sn)
with an eutectic melting point of 295 ± 5˚C is recommended.
A clean, flat, gold plated surface is required to insure good
wetting. The preform should be large enough to insure that
the die fits within the areas shown, should be ~1 mil thick,
and should be 10% smaller than the die itself. During the
attaching process, the die collet should be “scrubbed,”
rubbed into the eutectic, to ensure a good die attach. The
carrier of package temperature and collet temperature
should be 295 ± 5˚C. There should be a 90/10 nitrogen/
hydrogen gas applied to the bonding surface. When the
forming gas is applied ensure that the bonding surface tem-
perature does not fall below the recommended temperature.
This should be done only for the die. All other components -
50W lines, caps, resistors - should be done with electrically
conductive epoxy. DO NOT expose the die to a tempera-
ture greater than 320˚C for more than 20 seconds.
A risk in using MMIC's is the possible damage incurred
when assembling chips into circuits. In general, the
value of the MMIC circuits exceeds the cost of the MMIC
chip itself. When packaged MMIC's are used, the critical
1
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