Laser soldering of small pitch BGAs on Plexiglas substrate PCBs
The paper presents the results of the study and the procedure of soldering 200µm pitch BGAs on circuits on PMMA (Poly-methyl-methacrylate or Plexiglas) substrate, starting from the paste deposition process, fine placement of the BGAs and finally soldering. The novelty in this research is that it had to face two restrictions. The combination of PMMA substrate, transparent to laser, and SnBi, ecologic solder paste, which required a low and very well-controlled soldering temperature, and the small size of the BGAs which needed a punctual soldering. These particularities led the team to use laser for soldering, due to the possibility of highly accurate energy calculation and very small size of the focused beam.
Laser soldering control using optical imaging
Purpose – The use of lasers to selectively solder joints in electronic assemblies has a number of advantages over methods which involve heating of the whole assembly. However, the localised energy delivery means that the heating and melting behaviour of the solder is particularly dependent on external and process influences. This paper aims to propose a new approach to monitoring and feedback control of the melting process through image acquisition and processing.Design/methodology/approach – In order to evaluate the proposed feedback strategy, a series of experiments have been performed using a semiconductor diode laser controlled by a PC, which also performs image acquisition and processing operations. Two main processing techniques, based on edge detection and Fourier analysis, have been evaluated.Findings – It has been shown that the proposed technique is capable of controlling laser pulse duration to correct for variations in joint geometry, material parameters and laser energy delivery and results i...
The finite element modelling of laser soldering for electronic assemblies
The laser provides a controllable means of supplying localized energy for solder joint formation and is a valuable tool in electronics manufacture. The modelling of heating behaviour in typical structures requires consideration of many different phenomena and the resulting models can become complex. The work described here shows that, given appropriate modelling assumptions, finite element models are able to give accurate predictions of heating in high‐pin count devices as well as a valuable insight into the important factors affecting the success of laser soldering operations. In particular, it is shown here that conduction through the body of the component being soldered does not significantly affect heating of the solder but that variations in copper track thickness can result in a doubling of the required soldering time. In addition, it is shown that conduction through the printed circuit board is important when using a scanned laser beam to solder multiple joints. Copyright © 2002 John Wiley & Sons, Ltd.