Realistic solderability testing with lead-free solders

Microelectronics International

ISSN: 1356-5362

Article publication date: 1 August 2004




(2004), "Realistic solderability testing with lead-free solders", Microelectronics International, Vol. 21 No. 2.



Emerald Group Publishing Limited

Copyright © 2004, Emerald Group Publishing Limited

Realistic solderability testing with lead-free solders

Realistic solderability testing with lead-free solders

Keywords: Lead-free soldering, NPL

Some recent work has given wider application to a conventional and trusted test. Historically, solderability testing has been based on using rosin fluxes, but in modern assembly technologies the levels of rosin have decreased remarkably. The resultant call for a more new realistic test using fluxes currently employed in the industry (e.g. no-clean) has at present been successfully answered.

New NPL work has explored the use of two new test fluxes based on weak organic acids, one solvent-based and the other water-based (i.e. VOC-free). Encouragingly, the work demonstrates, that when formulated with an acid number 40-45, both flux systems:

  • show maximum solderability for fresh components;

  • can discriminate fresh and aged components;

  • represent fluxes used in today's industry; and

  • can clean the solder globule at elevated lead- free soldering temperatures.

Crucially, therefore, these two new fluxes can be used with the existing test equipment and procedures in tests, which relate closely to current industry assembly practice. They can be used for testing both conventional lead-containing and new lead-free solders, with both Sn-Pb and Sn finishes.

Another key finding was that solderability is dependent not just on flux activity, but also on flux chemistry and interaction of the flux with the finished material. The new test is therefore ideal for discriminating between the performances of components with different finishes. Indeed, Pd, Sn-Pb and Sn finishes displayed very different wetting characteristics.

The beneficial impact of nitrogen inerting with Sn-Ag-Cu lead-free solder, especially in opening the narrow process window, was reconfirmed in this work.

For more information, contact: Alan Brewin. Tel: 020 8943 6805; Fax: 020 8614 0428; E-mail:

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