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back. Adhesive backed conductors and lands are nor-

mally heat bonded to the board surface. Replacement

conductors and lands are available in hundreds of dif-

ferent shapes.

Compatible replacement conductors and features may

also be salvaged from scrap printed wiring boards, if

necessary.

10. Gold Plating System

Plating gold edge contacts or any metal surface

requires the use of materials that may have environ-

mental and safety concerns and must be handled prop-

erly. The power applied to the plating surfaces must be

controlled accurately to expect reliable results. A good

plating systems should include; a DC power supply

with voltage and current meters, plating anodes sized

for gold edge contact plating, a solution tray to collect

the solution runoff, a support for the PC board and a

tray to hold and store the various chemicals safely.

11. Epoxy and Coloring Agents

Many repair operations require the use of high

strength, high temperature epoxies. For high tempera-

ture applications two-part epoxies offer the highest

strength, thermal resistance and durability. It may also

be important to have resists or coloring agents so that

you can restore the cosmetic appearance of the board.

It is best to cure the epoxies in an oven if possible.

12. Eyelets and Eyelet Press System

Solder plated copper eyelets and an eyelet press/setting

tool to repair damaged plated through holes may be

required.

13. Cleaning Station/System

Regardless of the Class of Product serviced, a cleaning

system that is chemically matched to the ﬂux sys-

tem(s) in use will be essential to a satisfactory repair.

In organizations that perform procedures on Class 3

Products, it may also be necessary to have a cleanli-

ness test system in order to periodically evaluate the

ability of the cleaning system to meet the

requirements/expectations of the user. Interim or

in-process cleaning at the workstation should be used

pending completion of the procedure and the ﬁnal

cleaning.

14. Tools and Supplies

Also needed are a wide assortment of hand tools

including tweezers, various pliers, ﬁles, dental picks,

cutting tools and materials such as ﬂuxes, solders, and

other common items.

15. Conformal Coating Area

The cost, safety concerns and utility services (air

pressure/vacuum, power, venting, UV illuminations,

etc.) of equipment associated with both the removal

and application of conformal coating suggest to many

organizations that one central conformal coating and

encapsulant area be installed.

February 1998 IPC-7721

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IPC-7721 February 1998

OUTLINE

Electrostatic Discharge (ESD) is the rapid discharge of electri-

cal energy that was created from static sources. When the

electrical energy is allowed to come in contact with or even

close to a sensitive component it can cause damage to the

component. Electrostatic-Discharge Sensitive (ESDS) compo-

nents are those components that are affected by these high

energy surges. The relative sensitivity of a component to ESD

is dependent upon its construction and materials. As compo-

nents become smaller and operate faster, the sensitivity

increases.

Electrical Overstress (EOS) is the internal result of a unwanted

application of electrical energy that results in damaged com-

ponents This damage can be from many different sources,

such as electrically powered process equipment or ESD

occurring during handling or processing.

ESDS components can fail to operate or change in value as a

result of improper handling or processing. These failures can

be immediate or latent. The result of immediate failure can be

additional testing and rework or scrap. However the conse-

quences of latent failure are the most serious. Even though

the product may have passed inspection and functional test,

it may fail after it has been delivered to the customer.

It’s important to build protection for ESDS components into

circuit designs and packaging. However, in the manufacturing

and assembly areas, we often work with unprotected elec-

tronic assemblies that are attached to the ESDS components.

This section will be dedicated to safe handling of these unpro-

tected electronic assemblies.

For that purpose, the following subjects are addressed:

2.1.1 Electrical Overstress (EOS) Damage Prevention

2.1.2 Electrostatic Discharge (ESD) Damage Prevention

2.1.2.1 Warning Labels

2.1.2.2 Antistatic Materials

2.1.3 Anti-Static Work Station

2.1.4 Physical Handling

Information in this specification is intended to be general in

nature. Additional detailed information can be found in EIA-

625, Requirements for Handling Electrostatic-Discharge-

Sensitive (ESDS) Devices

2.1.1 Electrical Overstress (EOS) Damage Prevention

Electrical components can be damaged by unwanted electri-

cal energy from many different sources. This unwanted elec-

trical energy can be the result of ESD potentials or the result

of electrical spikes caused by the tools we work with, such as

soldering irons, soldering extractors, testing instruments or

other electrically operated process equipment. Some devices

are more sensitive than others. The degree of sensitivity is a

function of the design of the device. Generally speaking higher

speed and smaller devices are more susceptible than their

slower, larger predecessors. The purpose or family of the

device also plays an important part in component sensitivity.

This is because the design of the component can allow it to

react to smaller electrical sources or wider frequency ranges.

With todays products in mind, we can see that EOS is a more

serious problem than it was even a few years ago. It will be

even more critical in the future.

When considering the susceptibility of the product we must

keep in mind the susceptibility of the most sensitive compo-

nent in the assembly. Applied unwanted electrical energy can

be processed or conducted just as an applied signal would be

during circuit performance.

Before handling or processing sensitive components, tools

and equipment need to be carefully tested to ensure that they

do not generate damaging energy, including spike voltages.

Current research indicates that voltages and spikes less than

0.5 volt are acceptable. However, an increasing number of

extremely sensitive components require that soldering irons,

solder extractors, test instruments and other equipment must

never generate spikes greater than 0.3 volt.

As required by most ESD specifications including EIA-625,

periodic testing may be warranted to preclude damage as

equipment performance may degrade with use over time.

Maintenance programs are also necessary for process equip-

ment to ensure the continued ability to not cause EOS dam-

age.

EOS damage is certainly similar in nature to ESD damage,

since damage is the result of undesirable electrical energy.

2.1.2 Electrostatic Discharge (ESD) Damage Prevention

The best ESD damage prevention is a combination of prevent-

ing static charges and eliminating static charges if they do

Product Class: R, F, C, W

Skill Level: Intermediate

Level of Conformance: High

7721

Repair and Modification of

Printed Boards and Electronic Assemblies

Revision:

Date: 2/98

Handling Electronic

Assemblies

Number: 2.1

Material in this manual was voluntarily established by Technical Committees of the IPC. This material is advisory only and its

use or adaptation is entirely voluntary. IPC disclaims all liability of any kind as to the use, application, or adaptation of this

material. Users are also wholly responsible for protecting themselves against all claims or liabilities for patent infringement.

Equipment referenced is for the convenience of the user and does not imply endorsement by the ipc.

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