Bonding, Handling, and Mounting Procedures for

Chip Diode Devices

M/A-COM Products

Rev. V3

Application Note

M541

8

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Bonding Beam Lead Diodes

Selection of the beam lead bonding method must take

into consideration the characteristics of the circuit board

material used. Hard substrates such as alumina and

quartz are recommended. Various bonding techniques

are described below and may all be used on hard sur-

faces.

The beam lead diode is a silicon chip with planar gold

leads which extend from the top surface of the chip

(~0.010 to 0.030 inches). Beam lead diodes are gener-

ally the smallest size chips available. They must be han-

dled with care because the leads may easily be distorted

or broken by the normal pressure of tweezers handling.

Most vacuum tips are too large. A vacuum pencil with a

#27 tip is recommended. A pointed wooden stick such as

a sharpened Q tip or toothpick which has been dipped in

isopropyl alcohol can also be used as a pick and place

tool since the beam lead will adhere to the moistened

point. This work should be performed under 10X to 30X

magnification.

Beam lead diodes are easily damaged by static electric-

ity and/ or current from a small low impedance ground

loop in the circuit. When mounting the diode in the cir-

cuit , contact should never be made across the gap. A

static discharge from the operator may flow through the

diode and destroy it. The circuit should always be

grounded before the second lead of the diode is at-

tached.

The preferred methods for bonding a beam lead diode

are thermal compression bonding and parallel gap weld-

ing. For thermal compression bonding, the beam lead

diode is placed down (gold beam to gold plated sub-

strate) with the leads resting flat on the pad and the bond

made by using a heated wedge. Heat and pressure form

a metallurgical bond. A minimum of 100 microinches of

gold on the substrate is recommended for optimum

bonding.

In the parallel gap technique, current is first passed

through the substrate metallization, then through the

device lead. Most of the heat is generated at the inter-

face. Extreme care must be taken to see that the step

welder does not discharge through the diode junction, or

the diode will be destroyed. The bonding pressure should

be ~ 900 gms / mm

The major advantage of the parallel gap technique is that

a cold ambient may be used. Heat is only generated in

the vicinity of the bond itself. Caution must be taken

when making the second bond because if the diode is

placed in tension, the leads may break.