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Which tools are best for SMT rework—conduction or convection?
Which tools are best for
SMT rework—conduction or
Paul Wood, OK International, Garden Grove, CA, USA
issue with electrolytic capacitors or plastic
Different devices demand
Over the course of the paper, the following
connectors. While there should be no
different processes and safety;
components are used to illustrate the use
mechanical damage removing a large pitch
however, temperature of the
and effects of convection and conduction
SOIC, as shown in Figure 1, if the part is
component and reliability are
tools for rework applications:
removed with a higher temperature tunnel
often not included in the tool 1. SOICs
tip because no preheater is used from
selection method. Often an
2. PLCCs
the bottom, the part could be thermally
operator is given very basic
3. T0220 power transistor with
damaged. If reuse is to be considered, a
tools and asked to repair many
ground pads
preheater should be used. This will allow for
different devices with one tool.
4. Small fine pitch connectors
much lower temperatures of tunnel tips and
This can lead to dangerous
5. Fusion pack from Amkor, a new
could save the part from thermal shock and
technology LGA and QFP in one
practices and quality is often
compromised. Method 3: Hot air
This paper will show five
reworking sOic and very fine sOic
Convection is the preferred removal
examples of rework using
method when the component is mounted
conduction and convection Removal
incorrectly or if parts are to be reused.
repair and discuss the Method 1: Thermal tweezers
If the PCB is small or low mass, then
advantages and disadvantages
SOIC-style parts can be reworked using
the part can generally be reworked using a
of both methods.
thermal tweezers to remove all dual inline
convection tool. If the part is on a thicker or
SMT components. This is a very quick,
higher mass substrate, then top and bottom
efficient removal method.
convection preheating should be used for
Tweezers can bend the fine pitch leads,
removal and placement.
Keywords: Rework, SOIC, though, so this method is not recommended

PLCC, Power Transistors, Fine
if the parts are expected to be reused.
Replacing SOICs
Pitch Connectors, FusionPack
Method 2: Tunnel soldering tip
SOICs, which have pitches of 1.27 mm and
As an alternative to tweezers, a tunnel
0.8 mm, can be placed by hand and easily
tip can be used. These are made for the
hand soldered back.
specific size and shape of the SOIC then
They can also be replaced with a dot of
tinned up with solder to help hold the part
paste per pad or a small line of paste run
to tip with surface tension.
along the pads at 90º and then reflowed
When solder is molten, lift and use
with hot air. If bridges occur, these can be
a wiping action
with the tip to
raise the part off
the PCB surface.
Finish with a small
rotation or sliding
action (Figure 1).
One advantage
of the tunnel tip
is that the heating
is localized,
so there is no
adjacent heating
Figures 1a & b. SOIC removal.
14 – Global SMT & Packaging – October 2009
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