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December 2014 • The PCB Design Magazine 35 Paul reid's career in PCB fabrica- tion and reliability testing spans 35 years. one of his specialties is producing technical anima- tions of failure modes induced by thermal excursions, giving him insight into the mechanisms of circuit board failure. reid is now retired. To contact the author, click here. In conclusion, the use of HDI PWB reli- ability in lead-free applications is a dual- edged sword. The copper interconnections are more prone to a breakdown and the ma- terial is more prone to damage. That is not to say that robust PWBs cannot be made, but there is a challenge in producing them. One must test the interconnect and the material in order to confirm robustness in a given ap- plication. PCBDESIGN Figure 11: Cohesive crack. Figure 10: adhesive delamination. Figure 12: Crazing with a CaF failure. feature HDI PWB RELIABILITY continues