Circuits Assembly - July 2008 - (Page 59)

Conformal Coatings min., covering a range of approximately -25° to +125°C. 1 Thermal shock tests are slightly different, however. A shock test is harsher than a cycling test. Consisting of two separate chambers, one at the lowest temperature and one at the highest temperature required, the test board is passed through from one chamber to the next. This results in an immediate change to the surrounding temperature of the board. The flexibility, appearance and SIR are evaluated following a set number of cycles through either the gradual or shock method. The novel coating was tested in high humidity and 5% salt environments at room temperature and at 40°C for 21 days, in accordance with IEC 60068-2-78 and IEC 60068-2-11, respectively. SIR was measured immediately after testing and again after 15 min. recovery, to identify coating performance. The results (Figure 1) showed the performance of the novel coating in such environments is comparable to solvent-based coatings. In some cases the coating exhibited superior performance with faster recovery times (Figure 2). In thermal shock tests, the test was set to 15 min. at -70° and +130°C, and 20 complete cycles were performed in accordance with IEC 61086-2 section 4.2. (It should be noted thermal shock tests were carried out at a wider range than specified in IEC 61086-2: 70°C instead of -55°C.) Long-term temperature extreme tests – thermal aging – were also performed for 500 hr. at -60° and +125°C, in accordance with IEC 61086-2 section 4.3. Flexibility and adhesion testing was carried out in accordance with ISO 1519 and BS EN ISO 2409, respectively. The novel coating showed no reduction in SIR, adhesion or flexibility in either test. Finally, the coating was Figure 3. The novel coating exposed to an environmen- exhibits excellent edge definital cycling test per MIL- tion on flat and populated 46058C. This consisted of 24 surfaces, permitting accurate hr. immersed in water, 24 hr. selective coating. at 105°C, 96 hr. at 95-100% humidity and a final 8 hr. at -70°C. The appearance and SIR were evaluated following the cycle and again remained unchanged (>1 x 10 13 Ω). Other conformal coating performance testing includes electrical properties evaluation. This is essential to all applications of conformal coatings to a PCB, regardless circuitsassembly.com Elreha Ad -half.indd 1 Circuits Assembly JULY 2008 6/9/08 9:38:28 AM 59 http://www.jetpcb.com http://circuitsassembly.com

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Circuits Assembly - July 2008 Contents Caveat Lector Industry News Market Watch Talking Heads Focus on Business Global Sourcing On the Forefront Screen Printing Tech Tips Will Electronics Follow the Sun? ‘Warm’ Manufacturing Heats Up Reputation Trumps Recession, China ‘Web Circuits’ A Novel Non-VOC Conformal Coating Krypton: Benchmarking Customer Satisfaction 2008-09 CIRCUITS ASSEMBLY Buyers Guide Wave Soldering Pb-Free Lessons Learned Process Doctor Materials World SMTA Int'l Product Preview Ad Index Assembly Insider Technical Abstracts

Circuits Assembly - July 2008

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