'THERE IS NO INSTANT PUDDING' - UNDERSTANDING THE ROLES TEST PLAYS IN MANAGING THE QUALITY OF ELECTRONIC PRINTED CIRCUIT BOARD ASSEMBLIES

摘要

The primary role of all Printed Circuit Board Assembly (PCBA) manufacturers is to produce defect free products; however all PCBA manufacturers, whether they like to admit or not, produce defects. Typical modern Surface Mount Technology (SMT) lines produce 300 to 500 defects for every million PCB assembly operations. Not all defects, however, result in faults that cause the PCBA to malfunction in its target environment. The goal of manufacturers is to find the defects on their PCB assemblies; categorize the defects; repair those faults that cause assemblies to malfunction; and correct the manufacturing processes that allowed the defects to occur. Improving manufacturing quality levels to accomplish those objectives requires a hierarchical test strategy and a complementary selection of test and inspection equipment -so that repair actions are focused on true faults and process improvements are focused on reducing marginal defects that lead to faults. The strategy strikes a balance between the short term pressures to ship product and the long term goals of achieving world class manufacturing quality levels. The topics covered by this paper include the different types of fault classes that may be present on a PCB and the type of test and inspection equipment that is best suited to detect them; a review of industry studies related to manufacturing defect levels; definitions of different PCBA defect categories and associated defect spectrum; the hierarchical test levels involved in improving manufacturing quality; standardized methods to measure and report test fault coverage; and the manufacturing complications caused by false failures.