Bonding, Handling, and Mounting Procedures for

Millimeterwave PHEMT MMIC’s

M/A-COM Products

Rev. V4

Application Note

M570

3

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is considering for development. Performance is based on target specifications, simulated results,

and/or prototype measurements. Commitment to develop is not guaranteed.

PRELIMINARY: Data Sheets contain information regarding a product M/A-COM Technology

Solutions has under development. Performance is based on engineering tests. Specifications are

typical. Mechanical outline has been fixed. Engineering samples and/or test data may be available.

Commitment to produce in volume is not guaranteed.

Curing of the epoxy should follow the manufacturer’s

recommended schedule. They epoxy must be cured in

air or oxidizing atmosphere since the reaction requires

oxygen.

The epoxy oven should be clean and have

good air flow. The epoxy will not cure well if there are

other solvent fumes in the atmosphere.

The carrier fluid must not be allowed to flow on the top of

the chip. Not only will it make the chip un-bondable, it

will be almost impossible to detect under normal bonding

procedure.

If a vacuum tip is used to put the chip in

place, remove the vacuum when the chip is 10 mils from

the epoxy. Static charge will hold the chip to the tip. If

the vacuum tip touches the epoxy, it will become coated

with the epoxy carrier fluid and contaminate the next

chip.

This same problem may occur with the use of

tweezers. The tweezers should be cleaned before pick-

ing up another chip if they touch the epoxy.

The shear bond strength of a good epoxy joint can ap-

proach that of solder 50-100 kgms/cm2. The thickness

of the conductive epoxy should be kept at 0.001” or less.

The shear bond strength should be about:

40-60 grams for 0.010 x 0.010 inch chip

150-250 grams for 0.020 x 0.020 inch chip

350-500 grams for 0.030 x 0.030 inch chip

In general, the epoxy will shear before the chip breaks.

Weak bonds are usually caused by the use of old epoxy,

bonds that are too thick, or lack of cleanliness.

Visual Inspection

Die down bonds should be checked with a 5-15X micro-

scope and should meet the visual criteria shown in Table

2.

Top Contacting Methods

The usual criteria for choosing a specific top bonding

technique are the size of the top contact of the chip, the

type of chip, the sensitivity of the chip to temperature

and pressure, the type of circuit board, and the equip-

ment available. Usually, the simplest contacts are a gold

0.0007 to 0.001 inch diameter wedge bonded gold wire.

The inductance of a 1 mil diameter wire will be ~0.5 nH

for a 0.20 inch long lead.

This inductance can be re-

duced considerably by using multiple contact wires.

It is very difficult to give definite parameter values of

force pressure time and temperature for an optimum

bonding schedule. Different wire, bonding surfaces, or

die characteristics require different bonding conditions.

GaAs is very brittle and extra care should be taken when

wire bonding. In general, the bonding parameters should

be adjusted to maximize reproducibility at a high bond

pull strength.

Die Down Method

Visual

(Good Bond Criteria)

Typical Bond Strength

(In Stress)

Extra RS1 From Die Down

(0.020” Chip)

Conductive Epoxy

Flat, maximum epoxy thickness

approx. 0.001 inch 90% min. wetting

Approx. 50-100 kgms/cm2

Less than 0.1 ohms

Soft Solder

Flat, maximum epoxy thickness

approx. 0.001 inch 90% min. wetting

Approx. 70-100 kgms/cm2

Less than 0.1 ohms

Gold-tin Eutectic Solder

Flat, maximum epoxy thickness

approx. 0.001 inch 90% min. wetting

Approx. 100-150 kgms/cm2

Less than 0.1 ohms

1. This is the approximate extra RF series resistance from an ideal lossless bond of a 0.020” x 0.020” chip.

Table 2. Visual Inspection for Good Die-Down Bonds (Using a 5-15x Microscope)