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Intrusive reflow with SNIC paste
Figure 4. Sample boards being processed by Peter Figure 5. X-ray images produced on a DAGE system.
Barton at ACW manufacturing facility in Wales
through his ASSCON vapour phase system.
The profile was conducted on a six-
layer, 1.6,mm thick board, the same design
as was used in the production trials.
Figure 3 shows the reflow profile
achieved on three thermocouples placed
across the length of the connector and
processed through the ASSCON vapour
phase reflow system, running a 240˚C
fluid
The reason for using a 240˚C fluid
as opposed to the more common 230˚C
Figure 6. Microsection on connector pins.
fluid is the reflow temperature of the
tin/copper/nickel alloy. SAC alloys are
selective show little practical difference.
217-221˚C where as tin/copper/nickel
The example shows the copper barrel/
reflows at 227˚C. Some engineers like to
solder joint removed from the board.
use the same alloy type in reflow, wave and
Harting Connectors have co-operated
selective soldering.
in the past with National Physical
The x-ray images in Figure 5 show
Laboratory (NPL) Teddington, London
100% fill on connector pins with six-layer,
during the introduction of lead-free
1.6 mm boards. On the left are convection
soldering which allows customers to
with HASL and the right vapour phase
compare the results from production
with silver finish. The x-ray images show
and from long term reliability testing.
virtually no void formation and solder
NPL has been running DTI projects in
fillets on the top and bottom of the
collaboration with industry to evaluate
through hole barrel with positive solder
Figure 7. Through-hole pin after pull testing.
the solder joint reliability of various lead-
fillets.
free solders for many years. The original
In the microsections on connector pins
PIHR reliability project consisted of 145 exception of vapour phase reflow. Many
after intrusive reflow with tin/copper/
boards with mixtures of lead-free alloys— thanks to Peter Barton of ACW for giving
nickel paste shown in Figure 6, the left is
SnAgCu, SnAgBiCu, SnCu, SnPbAg—and your columnist time on his system, which
an OSP board and the right is a gold over
a standard tin/lead control. The test is running a 240˚C fluid. Also to DKL
nickel board finish. The microsections
board consisted of a wide selection of Metals for the sample of SN100C solder
were taken so measurements could be
surface mount components as well as paste for the production trials.
taken on the copper plating thickness after
the connector, which was reflowed. The
soldering to examine the difference in
samples went through thermal cycle testing Bob Willis is a process engineer working in
copper dissolution between SAC and tin/
of 2200 cycles of -55˚C +125˚C with dwell the electronics industry, providing training,
copper/nickel alloys.
times of 40 minutes with no electrical consultancy and process/product failure
The solder joint strength and long
failure. analysis. Bob also offers on site workshops
term reliability of PIHR are no different
The results speak for themselves: the on conventional and lead-free manufacture,
than with conventional wave or manual
PIHR process is not that difficult; you Bob will be running three new “Package On
soldering operations. The joints also easily
just need a good 10-point plan in place Package” PoP workshops in the UK to support
meet the visual requirements for national
from the design stages to final inspection. the release of a new interactive CD-ROM and
and international standards like IPC 610D.
The peak temperatures for lead-free are inspection wall charts. Workshops take place at
Figure 7 shows typical example of a
satisfactory and lower than some of the AXIOM, Wales and ITRI, St Albans details at
through hole pin after pull testing from
profiles we see featured in the industry. www.bobwillis.co.uk. Bob is happy to assist you
an intrusive reflow production board.
Although the reflow temperature of tin/ set up and optimise production lines for users
Comparing solder joint pull strength
copper/nickel is higher than SAC, the and also provides conferences and workshops
between samples produced by wave and
peak temperature can be the same with the worldwide.
www.globalsmt.net Global SMT & Packaging – October 2009 – 53
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