Optimizing batch cleaning for removing lead-free flux residues on PCAs
test boards
flux residue removed
Batch Test 1 processed the boards using a
under the chip caps.
wash time of 15 minutes (five minutes to
LFHR3 cleaning feel
come up to 150°F wash temperature and 10
off at the higher wash
minutes at 150°F wash temperature). The
temperature but the
mean value of the LFHR pastes cleaned un-
other two LFHR solder
der 1210 chip caps ranged from 45-58% flux
pastes improved. The
residue removed under the chip caps. The
data findings sup-
LFSR pastes cleaned under 1210 chip caps
port the first research
ranged from 78-100% flux residue removed
hypothesis that soft
under the chip caps. For the 1825 chip caps,
residues are possible to
cleaning under the LFHR ranged from 54-
clean under the Z-axis
68% and cleaning under the LFSR 64-77%
in a batch dishwasher
flux residue removed under the chip caps.
machine and that clean-
!
The data findings indicate that a higher
ing typically improves
level of soft flux residue was removed under
with higher processing
the Z-axis, which is consistent with the first
temperatures. The data
research hypothesis. The data indicates that
findings also indicate
longer wash time is needed to clean under
that flux residues do
the Z-axis in the batch dishwasher design
not clean at the same
due to the lower dynamic cleaning rate.
rate and some materials
Batch Test 2 processed the boards using
must be matched to
a wash time of 40 minutes (five minutes to
cleaning material and
come up to 150°F wash temperature and
temperature effects.
35 minutes at 150°F wash temperature).
Batch Test 5
For the 1210 chip caps, cleaning under the
processed the boards at
LFHR ranged from 44-58% and clean-
a concentration of 9%
ing under the LFSR 66-77% flux residue
using a wash time of 40
!
removed under the chip caps. For the 1825
minutes (10 minutes
chip caps, cleaning under the LFHR ranged
to come up to 200°F
from 54-68% and cleaning under the LFSR
wash temperature and
66-77% flux residue removed under the
30 minutes at 200°F
chip caps. The data findings indicate that
wash temperature). The
no improvement over Batch Test 1 from an
strategic thinking for
additional 25 minutes wash time. This find-
reducing the wash con-
ing rejects the second research hypothesis
centration was to test
that infers higher wash time improves the
the surface tension ef-
static and process cleaning rate.
fects, which improve at
Batch Test 3 processed the boards using
lower wash concentra-
a wash time of 25 minutes (five minutes to
tion. For the 1210 chip
come up to 175°F wash temperature and
caps, cleaning under
20 minutes at 175°F wash temperature).
the LFHR ranged from
!
For the 1210 chip caps, cleaning under the
66-100% and cleaning
Figures 5a, 5b & 5c. Data findings from the spray-in-air control test
LFHR ranged from 45-80% and cleaning
under the LFSR 100%
under the LFSR 100% flux residue removed
flux residue removed dissolution properties of the wash chem-
under the chip caps. For the 1825 chip caps,
under the chip caps. For the 1825 chip caps, istry. The question among the research
cleaning under the LFHR ranged from 61-
cleaning under the LFHR ranged from 46- team was what would happen if the wash
75% and cleaning under the LFSR 80-93%
79% and cleaning under the LFSR 88-99% concentration were dropped to 5%. For the
flux residue removed under the chip caps.
flux residue removed under the chip caps. 1210 chip caps, cleaning under the LFHR
The data findings indicate cleaning im-
LFHR3 cleaning was consistent with Batch ranged from 62-84% and cleaning under
provement from higher wash temperature,
Test 4 with cleaning falling off at the higher the LFSR 96-100% flux residue removed
which supports the third research hypothe-
wash temperature. Lowering the wash chem- under the chip caps. For the 1825 chip caps,
sis that the cleaning rate doubles every 18°F
istry concentration indicates the importance cleaning under the LFHR ranged from 47-
increase rise in wash temperature.
of wash temperature but also indicates the 76% and cleaning under the LFSR 69-96%
Batch Test 4 processed the boards using
value of matching the cleaning material to flux residue removed under the chip caps.
a wash time of 40 minutes (10 minutes to
the soil matrix. Decreasing the wash concentration from
come up to 200°F wash temperature and
Batch Test 6 processed the boards at 9% to 5% slightly tailed off cleaning, which
30 minutes at 200°F wash temperature).
a concentration of 5% using a wash time indicates optimal concentration range for
For the 1210 chip caps, cleaning under the
of 40 minutes (10 minutes to come up to the soil matrix.
LFHR ranged from 40-98% and cleaning
200°F wash temperature and 30 minutes Batch Test 7 first placed the test
under the LFSR 100% flux residue removed
at 200°F wash temperature). The benefi- boards into a controlled atmosphere oven
under the chip caps. For the 1825 chip caps,
cial results obtained from dropping the at 200°F oven using a wash time of 40
cleaning under the LFHR ranged from 46-
concentration from 18% to 9% indicated minutes (10 minutes to come up to 200°F
84% and cleaning under the LFSR 96-99%
the importance of wash temperature and wash temperature and 30 minutes at 200°F
www.globalsmt.net Global SMT & Packaging – September 2008 – 15
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