Bonding, Handling, and Mounting Procedures for

Chip Diode Devices

M/A-COM Products

Rev. V3

Application Note

M541

1

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Discussion

Chip Diode devices for use in integrated circuits and

hybrid integrated circuits have proliferated in the last few

years. Today circuit designer is faced with a multiplicity

of alternatives in the involving tradeoffs of particular ad-

vantages and disadvantages. The obvious advantages in

the use of chip diodes in hybrid integrated circuit applica-

tions are their very small size and potentially lower cost.

Small size and simplicity of structure give the benefit of

minimal parasitics, but as the size of the diode becomes

smaller, handling and production problems increase. By

outlining our conclusions, we hope to help the designer

overcome some of the difficulties encountered when

using chips in MIC applications. M/A-COM Tech manu-

factures a large selection of chip and packaged diodes

for hybrid integrated circuits. Obviously not all diode

types are available in all configurations. Characteristics

such as breakdown voltage or capacitance may limit the

size of the chip or its form.

Silicon Chip Devices

CERMACHIP™ PIN Diodes

Oxide Passivated PIN Chips

Beam Lead PINs

Snap Varactor Chips

Tuning Varactor Chips

MNS Chip Capacitors

Schottky Chips

Beam Lead Schottky Diodes

PF transistor Chips (Low Noise)

Silicon Chip Devices

Gunn Diodes

GaAs Tuning Varactors

Beam lead GaAs Tuning Varactors

GaAs Multipliers

GaAs Schottky Mixers

GaAs Abrupt and Hyperabrupt Tuning Varactors

GaAs Beam lead Schottky

Microstrip Packages and Chip Carriers

Chip diodes usually require specialized equipment for die

attachment to the circuit and for wire or strap bonding to

the top of the chip. These operations require a clean

work environment and special handling equipment such

as vacuum pickups, hot gas bonders and/or thermal

compression bonding equipment.

Not all MIC circuits require chips. In many cases

(especially for conventional stripline circuits) a hybrid

circuit package or carrier will give satisfactory results and

can be handled much more easily without a large invest-

ment in fabrication equipment. M/A-COM Tech supplies

a broad band of diodes in stripline or carrier packages.

Chip Bonding Methods

The biggest problem in using chip diodes is the damage

encountered when assembling chips into circuits. In gen-

eral, the value of the integrated circuits far exceeds the

cost of the chip itself. When packaged diodes are used,

the critical die attach and top contract operations are per-

formed by M/A-COM tech and all devices are RF tested

after assembly into the package. When the circuit fabrica-

tor performs the die attach and wire bonding operation on

a complex substrate, he /she runs the risk of losing or

damaging a chip during the bonding operation which can

results in the loss of the whole circuit or in an expensive

rework cycle.

The most common problems that arise when bonding

chips to the circuit are: the introduction of excessive series

resistance, especially under forward bias conditions due to

the improper bonding of the chip to the ground plane; poor

reliability due to the entrapment of fluxes under the bond;

and mechanical failure of the bond under thermal shock or

temperature cycling. All three conditions are the results of

improper wetting of the die to the ground plane and are

usually caused by inadequate cleanliness or inadequate

bonding conditions,

The Influence of the Circuit Board on

Chip bonding Methods

Selection of the chip bonding method must take into con-

sideration the characteristics of the circuit board material

being used.

Stripline teflon fiberglass circuits should be soft soldered.

Most eutectic solders melt at temperatures too high (250-

300ºC) to be used with teflon fiberglass boards. Conduc-

tive epoxies can also be used, but the results may not be

reliable. The use of Gunn diodes on teflon fiberglass cir-

cuits is not recommended because the major problem in

operating these diodes is removal of heat. It is absolutely

essential that eutectic solders or thermal compression

bonding be used to bond these diodes to achieve the best

thermal resistance. Soft solders and conductive epoxies

are not acceptable methods for bonding Gunn diodes. The

use of beam lead diodes with teflon fiberglass boards is

not generally recommended. Because these boards are

flexible, they may bend during or after bonding and cause

the diode leads to break.

In many cases conductive epoxies will give good results

with little or no complex equipment required. Although the

high temperature and long them reliability of this type of

band is not generally as good as eutectic solder, the use

of conductive epoxies is an acceptable and sample way to

fabricate most circuits.