IPC 7711A - 第196页

6. TINNING Backgr ound: Once a conductor is exposed to the envi- ronment, oxidation begins to take place. The tinning of a conductor is important to ensure a quality solder con- nection. T inning stranded wire reduces th…

8.1 Splicing

1. THE PROCESS OF WIRE SPLICING IS USED IN TWO

CASES:

a. When a self-lead component (inductor, transformer,

choke, etc.) is installed (either during assembly or

as a replacement for a failed component) and,

b. In the process of repairing a damaged wire when

removal and replacement of the entire wire length

is not feasible.

2. THE FOUR MOST COMMON SPLICES USED ARE:

• Mesh Splices Mesh splices require the least wire

length in order to complete the splice and result in a

splice diameter only slightly larger than the diameter

of the wire used.

• Wrap Splices Wrap splices require a longer wire

length in order to complete the splice and have a

splice diameter equal to three times the diameter of the

wire used.

• Hook Splices Hook Splices require the most wire

length in order to complete the splice and have a

splice diameter equal to three times the diameter of the

wire used.

• Lap Splices Lap splices, like mesh splices, require a

minimal amount of original wire length and may be

used to perform repair of a damaged wire when:

a. Sufficient slack is available in the wire to achieve

the necessary overlap, and

b. The repaired wire will not be subjected to longitu-

dinal stress after repair.

3. WIRE SPLICING

Locating/Isolating Damage Locate the damaged

wire. If the wire is broken, determine if both sections

are available. Isolate the damaged area by using point-

to-point resistance measurements.

Note: If the wire was broken (separated) by a cutting

action, the cut ends can be spliced at the point of

breakage/separation. If the wire was broken (separated)

by a pulling action, e.g., stretching or pulling until sepa-

ration, then the wire strands on both sides of the break

will have suffered hidden mechanical damage in the

form of stretching, elongation and reduction of indi-

vidual strand diameter. In such cases, where separation

was caused by a pulling action, it is desirable to remove

(cut-out) wire which could have been damaged by

stretching and installing a longer splice than would nor-

mally be used.

4. FEASIBILITY OF REPAIR

Prior to repairing damaged wires, the following consid-

erations must be made:

• Should damaged wires be replaced in their entirety

• Should wires be repaired using solder sleeves

• If complete replacement is not feasible, determine if

one section of wire may be replaced thereby limiting

the number of splices to one

• If no section of the damaged wire can be replaced,

splice in a replacement section of wire with two

splices

5. INSULATED CONDUCTOR STRIPPING

Insulated conductors should be stripped a distance

longer than required for the solder connection. This

allows for easier forming of the conductor. The excess

conductor shall be trimmed off prior to soldering. The

following stripping methods are recommended.

a. Thermal wire strippers are to be used on insula-

tions that will melt upon application of heat. This

method is preferred because it minimizes the pos-

sibility of conductor damage.

Caution: Do not use mechanical strippers on wire

smaller than AWG-20, as the strippers may stretch the

wire.

b. Mechanical strippers are to be used on insulations

that cannot be thermally stripped. This method

does not apply to enamel insulation.

c. Chemical stripper is used on conductors that have

an enamel/varnish coating for insulation.

1) Follow the manufacturer’s instructions on the

length of time for the chemical reaction to take

place.

2) The stripper may have to be neutralized. Follow

the manufacturer’s safety precautions on both

equipment and personnel.

Warning: Chemical strippers contain ingredients

harmful to both skin and eyes. Prescribed protective

clothing, including industrial goggles/spectacles, shall

be worn when opening the container and during use. If

stripper gets on skin, wash immediately with fresh

water and soap and rinse freely. If stripper gets into

eyes, ﬂood with large quantity of fresh water. Do not

apply ointments or salve, obtain medical aid at once.

Follow manufacturer’s safety instructions.

October 2003 IPC-7711A

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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

6. TINNING

Background: Once a conductor is exposed to the envi-

ronment, oxidation begins to take place. The tinning of

a conductor is important to ensure a quality solder con-

nection. Tinning stranded wire reduces the probability

of wire damage during forming of necessary bends.

Note: Do not tin wires that will be used on the mesh

splice.

Wicking: Wicking of solder underneath the wire insu-

lation is not usually a problem, as long as the insulation

is capable of withstanding the heat and as long as the

wire does not have to remain ﬂexible at the point of the

splice. If the insulation cannot withstand the heat of

tinning/soldering, or if the wire must be bent, or remain

ﬂexible at the point of the splice, then it is recom-

mended that an anti-wicking tool be used when tinning

the wire and a thermal-shunt or heat-sink be used when

soldering the splice.

Flux: Any ﬂux used during tinning or soldering of

wire will wick up under the wire insulation. Flux which

wicks up under the insulation can not be extracted or

removed by cleaning. Therefore, only Rosin Mildly

Activated (RMA) type ﬂux should be used when

tinning/soldering stranded wire. Flux identiﬁed as Rosin

Activated (RA) must not be used for tinning/soldering

stranded wire because RA ﬂux which wicks up under

the insulation contains activators which are corrosive.

Appearance: After tinning, the surface of the tinned

stranded wire should be smooth, bright, non-porous and

individual strands should be visible. The tinned surface

of a solid wire, or a component lead should be smooth,

bright and non-porous.

7. TINNING METHODS

Tin all areas that will be soldered during the splicing

operation. Anti-wicking tools, if used, should be sized

to the diameter of the wire being tinned. Tinning of

conductors may be accomplished using either of the

following methods.

A. Soldering Irons

1) Select the proper size soldering iron tip.

2) Select a soldering iron tip large enough and a

heat setting high enough to ensure solder melt

within 2-3 seconds.

3) Ensure that the soldering iron tip and area to be

soldered are clean.

4) Form a proper heat bridge approximately one-

third the distance down from the insulation/anti-

wicking tool.

B. Solder Pots

Note: Due to the lack of mobility, solder pots are

used for tinning conductors that are not located

inside of equipment or components leads, e.g., cable

repair/manufacture, dual inline packages, and dis-

crete components.

1) Ensure wire to be tinned is properly stripped and

held by anti-wicking tool or other means of

securing wire without damage to insulation.

2) Apply ﬂux to the area of the wire to be tinned.

3) Remove dross from properly heated solder pot.

4) Insert wire into pot to depth of tin desired, hesi-

tating approximately one second to overcome

heat sinking effect. Pull away in a swift upward

motion.

5) After tinning, it must be cleaned and rinsed in

accordance with shop practices to remove con-

taminants, and inspected to ensure ﬂux residue

has been removed.

8. SOLDERING

a. Apply solder to the junction of the iron and wire,

forming a heat bridge, and allow it to soak into the

wire.

b. Move the solder and the iron up the wire toward

the insulation/anti-wicking tool, ensuring a con-

tinuous ﬂow of solder throughout the entire tinning

process.

c. When the iron and solder reach the insulation/anti-

wicking tool, hesitate momentarily and then con-

tinue to ﬂow in solder and work back down the

wire. As you bring the solder and iron off the end

of the wire, the excess solder and all the oxidation

will follow the iron off the wire.

d. Clean the wire using approved shop practices to

remove ﬂux residue. The cleaned wire should have

a bright shiny appearance.

IPC-7711A October 2003

Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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

EQUIPMENT REQUIRED

Soldering system

Soldering handpiece

Chisel tip

MATERIAL

Flux

Flux-cored solder

Insulative tubing

NOTE

Prior to fanning the wires of this type splice, position the insulation sleeving/tubing

over the wire. Ensure that the sleeving/tubing length is sufficient to extend over the

wire’s insulation, on both sides of the spliced area, a distance of three times the wire

insulation diameter. The tubing’s inside diameter should be selected to facilitate (after

shrinking) a snug, firm fit over the wire insulation.

PROCEDURE

1. Install tip.

2. Start with tip temperature of approximately 260°C and change as necessary.

3. Form the mesh splice by fanning the wire strands on both untinned wires into a

cone shape. (See Figure 1.)

4. Gently begin meshing the wires together a minimum of 1.3 cm so that the strands

interlace evenly and of equal length. (See Figure 2.)

5. Twist the wires slowly using a slight pulling motion to restore the original lay of the

wire. Do not overtwist. (See Figure 3.)

WIRE SPLICING

6. Select appropriate heating element to establish a heat bridge and minimize the

effect of solder wicking beneath insulation. Solder in accordance with paragraph

8 in 8.1. (See Figure 4.)

NOTE

Flux contained in flux-cored solders should be sufficient to clean and solder splices.

If external flux is used, the chance of solder wicking beneath the insulation of

stranded wire is increased.

7. Clean, if required, and inspect.

8. Position insulation sleeve/tubing over the spliced area, apply heat to shrink to a

snug fit over the splice and wire insulation. (See Figure 5.)

Figure 1 Strip and Fan Wire Strands

Figure 2 Mesh Wire Strands

Figure 3 Smooth Down Strands

Figure 4 Solder Connections

Figure 5 Cover with Heat-Shrinkable

Tubing

7711A

Rework of

Electronic Assemblies

Revision:

Date: 2/98

Mesh Splice

Number: 8.1.1

Product Class: N/A

Skill Level: Intermediate

Level of Conformance: Low

Material in this manual, IPC-7711 Rework of Electronic Assemblies, was voluntarily established by Technical Committees of

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 IPC.

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Provided by IHS under license with IPC

Not for Resale

No reproduction or networking permitted without license from IHS

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