Abstract

Laser removal of surface oxides and small particles from copper surfaces was carried out using a Q-switched Nd:YAG laser. Oxide layers and small particles on copper surfaces should be removed for the improvement of solder quality on printed circuit boards (PCBs) and for the prevention of circuit failure or loss of production yield during the fabrication of microelectronic devices. A selective removal of surface oxides from a copper surface was achieved by the laser treatment, which was confirmed by on-line acoustic monitoring of the process. An angular laser cleaning technique in which the laser irradiates the surface at a glancing angle was used for effective removal of the particles from the surface. The unique characteristics of this technique and the cleaning mechanism are discussed.

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References

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  1. G. Vereecke, E. Rohr, M. M. Heyns, "Laser-assisted removal of particles on silicon wafers," J. Appl. Phys. 85, 3837-3843 (1999).
    [CrossRef]
  2. Y. F. Lu, W. D. Sung, M. H. Hong et al, "Laser removal of particles from magnetic head sliders," J. Appl. Phys. 80, 499-504 (1996).
    [CrossRef]
  3. K. Coupland, P. R. Herman, B. Gu, "Laser cleaning of ablation debris from CO2-laser-etched vias in polyimide," Appl. Surf. Sci. 127-129, 731-737 (1998).
    [CrossRef]
  4. K. Mann, B. Wolff-Rottke, F. Muller, "Cleaning of optical surfaces by excimer laser radiation," Appl. Surf. Sci. 96-98, 463-468 (1996).
    [CrossRef]
  5. Anonymous, "Photonic cleaning process moves to heavy industry," Photonics Spectra, pp. 22 (Mar. 1997).
  6. G. Schweizer, "CO2 laser reduce waste from aircraft paint removal," Opto & Laser Europe, Issue 18, pp. 42-43 (Mar. 1995).
  7. J. M. Lee, In-process and intelligent monitoring systems for laser cleaning process (PhD thesis, University of Liverpool, 1999), Chp. 1.
  8. J. M. Lee, K. G. Watkins, "Laser cleaning for electronic device fabrication," The Industrial Laser User, Issue 18, pp. 29-30 (Feb. 2000).
  9. J. M. Lee, K. G. Watkins, "Real-time surface monitoring in the laser cleaning of copper for soldering processes," Lasers in Eng. 8 (3), 229-239 (1999).
  10. A. Kearns, C. Fischer, K. G. Watkins et al, "Laser removal of oxides from a copper substrate using Q-switched Nd:YAG radiation at 1064 nm, 532 nm and 266 nm," Appl. Surf. Sci. 127-129, 773-780 (1998).
    [CrossRef]
  11. R. DeJule, "Trends in wafer cleaning," Semiconductor International, pp. 64-68 (Aug. 1998).
  12. R. A. Bowling, "A theoretical review of particle adhesion" in Particles on Surfaces, K. L. Mittal, ed. (Plenum, New York, 1988), Vol. 1, pp. 129-142.
    [CrossRef]
  13. A. C. Tam, W. P. Leung, W. Zapka et al, "Laser-cleaning techniques for removal of surface particulates," J. Appl. Phys. 71 (7), 3515-3523 (1992).
    [CrossRef]
  14. Y. F. Lu, W. D. Sung, B. W. Ang et al, "A theoretical model for laser removal of particles from solid surfaces," Appl. Phys. A 65, 9-13 (1997).
    [CrossRef]
  15. D. W. Lynch, W. R. Hunter, "Optical constants of metals" in Handbook of optical constants of solids, E. D. Palik, ed. (Academic Press, 1985).
  16. E. A. Brandes, G. B. Brook, ed., Smithells Metals Reference Book (Butterworth-Heinemann, 1992), Chp. 14.

Other (16)

G. Vereecke, E. Rohr, M. M. Heyns, "Laser-assisted removal of particles on silicon wafers," J. Appl. Phys. 85, 3837-3843 (1999).
[CrossRef]

Y. F. Lu, W. D. Sung, M. H. Hong et al, "Laser removal of particles from magnetic head sliders," J. Appl. Phys. 80, 499-504 (1996).
[CrossRef]

K. Coupland, P. R. Herman, B. Gu, "Laser cleaning of ablation debris from CO2-laser-etched vias in polyimide," Appl. Surf. Sci. 127-129, 731-737 (1998).
[CrossRef]

K. Mann, B. Wolff-Rottke, F. Muller, "Cleaning of optical surfaces by excimer laser radiation," Appl. Surf. Sci. 96-98, 463-468 (1996).
[CrossRef]

Anonymous, "Photonic cleaning process moves to heavy industry," Photonics Spectra, pp. 22 (Mar. 1997).

G. Schweizer, "CO2 laser reduce waste from aircraft paint removal," Opto & Laser Europe, Issue 18, pp. 42-43 (Mar. 1995).

J. M. Lee, In-process and intelligent monitoring systems for laser cleaning process (PhD thesis, University of Liverpool, 1999), Chp. 1.

J. M. Lee, K. G. Watkins, "Laser cleaning for electronic device fabrication," The Industrial Laser User, Issue 18, pp. 29-30 (Feb. 2000).

J. M. Lee, K. G. Watkins, "Real-time surface monitoring in the laser cleaning of copper for soldering processes," Lasers in Eng. 8 (3), 229-239 (1999).

A. Kearns, C. Fischer, K. G. Watkins et al, "Laser removal of oxides from a copper substrate using Q-switched Nd:YAG radiation at 1064 nm, 532 nm and 266 nm," Appl. Surf. Sci. 127-129, 773-780 (1998).
[CrossRef]

R. DeJule, "Trends in wafer cleaning," Semiconductor International, pp. 64-68 (Aug. 1998).

R. A. Bowling, "A theoretical review of particle adhesion" in Particles on Surfaces, K. L. Mittal, ed. (Plenum, New York, 1988), Vol. 1, pp. 129-142.
[CrossRef]

A. C. Tam, W. P. Leung, W. Zapka et al, "Laser-cleaning techniques for removal of surface particulates," J. Appl. Phys. 71 (7), 3515-3523 (1992).
[CrossRef]

Y. F. Lu, W. D. Sung, B. W. Ang et al, "A theoretical model for laser removal of particles from solid surfaces," Appl. Phys. A 65, 9-13 (1997).
[CrossRef]

D. W. Lynch, W. R. Hunter, "Optical constants of metals" in Handbook of optical constants of solids, E. D. Palik, ed. (Academic Press, 1985).

E. A. Brandes, G. B. Brook, ed., Smithells Metals Reference Book (Butterworth-Heinemann, 1992), Chp. 14.

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Figures (10)

Fig. 1.
Fig. 1.

Soldering features before and after cleaning the surface

Fig. 2.
Fig. 2.

Laser craters on an oxidised copper surface with the sequence of the number of laser pulses with 3.5 J/cm2 at 1064 nm

Fig. 3.
Fig. 3.

Acoustic waves emitted from an oxidised copper substrate under laser irradiation from the 1st to 4th pulse respectively

Fig. 4.
Fig. 4.

Acoustic emission intensity as a function of the number of laser pulses from an oxidised copper surface and a clean (non-oxidised) copper surface

Fig. 5.
Fig. 5.

Laser cleaning efficiency as a function of the laser fluence

Fig. 6.
Fig. 6.

Copper surface morphology after 10 laser pulses at 1.0 J/cm2

Fig. 7.
Fig. 7.

Illustration of angular laser cleaning

Fig. 8.
Fig. 8.

Copper surfaces after 10 laser pulses at 0.14 J for (a) the glancing angle of 10° and (b) the perpendicular angle of 90°

Fig. 9.
Fig. 9.

Laser cleaning efficiency as a function of the laser fluence at the glancing angle of incidence

Fig. 10.
Fig. 10.

Illustration of the laser absorption on the surfaces of the particle and the substrate for different laser incident angles (The density of “dots”indicates the amount of heating due to the laser absorption on the surfaces)

Equations (4)

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F a = h r 8 π Z 2 + h r a 2 8 π Z 3
Δ l = α δ Δ T
a = Δ l t p 2
F = m a

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