The IEEE Boston Reliability Chapter cordially invites you to attend a joint meeting and plant tour
with SMTA Boston Chapter and iMAPs organizations on Nov. 1st, 2017:
Laser Exfoliation Removal of Conformal Coatings From CCA PCB Pad Surfaces and Design for Rinsability
Wednesday evening, November 1st, 2017, Raytheon, Andover, MA
Circuit Cards Assemblies-CCAs are manufactured to meet Class 3 military-grade requirements –they must work the first time, every time. Certain electronic components from recent production builds were detected with cleaning residue remaining, and it appears that the component housing design is a major factor that determines whether a component entrains & entraps residues. To ensure protection to moisture or extreme environments, the CCA undergoes a conformal coating process on CCA exposed surfaces. Prior to conformal coat, the surface of the CCA is semi aqueous chemically cleanedto provide a surface condition suitable for the coating to properly adhere. However, If the cleaning solutions get entrained / entrapped within the components, residual contamination may cause materials degradation of the components, which may limit the electrical performance of the device. As a result, a study was initiated to understand the susceptibility of entrainment / entrapment of cleaning residues on 28 different components, each with various component cover / attachment constructions and vent open areas.
CCAs-circuit card assemblies for military applications require a high level of performance and reliability, and typically undergo a CC-conformal coating process after SMT-surface mount technology assembly to protect the circuit card and attached electrical components from exposure to moisture and harsh environments. However, certain areas of the CCA or PCB-printed circuit board metallized surfaces are desired to be free of conformal coating and are required to be clean, solderable and electrically / thermally conductive. Current conformal coating de-masking processes are time consuming and labor intensive. A more cost effective and automated laser-aided exfoliation method was evaluated and successfully demonstrated to remove parylene C conformal coatings from ENIG-plated Cu pads. The parylene was removed within a precise pad area, and tested to be solderable to enable subsequent wire-soldering and consistent sealant coverage in a cost-effective manner. This paper will discuss the “physics” of laser ablation, laser exfoliation, materials interactions, test and characterization methods used to evaluate and validate the laser-aided removal processes on actual production CCA product.