Solder flux technology

Bono, D., The Assessment of the Corrosivity of Soldering Flux Residues Using Printed Copper Circuit Board Tracks, Solder Surface Mount Technology, No. 2, June 1989, pp. 22-29. 

M.S. Heutmaker, LM. Fletcher, and J.E. Sohn, Measurement of Stray Capacitance Due to Solder Flux Residue at Radio Frequency Circuit Boards, IEEE MTT-S Symposium, Technologies for Wireless Applications, Feb 20-22, 1995... 

The next critical component for this material was the development of the flux and activator system for the paste. This proved to be a key factor in the success of this project. As the wettability of lead-free alloys is lower than eutectic Sn-Pb, a suitable flux system was critical to the successful introduction of the MD s conversion to lead-free. In addition to the flux system having the properties to promote wetting, the requirements for screen printing, stencil life, tackiness, and so on were also important when evaluating a solder paste system. Flux technology is discussed in... 

The entire process technology was expected to meet all European environmental and product recycling legislation at the end of the twentieth century. This specifically applies to metals that replace the lead (Pb) content of solder alloys and all the other materials, products, and waste generated by the manufacturing processes or in any potential recycling routes. Results of the project in terms of the improved solders, fluxes, and processes should be applicable in European industry immediately following the end of the project [15-25]. A key element to this objective is... 

Dispensing. In surface-mount technology, three classes of materials must be dispensed on to the circuit board adhesives, fluxes, and solder pastes. Each of these three categories, which utilize very similar equipment options for the actual dispensing action, is discussed in the following subsections. 

The impact of Pb-free technology on wave soldering has largely occurred in the equipment performance. It has been determined that the same solder bath temperatures that are used for Sn-Pb processes (250 to 270°C) are suitable for the Sn-Ag-XCu Pb-free alloys. Therefore, excessive dross formation and flux residue removal have not become a significant problem during equipment operation. The lack of shiny fillets with the Sn-Ag-XCu alloys has been addressed by modified alloys having Ni and Ge additions that alter the solidification process, which leads to shinier fillet surfaces. 

It is beyond the scope of this chapter to provide a detailed explanation of SPC. Rather, there will be a qualitative discussion of process control that addresses those factors affecting circuit board assembly, beginning with defect types in electronic solder joints. Then the discussion will turn to process control as it pertains to the basic assembly steps (e.g., dispensing, pick-and-place, etc.). The various material sets (e.g., circuit board, solder paste, flux, etc.) will be incorporated in the discussion. Also, the use of Pb-free soldering technology will be addressed where applicable. 

Difficulty of Inspection. No-clean residues, especially from surface-mount technology (SMT) soldering, are generally hard, transparent polymerized deposits that interfere to some degree with solder-joint inspection. The deposit can crack and sometimes operators will mistake the cracked flux residue deposit for solder-joint cracking. The residue is also reflective, which can interfere with visual inspection or automatic optical inspection (AOI) methods. 

McKay, C. A., The Role of Activators in Fluxes for Microelectronics Soldering, Microelectronics and Computer Technology Corporation Technical Report P-11-405-91,1991. 

Pickering, K., Southworth, C.,Wort, Parsons, A., and Pedder, D. J., Hydrogen Plasmas for Flux Free Flip-Chip Solder Bonding, Journal of Vacuum Science and Technology, Vol. A, No. 8(3), May-June 1990, pp. 1503-1508. 

Heat is the most important parameter with lead-free solder materials. The challenge is to develop flux systems that provide greater thermal stability, whereby the heat exposure dwell time is more important than absolute temperature levels. Despite the fact that our industry has to switch to lead-free technology, increasing demands for higher quality of final electronics... 

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