Can lead-free and lead-containing PCBs be cleaned in a single process? Can lead-free and lead-containing PCBs be cleaned in a single process?
Figure 3. Results of experiment one, with 50 mg/l of lead salt, conducted at room Figure 4. Results of experiment two, with 100 mg/l of lead salt, conducted at
temperature. room temperature.
Figure 5. Results of experiment three, with 50 mg/l of lead salt, conducted at Figure 6. Results of experiment four, with 50 mg/l of lead salt, conducted at
approximately 50˚C. approximately 65˚C.
This worst-case scenario (65°C) the cleaning solution. The analysis of the the results of the study only apply for cus-
was included to further demon- cleaner then showed a lead content of 6.3 tomers using the above-mentioned cleaners,
strate that no detectable cross mg/l. as a direct correlation to the observed data
contamination was noticeable. Subsequently, lead-free test boards were is only possible in such cases.
cleaned with this ‘used’ cleaning agent at In contrast, traditional surfactant-based
Overall it was observed that the lead
varying temperatures. Afterwards, the lead products with higher alkaline pH-values
content of the assemblies in all four experi-
content on the boards was measured by show a tendency to dissolve more lead.
ments never exceeded 0.3 mg/cm
2
.
XRF analysis. This increases the risk of cross-contami-
simulation of a mixed
The results show that no significant nating lead-free assemblies. In this case,
cleaning process
increase in lead on the lead-free boards was the compliance with RoHS requirements
observed. All measured values are compa-
With this laboratory test result in hand,
is questioned if both, lead containing and
rable with the readings of the reference
final trials were performed to examine the
lead-free assemblies are cleaned in one
values prior to cleaning.
machine-specific rinsing capabilities.
single process.
This is an important result as it shows
These experiments were conducted
that the amount of dissolved lead is rela- conclusions
in standard spray-in-air inline cleaning
tively small within the applied agents. This This study had the aim of collecting data
equipment. Analog to the first experi-
applies even in worst-case scenarios with on lead contamination of lead-free as-
ments, ‘contaminated’ media were used at
high cleaning temperatures and extended semblies that were cleaned together with
a working concentration of 15%. Prior to
contact times (Table 1, sample 6). leaded assemblies. The analysis of customer
lead-free substrates, 500 lead-containing
The solubility of lead is dependent on samples provided an average lead level be-
assemblies were cleaned in the inline equip-
the type of cleaning agent used. Therefore, low the critical limit, despite the different
ment to establish the base values for lead in
30 – Global SMT & Packaging – November 2008
www.globalsmt.net
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