IPC 7711A.pdf - 第23页

1.7 Basic Considerations 1. Appr opriate Appr ovals Appropriate approvals should be obtained before pro- ceeding with PC board modiﬁcation, rework or repair . Such approvals should include agreements as to accep- tance c…

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

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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

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preferably a lightweight, high quality, EOS/ESD con-

trolled motorized rotary tool. This tool can be used for

detailed work (i.e., solder resist and conformal coating

removal, grinding out burns or laminate defects, drill-

ing out plated holes, cutting ﬁne pitch conductors etc.).

9. Precision Drill/Mill System

Demanding projects often require the need to make

very precise holes, slots, groves etc.. Accurate depth

control and high speed may be required. A precision

drilling/milling system with ﬁxturing to hold the

printed board assembly and an attached microscope

may be advisable for those unusually demanding

projects.

10. Replacement Conductors and Lands

There are commercially available replacement conduc-

tors and lands that are normally fabricated from cop-

per foil and plated with solder or nickel and gold for

edge contact repair. These conductors and lands are

available with or without a dry ﬁlm adhesive on the

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.

11. 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.

12. 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.

13. Eyelets and Eyelet Press System

Solder plated copper eyelets and an eyelet press/setting

tool to repair damaged plated through holes may be

required.

14. 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.

15. 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.

16. 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.

17. Materials

The materials listed are ‘‘generic’’ in nature. It is rec-

ommended that these materials are available or

approved by your company. The use of certain materi-

als includes some increased risk (ﬁre, personnel safety,

etc.) and such materials should not be used unless

appropriate safety precautions are enforced.

1.9 Process Goals and Guidelines In the three basic

processes of Component Removal, Land Preparation

and Component Installation/Replacement, the funda-

mental Process Goals and Guidelines are as follows:

Non-destructive Process — During any assembly or rework

process, no damage or degradation should occur to the

board (both substrate and circuit elements), adjacent com-

ponents, and the component to be installed or removed.

This damage may be either mechanical, thermo/mechanical

or purely thermal in nature and may result in either imme-

diate failure, degradation in performance over time (latent

failure) or a reduction in reliability.

EOS/ESD damage must also be avoided by employing

proper work procedures, work stations and equipment con-

trols.

Controllable, Reliable and Repeatable Process — The pro-

cess can be employed, and when necessary, modiﬁed by a

trained operator in a repetitive fashion with consistently

acceptable results.

Process Appropriate to Particular Application — The pro-

cess (or modiﬁcation thereof) employed is appropriate to

the particular application based on the relevant guidelines

described below.

October 2003 IPC-7711A/7721A

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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