Which tools are best for SMT rework—conduction or convection?
The Award Winning
Dage XD7600NT
100
HP
The Ultimate in X-ray Inspection
Figure 7. Print pattern printed in only the center.
0.05 mm, or 2 mil, so that all flux residue
left on the PCB will be trapped. Therefore,
cleaning flux residue from under the land
array is very important.
A jig has been designed to print paste
onto center pad patterns only. Then the
part can be picked up with a convection
rework system that has both vacuum pick
up and prism vision alignment.
Placement is controlled by the process
of machine, but placement height is set
with a tool that is part of the jig. Basically,
n Unique Dage NT100 sealed-transmissive X-ray
the print pattern is 0.1 mm (4 mils) thick,
printed only in the center of the package
tube providing feature recognition down to
(Figure 7). The center is then printed with
100nm (0.1 microns)
solder paste. When the solder paste reflows
n Unique 10 watts power at sub-micron
it fills the gap between the package and the
PCB top surface, which is only 0.5 mm (2
feature recognition
mils).
n 2.0 Mpixel images with >65,000 greyscale levels
If the part is crushed down onto the
all displayed on a 24” HD monitor
paste too hard, it will bridge and cause
solder shorts under the part when reflowed.
n CT Option
A spacer that is the same size and thickness
as the printed stencil is supplied with the
See what the XD7600NT
100
HP can do you for at:
tool set. Once the height is set correctly Productronica 2009: Stand A2:361
by placing the spacer onto the PCB, the
actual part is printed with solder, aligned
email:
dpi-sales@dage-group.com
to the pad and reflowed to the PCB using a
www.dage-group.com
convection rework system.
This reflows and secures the part to the
PCB by soldering center pad array only.
After the reflow of the inner array, the
outer leads of the QFP are soldered by hand
using a drag solder method or pin-by-pin
necessary to go to 245°-250°C to remove an incorrect profile, usually due to too
method.
DG-2811 XD7600NT Colour Ad.v2.indd 1
the part. fast a reflow time.
20/8/09 11:56:55
conclusion
• Conduction removal is faster than • There should be no browning of
•
convection but may damage the parts solder resist on the top side of a PCB
A good rework process should first
during removal. from hot air, which caused by high
consider if the parts are to be reused or
• Consider adjacent components such nozzle temperatures required when no
discarded, then select the appropriate
as electrolytic capacitors that may preheater or weak preheat temperatures
tools.
•
get damaged from heating, or plastic are used from below.
The process of removal can be faster
connectors that will deform from too • Rework should be considered as a value
than placement with hot air tools.
much heat. added process. Rework saves the PCB,
There is no need to go to peak
• Voids should not be seen in reflowed reduces the cost to replace a defective
temperatures for removal. Lead free
solder paste joints under T0220, LGA device and reinforces a manufacturer’s
solder melts at 217ºC, so safe removal
or Fusion pack devices. This indicates commitment to quality.
can be done at 225°C. It is not
www.globalsmt.net Global SMT & Packaging – October 2009 – 19
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