Bonding, Handling, and Mounting Procedures for

Chip Diode Devices

M/A-COM Products

Rev. V3

Application Note

M541

6

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In general, the die will crack or “crater” if too hard a wire

or excessive pressure is used. Too little pressure results

in small, weak bonds.

A good wire bond should be stronger then the wire and

should also be two or three times the wire diameter as

illustrated.

Also illustrated are drawings of another type of wire

bond, the ball bond, As with all top bonds to planar die,

the wire (or strap) should break during a pull test before

the bond breaks.

When wire bonding, the deformed width of the wire

should be about 1.3 to 1.8 times the wire thickness as

shown in the wire bond sketch below.

If the deformed width is too small, the bond will tend to

lift off. If it is too large (greater than 1.8 times the wire

diameter) the wire tends to weaken and break.

Also shown is a curve of the pull strength vs deformed

width of ultrasonic bonded wire.

Wire Bonding to GaAs Junctions

GaAs is very brittle, and although the above mentioned

procedures apply, the following extra precautions should

be taken when wire bonding.

Wire bonds to the junctions are best made using a ther-

mal compression wedge bonder with a heated stage and

tip. A stage temperature of 240ºC and a tip temperature

of 120ºC is recommended. Typical bonding force should

be the region of 20 grams for the smallest junctions but

less than 40 grams for all others junctions. It is recom-

mended that dead soft gold wire be used with a diameter

of

0.0007 inches for the smallest mesa and 3 mil X

0.0005 ribbon for the largest mesa and 50 ohms attach-

ment. For GaAs diodes, such as PIN diodes in parallel

configuration, two ribbons are preferable.

Strap Bonding

When bonding a strap, the bond should not deform the

strap by more than 50%. The tool and conditions should

be selected to provide a bond that has at least the same

cross sectional area as the strap itself. For example, a

0.5 mil x 5 mil strap should have a bond cross section of

2.5 mils square or greater. The schematic shown illus-

trates a typically strong single strap bond to a large

mesa. Cross strapping is used for low parasitic induc-

tance. Careful heat and pressure control must be exer-

cised in order to form a strong, damage free cross strap

bond.