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58 PCB007 MAGAZINE I JULY 2018 Feature by Sven Kramer LACKWERKE PETERS GMBH & CO. KG KEMPEN, GERMANY Abstract This article focuses on three different coat- ing material groups that were formulated to operate under high thermal stress and are ap- plied at the printed circuit board manufactur- ing level. While used for principally different applications, these coatings have in common that they can be key to a successful thermal management concept especially in e-mobility and lighting applications. The coatings looked at consist of: Specialty (green transparent) liquid photo- imageable solder masks (LPiSM) are compat- ible with long-term thermal storage/stress in excess of 150°C. Combined with the appropri- ate high-temperature base material, and along with a suitable copper pre-treatment, these sol- der resists are capable of fulfilling higher ther- mal demands placed on them. In this context, long-term storage tests as well as temperature cycling tests were carried out. Moreover, the effect of various copper pre-treatment methods on the adhesion of the solder masks was exam- ined at 150, 175 and 200°C over the aging pro- cess. For this purpose, test panels were stored for 2000 hours at the respective temperatures and were submitted to a cross-cut test every 500 hours. Within this test set-up it was found that a multi-level chemical pre-treatment gives significantly better adhesion results, in partic- ular at 175°C and 200°C, as compared to a pre- treatment by brush or pumice brush. Break- down voltage as well as tracking resistance were also studied. For an application in LED technology, the light reflectivity and white colour stability of the printed circuit board are of major im- portance, especially when high-power LED are used which can generate larger amounts of heat. For this reason, a very high coverage power and an intense white colour with high reflectivity values are essential for white solder masks. These "ultra-white" and largely non- yellowing LPiSM need to be able to withstand