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Toxics Use Reduction Institute · Surface Solutions Laboratory
 
Toxics Use Reduction Institute




Surface Solutions Laboratory

Trial Report



Trial Number 0

(Client Number 155, Project Number 2)

Trial Purpose: To identify contaminants on rejected parts.

Date Run: 08/29/01

Experiment Procedure:
Background on FT-IR Spectrometry: Fourier Transform Infrared spectroscopy correlates vibrational energy to a compound's molecular signature. Similar to other high-tech methods such as GC (gas chromatography), the curves generated in this analytical technique are both quantitative for species identification (the placement of the curve on the electromagnetic spectrum) and qualitative for amounts (the area under the curve). A relatively expensive instrument, a FT-IR spectrometer requires special training and care in sample preparation. Not all contaminants can be analyzed this way and interpretation of graphs can be difficult due to the presence of interfering peaks. It may be used in cleanrooms or disk drive manufacture where the origins of contamination may be entirely unknown and the amounts of contamination very low.

Initially, a background was run on the FT-IR, followed by a IPA blank. Working with the supplied rejected parts, several IR cards were made up by wiping the parts with a IPA soaked swab. The IPA was used to dissolve and transfer any materials on the surface to the IR cards. After wiping the parts, the “dirty” swab was used to coat the IR card window. Each card made up was then analyzed in the instrument. The generated spectra were then compared with several other cards that were made up with possible sources of contamination. These included toluene, wax and a combination of the two.

Trial Results
The following table details the source of the sample, the observations made and which spectrum was generated by the sample.  Figure 1 shows all of the
samples and the possible contaminants analyzed.  Samples 1 and 2 taken from the same source closely matched the Toluene spectrum.  A third sample, #8,
from source A revealed a close match to the Wax & Toluene mix.  Sample 3 was slightly different than Samples 1 and 2, with a round peak at the
beginning of the line.  This peak was in the same area as wax and toluene, but with some other interference that may be IPA.  Sample 4 closely matches
the wax and toluene mix.  Samples 5 and 6 from  source C had similar characteristics as wax spectrum and the IPA spectrum.  Sample 7 was another that
followed the wax and toluene curves.
 
Table 1.  FT-IR Analysis Observations.
?Sample  Source           Observations-Comparison           Line Color
1                A                Toluene                                       light purple upper
2                A                Toluene                                       black
3                B                Toluene & IPA & maybe Wax      yellow
4                B                Wax & Toluene                            light blue
5                C                Wax & IPA                                  dark purple
6                C                Wax & IPA                                  thin dark green
7                D                Wax & Toluene                           dark blue
8                A                Wax & Toluene                           medium blue
Toluene                                                                           medium blue upper
Wax                                                                                light green
Wax & Toluene                                                               light purple
Isopropyl Alcohol                                                             thick dark green
Background                                                                      red

Substrates         Ceramics; Gold Plated
Contaminants:   Unknown; 
Possible Contamination Sample #          Sources
Toluene                         1, 2, 3, 4, 7, 8   3 of 4
Wax                               3, 4, 5, 6, 7, 8   4 of 4
IPA                                 3, 5, 6               2 of 4


Success Rating
A cleanliness study, addressing only various analytical techniques.

Conclusion
It appears that several of the supplied contaminated parts did have some of the wax remaining on them after the toluene cleaning. In addition most of the parts had toluene residue as well. The FT-IR readings made by SCL should not be considered as a final determination as to the identification of the source of contamination.