Bonding, Handling, and Mounting Procedures for

Chip Diode Devices

M/A-COM Products

Rev. V3

Application Note

M541

2

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Soft solders, such as the eutectic composition of antimony

or lead tin, give excellent reliability and good high tem-

perature characteristics. The use of flux for soldering is

not recommended at any time. Instead, a cover gas such

should be used. When applicable, probably the best die

down procedure is an ultrasonic silicon gold thermal com-

pression bond or a high temperature eutectic solder (such

as gold tin eutectic– 80% Au, 20% Sn) with a melting

point of approximately 280ºC.

Chip Die Down Bonding Techniques

Hot Gas Bonding of Chips

The hot gas bonder is one of the most convenient ways of

bonding chips onto a metal ground plane or circuit. Both

silicon and GaAs may be bonded using similar tech-

niques.

GaAs is brittle and softer than silicon. The use of gold tin

solder perform (80% Au, 20% Sn) with an eutectic melting

point of 280ºC is recommended. A clean, gold plated sur-

face is required to insure good wetting. The perform

should be large enough to insure that the die fits within

the area shown. The perform should be ~1 mil thick.

temperature at the tip should be approximately 400ºC.

The wetting time after the solder reflow is critical for

strong bonding. It should be carefully controlled; 3 sec ± 1

sec. If done correctly, the shear strength of a 10 X 10 mil

die will average 250-300 grams.

Ribbon and Wire Attachment

It is recommended that thermo-compression bonding be

used. The bonding tip should be smaller than the anode

contact. The exact conditions will depend on the tool

types used. It is recommended that a half hard gold wire

or strap be used. The wire or strap diameter should be

smaller than the diameter of the anode contact. Typical

bonding force should be 20 to 15 grams, and should not

exceed 30 grams. When wire bonding, a thermal com-

pression wedge bonder is recommended using a heated

stage and heated tip. The stage temperature should be ~

240ºC ± 10ºC and the recommended temperature for the

tip is 120ºC. Ultrasonic scrubbing is not recommended.

Furnace Solder of Dice

A moving belt furnace is also an excellent method for sol-

dering chips. A belt furnace with an 80-20 forming gas

atmosphere and nitrogen curtains on the ends of the fur-

nace is recommended. All parts should be clean and free

of oil and grease.

The temperature and speed of the belt should be adjusted

so that the parts reach ~ 25-50ºC over the melting point of

solder for a period of 2 to 5 minutes. Adequate tooling and

furnace temperatures are usually necessary to obtain

good alignment. “Clean” gases are also very important.

The criteria for acceptable solder die is shown on the fol-

lowing page.

Die Down

Method

Resultant

Thermal

Resistance

Temperature

Required

High

Temperature

Capabilities

Power

Handling

Capability

Ease of

Operation

Special

Equipment

Required

Potential

Problems

Conductive

Epoxy

Good with

proper

technique

Room temp to

150˚C

Good

Low to

medium power

Easiest to

apply

Little to none

High series or thermal

resistance

Soft solder i.e.,

Pb-Sn-Ag

(90,5,5)

Pb-Sn (60,40)

Good to very

good

200 - 280˚C

180 - 200˚C

Good

Good to very

good for low or

high power

Simple

application

Heated stage

hot gas bonder

or gas curtain

and furnace

Flux is usually required

with lead solders.

Cleaning of flux must

be done carefully

Eutectic Solder

Au-Sn (80,20)

Sn-Sb (97,3)

Very good

Approx. 300˚C

Approx. 230˚C

Good

Very good

Simple

application

Heated stage

or hot gas

bonder

Needs clean reducing

atmosphere

Gold silicon

Eutectic

(Thermal Com-

pression Bond)

Very good

Approx. 380˚C

Good

Very good

Most difficult

Ultrasonic

bonder with

heated stage &

tip preferable

Cleanliness, proper

bonding conditions

CHIP

SOLDER PREFORM