Apply Low Residue Flux to all the leads on the SMD you're removing
With a soldering iron, melt the low temperature alloy
Surface Mount Technology
A method of assembling printed wiring
boards or hybrid circuits, where
components are attached to pads on the
board surface, as distinct from through-hole
technology, where component leads are
inserted into holes.
There are 3 major types of Surface Mount Assemblies:
(Full SMT board with parts on one or both sides of the
(Surface mount chip components are located on the
secondary side of the Printed Board (PB). Active SMCs
and DIPs are then found on the primary side)
(They use passive chip SMCs on the secondary side, but
on the primary side only DIPs are used)
It depends on a number of factors
• Market needs
• Package moisture sensitivity
• Thermal and solder joints reliability
• As the packaging density increases, thermal problems are
compounded, with a potential adverse impact on overall
Feed mechanism used to load components
into a pick-and-place machine
SMD pick-and-place machine (with
simulated motion blurs)
Soldering is a process
in which two or more
metal items are joined
together by melting
and flowing a filler
metal into the joint, the
filler metal having a
relatively low melting
CONVENTIONAL HOT GAS SOLDERING
•No compressed air
nozzles (low costs)
•Fast reaction of infrared
•Central areas will be heated more
than peripheral areas
•Temperature can hardly be
controlled, peaks cannot be ruled out
•Covering of the neighboured
components is necessary to prevent
damage, which requires additional
time for every board
•Surface temperature depends on the
characteristics: dark surfaces will be
heated more than lighter surfaces
During hot gas soldering, the energy for heating up the
solder joint will be transmitted by a gaseous medium. This can be
air or inert gas (nitrogen)
•Simulating reflow oven
•Switching between hot gas and
nitrogen (economic use)
•Standard and component-
specific nozzles allow high
reliability and reduced process
•Allow reproducible soldering
•Thermal capacity of the heat
generator results in slow reaction
whereby thermal profiles can be
•A rework process usually
undergoes some type of error, either
human or machine-generated, and
includes the following steps:
1. Melt solder and component
2. Residual solder removal
3. Printing of solder paste on PCB,
direct component printing or
4. Placement and reflow of new
•A specially formulated alloy in wire form is
designed to melt at the low temperature of around
136 degrees F, 58 degrees C. It eliminates the
potential for damage to the circuit, adjacent
components, and the device itself.
•Liquid flux and a soldering iron are used to melt
this low temperature alloy that is specially
formulated to stay molten long enough to react with
existing solder. The SMT device can then be easily
removed with a vacuum pen
Apply Low Residue Flux to all the leads
on the SMD you're removing
With a soldering iron, melt the low
Easily lift device off the board with a
•Finally, the boards are visually inspected for
missing or misaligned components and solder
•If needed, they are sent to a rework station where
a human operator corrects any errors.
• They are then sent to the testing stations to
verify that they operate correctly.
Thoroughly clean site and solder new
device to PBC
•Smaller components. Smallest is currently 0.4 x 0.2 mm.
•Much higher number of components and many more connections per
•Fewer holes need to be drilled through abrasive boards.
Simpler automated assembly.
•Small errors in component placement are corrected automatically (the surface
tension of the molten solder pulls the component into alignment with the solder
•Components can be placed on both sides of the circuit board.
•Lower resistance and inductance at the connection (leading to better
performance for high frequency parts).
•Better mechanical performance under shake and vibration conditions.
•SMT parts generally cost less than through-hole parts.
•The manufacturing processes for SMT are much more
sophisticated than through-hole boards, raising the
initial cost and time of setting up for production.
•Manual prototype assembly or component-level repair
is more difficult given the very small sizes of many
•SMDs can't be used with breadboards , requiring a
custom PCB for every prototype. The PCB costs dozens
to hundreds of dollars to fabricate and must be
designed with specialized software.
•SMDs' solder connections may be damaged by potting
compounds going through thermal cycling.