Design007 Magazine

Design007-Feb2022

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FEBRUARY 2022 I DESIGN007 MAGAZINE 53 sumer electronics differ greatly from those implemented for medical equipment, automo- tive, or aerospace and defense ap p licat ions. For e xamp le, low-volume assemblies may only require functional testing while higher-volume assem- blies or those products requir- ing uncompromised opera- tion, will most likely adapt a more sophisticated test strat- egy. Electrical Test Strategy When developing a test strategy, many factors must be considered to determine which test methods will be used. If possible, a test engineering specialist will review the schematic diagram before the cir- cuit board design begins. For example, they may suggest that the designer divides complex logic into smaller, functional logic sections; provides additional capacitor elements that enable decoupling semiconductor devices; and furnish pull-up resistors on unused logic terminals. e goal is to maximize the fault coverage, but not always at any cost. Low volume or less complex circuit board assemblies may rely on a basic functional, "go or no-go" testing while high-volume assem- bly or products having greater complexity will most likely adapt some form of automated or semi-automated functional partitioning or in- circuit testing (ICT). ese methods, when used together, could achieve 100% fault cov- erage, ensuring that no circuit board assembly leaves the factory with a potentially compro- mising manufacturing defect or functional fault. Most solder process-related defects (opens and shorts) can be detected visually using magnification. High-volume manufacturing may employ an automated optical inspection (AOI) system or even X-ray inspection sys- tems, especially suited for detecting elusive solder defects, under BGA or QFN devices, for example. Functional Test for PCB Assembly To physically secure the assembly for func- tional and partitioned circuit test applications, a dedicated fixture is developed. Electrical test will be performed with power applied to evaluate the actual performance of the finished board assembly. Access for this type of testing is typically made through an interface connec- tor or probe interface with input/output lands dedicated to the test procedure (Figure 1). With fewer component parts to contend with, the detection of component failures or assembly related defects will be fairly routine. When the assembly fails due to component malfunction, identified components will be de-soldered and replaced before secondary inspection and re-testing. Larger boards with high component density will require more complex test preparations. Partition testing is commonly semi-automated, requiring a dedicated test station and access to benchtop measurement gear. is type of test- ing is oen utilized for measuring amplifier, RF and IF (intermediate frequency), and other sensitive circuit functions. e partitioning of functions allows the operator to isolate and make specific measurements on critical circuit Figure 1: Functional circuit test access using I/O connector.

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