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3.0 Die Attach Procedure
Different die attach procedures are used for silicon chips and GaAs
devices. To die attach a silicon chip, the chip and mounting surface are
heated sufficiently for the gold of the mounting surface to mix with the
gold backside of the chip and melt into the silicon of the chip, forming
a gold-silicon eutectic bond. This technique is suitable because silicon
can tolerate the relatively high temperatures needed for eutectic
formation without endangering the silicon device.
GaAs devices are more temperature sensitive, and use instead a lower
temperature gold alloy “solderdown” technique. In both cases the die-
attach station should have the actual die attach area flooded with an
inert (forming gas or nitrogen) atmosphere.
3.1 Silicon Bipolar Transistor Die Attach Procedure
3.1.1 The heater block temperature should be 410°C ±10°.
3.1.2 Place the circuit or package into which the transistor or capacitor
will be attached on the heater block. Allow sufficient time to heat
thoroughly (5 to 15 seconds depending on thermal mass).
3.1.3 Pick up a chip with tweezers (EREM type 5 SA recommended)
and orient it properly prior to placement on the heated surface.
3.1.4 Place the chip on the heated surface and scrub with a back-and-
forth motion, being careful not to scratch the top surface of the chip.
Continue this until wetting occurs; this should take place within three
to four scrubs.
3.1.5 If wetting does not occur check that the heater block
temperature is correct and that the inert atmosphere blanket is present.
3.1.6 When wetting occurs, perform a circular scrub for one stroke to
insure wetting of the chip perimeter. Carefully remove the tweezers
from the die.
3.1.7 Remove the circuit or package from the heated surface and allow
it to cool in air.
3.2 GaAs FET Attach Procedure
3.2.1 The heater block temperature should be 300°C ±10°.
3.2.2 Place the circuit or package into which the transistor will be
attached on the heater block. Allow sufficient time to heat thoroughly
(5 to 15 seconds depending on thermal mass).
3.2.3 Pick up a Au-Sn (gold-tin) preform and place it on the circuit/
package in the die attach location. Use a sufficient quantity to insure
good wetting and to produce a fillet around the chip.