IPC 7711A - 第22页

In principle any modiﬁcation, rework or repair action taken on a product should reestablish the products original char- acter , ‘ ‘Make it like it was.’ ’ Physical changes, obvious or otherwise, can adversely af fect the…

Repairs are generally changes to an unacceptable end

product to make it acceptable in accordance with origi-

nal functional requirements. The control of repaired

products should be by means of Material Review

Board (MRB), or its equivalent, which may consist of

Design Engineering, Quality Assurance, and User rep-

resentatives. The MRB, with technical support, should

deﬁne the mutually acceptable repair method to be

used and take the action necessary to ensure that all

applicable procedures are adhered to.

Repair of a failure in the ﬁeld seldom includes an

MRB, and typically is done in accordance with a con-

tract, repair/service order or the user-activity mainte-

nance program requirements. The maximum number

of repairs per printed wiring board assembly should be

determined by the using activity or agency.

1.4.1 Classification The user of the product is respon-

sible for identifying the Class of Product. The procedure

selected for action to be taken (modiﬁcation, rework,

repair, overhaul etc.) must be consistent with the Class

identiﬁed by the user. The three Classes of Product are:

1. Class 1 – General Electronic Products

Includes products for applications where the major

requirement is the function of the completed assembly.

2. Class 2 – Dedicated Service Electronic Products

Includes products where continued performance and

extended life is required, and for which uninterrupted

service is desired but not critical. Typically, the end

use environment would not cause failures.

3. Class 3 – High Performance Electronic Products

Includes products where continued performance or

performance-on-demand is critical. Equipment down-

time cannot be tolerated, end-use environment may be

uncommonly harsh, and the equipment must function

where required, such as life support and other critical

systems.

1.4.2 Printed Board Types There are a variety of printed

board types that the procedures in this document apply to.

When selecting the appropriate modiﬁcation, rework or

repair procedure the printed board type being worked

should be considered. Select a procedure that applies to the

printed board type as listed on the procedure. Printed board

types include the following:

R. Rigid Printed Boards and Assemblies

A printed board or assembly using rigid base materials

only. These may be single-sided, double-sided or mul-

tilayered, and may be constructed from base laminate

material that spans all approved commercial grades of

laminate and includes glass fabric reinforced epoxy

and polyimide resin laminates.

F. Flexible Printed Boards and Assemblies

A printed board or assembly using ﬂexible or a com-

bination of rigid and ﬂexible materials only. May be

partially provided with electrically non-functional

stiffeners and/or cover lay. These may be single-sided,

double-sided or multilayered.

W. Discrete Wiring Boards and Assemblies

A printed board or assembly using a discrete wiring

technique to obtain electrical interconnections.

C. Ceramic Boards and Assemblies

A printed board or assembly using ceramic as the base

material with interconnections separated by dielectric.

The board layers are usually formed by alternate print-

ing or depositing of interconnections and dielectric.

The assemblies are either surface mount or die attach.

Usually multilayered, these may be single-sided or

double-sided.

1.4.3 Level of Conformance Level of Conformance pro-

vides the means for selecting an appropriate level of con-

formance to the original electrical, mechanical, physical,

environmental and visual product requirements. Each pro-

cedure lists a Level of Conformance that the product will

attain when successfully completed.

The Level of Conformance rating for each procedure is

based on the skill of the technician. The ratings are based

on long term industry experience and are not necessarily

backed up with testing data.

1.4.4 Levels of Conformance

L. Lowest Level – Signiﬁcant variance with the physical

character of the original and may vary with many of

the electrical, functional, environmental and service-

ability factors.

M. Medium Level – Some variance with the physical

character of the original and most likely varies with

some of the functional, environmental and serviceabil-

ity factors.

H. Highest Level – Most closely duplicates the physical

characteristics of the original and most probably com-

plies with all the functional, environmental and ser-

viceability factors.

Class 3 Products must use procedures rated Highest level

unless it can be demonstrated that a lower level procedure

will not adversely affect the product’s functional character-

istics.

Class 2 and 1 Products should use procedures rated High-

est level for assured safety and dependability but Medium

and Low Level procedures can be used if it has been deter-

mined that they are suitable for the speciﬁc product’s func-

tional characteristics.

Procedures in this manual are given a ‘‘Level of Conform-

ance’’ rating which is described in Table 1.

IPC-7711A/7721A October 2003

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

--``,``,-`-`,,`,,`,`,,`---

In principle any modiﬁcation, rework or repair action taken

on a product should reestablish the products original char-

acter, ‘‘Make it like it was.’’ Physical changes, obvious or

otherwise, can adversely affect the products performance or

capability factors.

1.4.5 Skill Level To assist you in determining the skill

level needed for each procedure a Skill Level indicator is

included in each process. The Skill Level recommended

should be used as a guide only. Skill levels will vary

widely from technician to technician and from company to

company. These recommendations come from industry

experience and are not necessarily backed up with substan-

tive testing. Skills are separated into three categories.

I. Intermediate – Technician with skills in basic solder-

ing and component rework but inexperienced in gen-

eral repair/rework procedures.

A. Advanced – Technician with soldering and compo-

nent rework skills and exposure to most repair/rework

procedures but lacking extensive experience.

E. Expert – Technician with advanced soldering and

component rework skills and extensive experience in

most repair/rework procedures.

1.5 Terms and Definitions For terms and deﬁnitions

refer to IPC-T-50 Terms And Deﬁnitions.

1.6 Training The quality and reliability of modiﬁed or

repaired printed boards and assemblies is highly dependent

upon the skill and competence of the person performing

these tasks. The implementation of proper methods by

unqualiﬁed personnel can result in a substandard end prod-

uct. Consequently, achieving successful results with the

methods described herein is predicated on the use of prop-

erly trained personnel whose skills have been tested and

certiﬁed to be of a sufficient level of competence.

1. Soldering Skills

Many companies have considered assembly personnel

who are competent in soldering techniques to be suffi-

ciently trained for rework/repair activities. This has

often proven to be erroneous, since proper soldering is

only one of the skills required. Also, in order to attain

comparable results, there are many instances where

component rework requires techniques that are differ-

ent than those used to originally solder the component.

2. Personnel Selection

The proper selection of trainees will contribute signiﬁ-

cantly toward the success in developing capable repair

personnel. Personnel with above average soldering

abilities and sound reasoning capabilities often make

ideal trainees. However, personnel who have no sol-

dering skills, but possess a good level of eye acuity,

manual dexterity, and sound reasoning capability, can

be successfully trained.

3. Professional Training

Companies should establish and maintain procedures

for identifying the training needs and provide for the

training of all personnel performing the activities

affecting product quality. Personnel performing spe-

ciﬁc assigned tasks shall be qualiﬁed on the basis of

appropriate education, training and experience, as

required. Appropriate records of training shall be

maintained.

a. Training for personnel and instructors is commer-

cially available and can be completed by an outside

organization specializing in the applicable disci-

pline.

b. Modiﬁcation/rework/repair training employs con-

cepts, techniques, procedures and a vocabulary that

distinguishes it from basic soldering training.

c. Effective training requires the development of high

levels of comprehension and reasoning within the

trainee. This necessitates expansive teaching meth-

ods and detailed demonstration under close instruc-

tor supervision, to help assure the development of

proﬁciency within each trainee.

Training to establish a desired level of proﬁciency can

usually be achieved after three to ten days of training,

depending on the content of the training program, the

complexity of the end product, and the proﬁciency of

the trainee. Testing and certiﬁcation can be provided

for each trainee, as the situation warrants.

Table 1 Level of Conformance

Functional Consideration

Level of Conformance

LMH

Electrical - Resistance No Verify Yes

Electrical - Inductance No Verify Yes

Electrical - Capacitance No Verify Yes

Electrical - Cross Talk No Verify Yes

Electrical - High Speed

Frequency

No Verify Yes

Environmental - Shock No Verify Yes

Environmental - Vibration No Verify Yes

Environmental - Humidity Verify Verify Yes

Environmental - Temperature Yes Yes Yes

Environmental - Altitude Verify Verify Verify

Environmental - Bacteria Verify Verify Yes

Environmental - Fungus Verify Verify Yes

Serviceability - Future Repair

or Mod.

No Yes Yes

No Procedure may not comply with functional

consideration.

Verify Procedure should comply with functional consideration

but should be tested to verify.

Yes Procedure will normally comply with functional

consideration.

October 2003 IPC-7711A/7721A

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

--``,``,-`-`,,`,,`,`,,`---

1.7 Basic Considerations

1. Appropriate Approvals

Appropriate approvals should be obtained before pro-

ceeding with PC board modiﬁcation, rework or repair.

Such approvals should include agreements as to accep-

tance criteria and limitations.

2. Singular Procedures

Procedures in this book are presented as individual

methods. Multiple procedures may be necessary to

complete the task.

3. Quality and Reliability

All attempts to modify, rework or repair printed boards

and assemblies should seek to equal the quality and

reliability of the original, unaltered, end product.

4. Procedure Selection

The procedure selected should be on the basis of opti-

mum end product functionality. Test data should be

obtained wherever possible.

5. Patience

To achieve best results, do not rush the process. Keep

in mind that most of the cost for fabrication/assembly

has already been spent, but with care and patience,

most of this cost can be salvaged.

6. Heat Application

Incorrect heat application may cause severe damage to

board materials, conductors, components, conformal

coatings and solder connections.

7. Removal of Coatings

Coating should be removed from affected areas prior

to processing. Coatings will inhibit solder removal and

adversely affect resoldering operations.

1.8 Tools and Materials Modiﬁcation, rework and repair

of PC boards and assemblies is generally a highly labor

intensive operation relying more on individual operator

skills than automation. The use of proper tools and supplies

will often have a signiﬁcant impact on the function and

reliability of the end product. To enhance the ease of the

task at hand and to improve the potential for a successful

operation, the following equipment and supplies are recom-

mended. This list should be used as a guide only.

1. Proper Workstations

A proper workstation; ESD grounded with acceptable

lighting, outlets, and conﬁgured for comfort is prefer-

able due to the degree of concentration and dexterity

required to perform high reliability PC board modiﬁ-

cation, rework and repair.

2. High Quality Microscope

Precision work generally requires a microscope. Refer

to IPC-OI-645 Standard for Visual Optical Inspection

Aids for more information.

3. Lighting

Illuminations at the surface of work stations should be

1000 Lm/m

minimum.

4. Soldering Tools

Precision soldering is important in today’s modiﬁca-

tion, rework and repair operations. Technicians may

need an assortment of special use soldering tools

appropriate to the variety of tasks at hand. These tools

must be temperature controlled, ESD/EOS safe, ergo-

nomically designed and include a selection of tips to

suit each particular operation.

5. Component Removal and Installation

Today’s expanding variety of large and small compo-

nents require an array of special use tools and methods

for safe, efficient component removal. These tools gen-

erally use either conductive heating (by contact), con-

vective heating (by hot gas) or infrared heating (by

focused infrared lamps).

Each assembly/rework method has certain advantages

and precautions depending on the particular Surface

Mount Device (SMD) (lead/terminations design, size,

body material, etc.), component mounting site (adja-

cent components, access, substrate type, thermal mass,

etc.) and the skill level of the operator.

For example, chip components addressed in this docu-

ment have different termination styles including: Bot-

tom, three or ﬁve face terminations. Therefore some

procedures depicted in this document may not be

applicable to all termination styles.

6. Preheating (Auxiliary) Heating

Preheating printed board assemblies is sometimes rec-

ommended to avoid thermal shock to temperature sen-

sitive materials and components. Preheating also

elevates the thermal mass of the assembly to allow a

rework process to proceed in an acceptable time. Pre-

heating can be accomplished using either an oven, heat

lamp, hot plate, infrared or convective style heating

system.

7. Fume Extraction

Work environments can often expose technicians to

potentially hazardous fumes. Disposal and release of

certain materials may have a signiﬁcant environmental

impact. The use of localized fume extraction systems,

environmental control devices and other personnel

protection equipment may be necessary to comply

with MSDS requirements and applicable federal, state

and local laws.

8. Hand Held Drilling and Grinding Tool

PC Board modiﬁcation, rework and repair procedures

often require drilling, milling or grinding operations.

The best type of tool for these delicate operations is

IPC-7711A/7721A October 2003

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

--``,``,-`-`,,`,,`,`,,`---