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SMT007-Aug2019

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12 SMT007 MAGAZINE I AUGUST 2019 in electronics by shorting the circuit, it is cru- cial that the coating material covers all metal surfaces at an appropriate thickness to provide these barrier properties. To understand coating coverage with regards to potential tin-whisker mitigation, the IPC TR-57 "Conformal Coatings: The State of the Industry" white paper investi- gates hundreds of boards coated with a variety of common coating chemistries and applica- tion methods, which were meticulously cross- sectioned for thickness. The results were sur- prising with numerous areas of extremely low coverage being found along with wide ranges of thickness on different component types. A typical result for a gull-wing device, such as a QFP lead, is shown in Figure 2. The 2K series of coatings is significantly dif- ferent in its protective capabilities due to its capacity for greater coating thickness and enhanced edge coverage. 2K coatings are VOC- free, fast-curing, high-performance, two-part conformal coatings that provide a solvent-free alternative to both UV and silicone materials, require less capital investment than UV mate- rials, and improve on the performance of most silicones in harsh environments. The major- ity of coatings in the 2K range are hydropho- bic, giving excellent protection against water immersion, salt mist, and humidity, making them ideally suited for automotive electronics. Why Was the 2K Range Developed? The main reasons why Electrolube decided to develop a new breed of two-part (2K) con- formal coating systems simply results from the increasing expectations for conformal coatings to perform effectively in higher temperature extremes and withstand more thermal shock cycles and to address the coverage concerns addressed by the white paper. Many conven- tional materials are becoming obsolete because they are failing to meet new maximum operat- ing temperatures or provide insufficient cover- age required for successful condensation tests, which are needed by global automotive manu- facturers. Electrolube also wanted to dispel any myth that applying a coating material more thickly achieves better coverage. Overapplying a coating only increases the amount of stress on the coating and the assembly, which can lead to disaster during thermal shock testing, especially with UV-curable materials, which crack and then provide no protection at all. Addressing these challenges was the driving force behind the development of the 2K range. Electrolube's 2K coatings have been designed to withstand high-temperature extremes and have the application ease of a coating with the performance properties of an encapsula- tion resin. 2K coatings can be applied more thickly without placing unnecessary stress on the assembly or the coating, which eliminates any concerns about cracking. 2K coatings also accomplish the coverage requirements for suc- cessful resistance against condensation, tin- whisker mitigation, and reinforcing dielectric functions. The 2K range is solvent-free, low- odour, and low-hazard, which enables users to reduce their VOC emissions and improve the safety of their process. Why Would You Use a 2K Coating Rather Than a Single-coating System? It is time to consider using a 2K confor- mal coating when a traditional coating fails to deliver the necessary protection for the end-use environment. 2K coating can provide consider- ably increased protection across the board for resistance against condensation, high humid- ity, immersion, and corrosion. The additional Figure 2: Typical cross-section showing difficulty achieving coverage (blue layer) with traditional coating materials.

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