All photoimageable solder resists include photo initiators in their formulation, serving the purpose of initiating the radicalic polymerisation under UV light exposure. The most common photo initiators 907 and 369 used worldwide were reclassified in January 2020 by ECHA, the European Chemical Agency. They are now part of the SVHC Candidate List (Substances of Very High Concern).
The polymerisation process triggered during the exposure of the solder resist is not fully completed. As a consequence, one would find condensate material with such photo initiators in drying and cur-ing ovens. In some cases, they crystallise in the form of white powder or needles, while in others, they would accumulate in condensate traps.
Recently, Peters has analysed how much photoinitiator is actually discharged from the solder resist. You will find the results and an evaluation on whether PCBs are subject to labelling in accordance with the REACH Regulation 1907/2006 due to the photoinitiator contained, in the recently published White paper “A Challenge in PCB Production: SVHC Classified Photoinitiator Type 907”.
Peters has developed alternative products at an early stage, for which ample practical experience has been gained in the meantime. A manufacturer who, due to the current SVHC issue, is faced with a change-over to a new solder resist, will find powerful state-of-the-art systems without the photoinitiators 369 and 907 when choosing Elpemer® products of the editions 733 (for contact exposure) or 766 (for direct exposure with LED or laser-based light sources).
Photo 1: Needles consisting of photoinitiator 907 in a pre-drying oven for solder resists
Photo 2: Condensate material from a condensate trap of a reflow oven at an EMS company’s site – 7.7 % of weight of this brownish, semi-liquid material was identified as photoinitiator 907 by GC-MS-analysis
