IPC-CM-770D-1996 - 第166页

IPC-CM-770 Januaty 1996 IPC-I- Figure 30-7 Small Hot Air Jet Lap Solder Joint Component Removal IPC-I- Figure 30-8 Lap Reflow Soldering Tool Used for Component Removal IPC-I- Figure 30-9 Hot Gripper - Hand Force Componen…

January

1996

IPC-CM-770

'igure

30-3

Commercially Available Surface Mount

Component

R&R

System

the printed board structure to melt the solder joints, fol-

lowed by manual lift

off

of the component after the sol-

der has melted. Heat guns with a simple fixture mount-

ing (see Figure 30-4 and 30-5) were first used for the

removal of surface-mount components. Later, commer-

cial systems (see Figure 30-6) provide much the same

function but with better air flow controlled by nozzles,

and better control of the printed board structure assem-

bly with board positioning holders.

CAUTION: The hot air is not highly concentrated nor

selectively applied and can cause undesirable overheat-

ing of the components conductive patterns. The printed

board substrate itself can be readily damaged since con-

trol of manual lift

off

depends on human judgment and

sensitivity.

Hot Air Jet

Heat is transferred from a hot gas pencil

or a solder extractor by reversing the flow of air through

the tool to locally heat and desolder individual leaded

lap solder joints on components. Caution must be exer-

cised to insure that all residual solder has been removed

from the solder extractor (see Figure 30-7).

3. Lap Reflow Desoldering

A lap reflow soldering tool

can locally melt the solder in individual short leaded lap

solder joints (see Figure 30-8).

4. Thermal TweezerdHot Gripper

Heat is transferred

from the formed solder joints along the perimeter of the

leadless and short-leaded device. The operator grips the

component to be removed with the hot gripper tool by

hand force, then after the operator senses the solder

joints are molten the hot gripper tool is used to lift

off

Figure

30-4

Single-sided Hot Air Component Remover

IPC-I-

Figure

30-5

Double-sided Hot Component Remover

IPC-I-

Figure

30-6

Commercial Hot Air Component Remover

the component from the printed board surface (see

figures 30-9 and 30-10).

CAUTION: Due to human sensitivity limitation, uncon-

trolled clamping and shearing forces can be applied prior to

solder melt, all resulting in damage to the substrate conduc-

tive pattern.

6-29

Licensed by Information Handling Services

IPC-CM-770

Januaty

1996

IPC-I-

Figure 30-7 Small Hot Air Jet Lap Solder Joint

Component Removal

IPC-I-

Figure 30-8 Lap Reflow Soldering Tool Used for

Component Removal

IPC-I-

Figure 30-9 Hot Gripper

Hand Force Component

Remover

CAUTION: This method provides some improvement over

the Hot Gripper since it utilizes more sensitive finger tip

gripping, but still depends upon the sensitivity of the indi-

vidual. Like the hot gripper, the thermal tweezers are nor-

mally used to remove chip resistors and capacitors (or

other small two terminal components), and should be lim-

ited to removing multileaded components having less than

twenty leads.

30.6.5 Through-Hole and Surface Mounted Component

Removal

The following are the general methods for the

Figure 30-10 Thermal Tweezer -Finger Tip Controlled

Component Remover

removal of components or solder from solder joints on/in

printed board structures. These methods include component

removal and/or replacement of through board (standard

components, dual-inline packs, and pin-grid arrays) and

surface mounted devices.

30.6.5.1 Wicking Method

The wicking method incorpo-

rates either stranded copper wire or a braid saturated with

flux, which is then applied between the solder to be

removed and a hot soldering iron.

CAUTION: The wicking method is only recommended for

surface solder joints and is not recommended for use on

plated through hole solder joints.

30.6.5.2 Impulse Solder Sucker Method

The impulse

solder sucker method employs a single pulse vacuum gen-

erating device utilizing a squeeze bulb or a spring operated

plunger mechanism with a Teflon orifice through which the

vacuum is applied to the solder to remove it from the joint.

CAUTION: This method will not consistently remove sol-

der from plated through holes and frequently the compo-

nent lead will resweat to the plated through hole wall.

30.6.5.3 Soldering Iron SolderlSolder Method

The sol-

dering irodsolder sucker combination method is a hollow

tipped soldering iron combined with an impulse solder

sucker mechanism.

CAUTION: This method will not consistently remove sol-

der from plated through-holes and frequently the compo-

nent lead will resweat to the plated through hole wall.

30.6.5.4 Heat-and-Pull Method

The heat-and-pull meth-

ods essentially involve heating the solder joint(s) by one of

several different methods and pulling the component

lead(s) out of the solder connection.

CAUTION: The heat-and-pull methods must be used with

caution on surface mount components and are generally not

recommended for the component removal of multileaded

components with through board solder joints.

6-30

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January

1996

IPC-CM-770

30.6.5.5 Combination Methods

These solder extraction

methods provide controlled combinations of heat, pressure,

vacuum, and airflow for the controlled removal of any sol-

der joint configuration. Advantages: This solder removal

method is easily manipulated, fully controllable and allows

a trained and skilled operator to easily remove solder and

components from most types of assemblies.

A. Solder Extraction (Continuous Vacuum) This method

uses a hollow soldering iron and tip to melt the solder and

after the solder is molten, the solder is sucked out of the

solder joint by an operator controlled vacuum pump. This

method can also be used for clinched leads, blindhlocked

holes, and auxiliary heating.

Solder Extraction (Pressure Mode) This method uses a

hollow soldering iron and tip to melt the solder and after

the solder is molten, to blow it out of the solder joint by an

operator controlled vacuudpressure pump. This solder

extractor pressure method is suitable for removing solder

from blind or blocked component lead mounting holes.

30.6.5.6 Clip-and-Fix Method

In the clip-and-fix

method, the component leads of the component to be

removed are cut

off

at (or near) the component body. This

is generally not performed when the component to remove

is thought to be good. In some cases it may be desirable to

remove individual component leads with a small jet of hot

air. After solder melt the component lead is lifted

off

the

land.

30.6.6 Replacement of Surface Mounted Devices

The

general requirements and procedures for surface mounted

components are in IPC-A-610.

Prior to replacement, the surface mount component and the

land patterns on the printed board structure may have to be

hot air leveled, or pretinned and fluxed. The component

must then be precisely positioned on the land pattern and

stabilized (held in place) during solder reflow and cool

down.

CAUTION: Hot air leveling can cause undesirable over-

heating of the component, adjacent components, solder

joints, and the printed board structure.

It is not recommended, but hand soldering replacement

with a microscope aid can be successful.

6-3

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