Multiple Solder Limits: UL-Standard Generated

Estimated reading time: 1 minute

A breakthrough in the reassessment of soldering parameters could be achieved at the initiative of the long-time proxy holder of Peters, Rüdiger Dietrich. The industry associations of the German electronics industry made a common certification recommendation and a new standard was generated.
The U.S. certification institution UL (Underwriter Laboratories) followed the recommendation of the ZVEI (Zentralverband Elektrotechnik und Elektronikindustrie  German Electrical and Electronic Manufacturers' Association) and the FED (Fachverband für Design, Leiterplatten und Elektronikfertigung  Professional Association for Design, Circuit Board and Electronics Manufacturing). 

"The solution which has been developed at the roundtable of both associations is practice-oriented and constructive," Rüdiger Dietrich says.
The recommendation for solder parameters will be published in the next edition of UL 796. The roundtable, which was initiated by former Peters technical director Dietrich could obtain already back in 2019 a freezing in of the existing UL certifications. UL themselves had started the discussion of the reassessment of the real multiple solder processes instead of single solder parameters.
"Thanks to the successful cooperation of the two associations we had a decisive influence on the creation of new specifications for multiple solder limits. The industrial sector worldwide will take profit from the German initiative through the establishment within the UL international set of standards," says Dietrich, who is retired but still active within the associations.
For a future solution the more than 30 participants from the fields of base materials, solders, lacquers, pcbs and assemblies, evaluated a great number of solder profiles from existing lead-free and non-lead-free solder processes. Additionally the companies involved produced various samples which were exposed to several reflow cycles.
Most of the solder profiles are covered by the specifications of the two well-known norms IPC-TM-650 method 2.6.27A and J-STD-020. The decisive factor for the thermal stress is not the individual peak temperatures and solder time but the entire heat quantity brought into the pcbs. This can be given in Ks (Kelvin seconds) and corresponds to the area under the curve of a solder profile (see picture).
The proposal submitted to UL by FED/ZVEI to realise the "Multiple Solder Limits" comprises a solder profile (consisting of  both IPC-TM-650 and J-STD-020) which counts on this surface solution and thus makes a certain flexibility of solder parameters in practical life possible.