Bonding, Handling, and Mounting Procedures for

Chip Diode Devices

M/A-COM Products

Rev. V3

Application Note

M541

5

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Reliability Problems

Silver conductive epoxies should not be used where they

will come into contact with lead tin solders or high tin

solder. There can be an anodic reaction which may

cause failure of the bond.

Bond Strength

The shear bond strength of good epoxy joint can ap-

proach that of solder 50-100Kgms/cm

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 cleanliness.

Thermal Resistance

Although the thermal resistance of silver conductive ep-

oxy bonds is a little higher than that of gold tin eutectic

solder, it is still satisfactory for all but the highest power

applications as long as the epoxy is kept thin.

Visual Inspection

Die down bonds should be checked regularly using a 5-

15X microscope and should meet visual criteria shown in

table 2.

Top Bonding to the Chip

Most chips can be bonded with a wedge bonder. The

size and shape of the contact will depend on the size of

the bonding pads and the parasitic inductance or capaci-

tance requirement of the circuit.

A gold strap is effective for the majority of applications.

Critical criteria in this procedure are cleanliness, bonding

tip shape, tip pressure, and stage temperature.

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 equipment

available. Table 3 illustrates some suggested top bond-

ing methods listed by type of the chip and circuit applica-

tions. Usually the simplest contacts are gold strap 0.001

X 0.005 inch or a 0.0007 to 0.001 inch diameter wedge

bonded gold wire. The inductance of a 1 mil diameter

wire will be ~ 0.05 nH for a 0.20 inch long lead. This in-

ductance can be reduced considerably by using multiple

contact wires or by using straps (a technique which also

increases reliability).

Selection of Bonding Equipment Tools & Tips

The choice of bonding equipment and tools depends

greatly on the type of circuit and chips to be used. Most

bonding equipment manufactures have useful literature

available.

Wire Bonding

It is very difficult to give definite parameter values of

force pressure time and temperature for an optimum

bonding schedule. Different wires or strap sizes, bonding

surfaces or semiconductor die characteristics require

different bonding conditions. In general, the bonding pa-

rameters should be adjusted to maximize reproducibility

at a high bond pull strength.

Most problems are caused by improper bonding machine

and tool settings as well as improper maintenance and

cleanliness. It is important to control the movement of the

part being bonded, alignment of tools, tool height, angle,

and tool condition.