PCB007 Magazine

PCB007-June2021

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62 PCB007 MAGAZINE I JUNE 2021 Volts, amperes, and ohms: in electrical test, these terms are very familiar. Combinations of these electrical elements make up the standard electrical test of the average PCB. Standard electrical test uses the IPC specification 9252 as a baseline. Depending on the performance class, different parameters are used to screen the board. ere are many machines out there that can perform these basic tests, and this has been the way of life for decades. However, life changes. ese design guys and gals do not stop the train of evolution. Packag- es become smaller, PCBs become smaller, and newer electrical characteristics come in to play. Now we must deal with farads and Mr. Hen- ry—aer Joseph Henry. See what I did there? Today, new requirements bring buried ca- pacitance and inductance. Although today's flying probe machines are familiar with ca- pacitance via the indirect test and capacitive discharge analysis, direct measurement of the actual values become more challenging. If the design drawing is provided and locations for direct capacitive measurements are given (with values), the machines of today can pro- vide this test much akin to buried resistance. However, inductance becomes more of a challenge. Most fixture testers are ill-equipped to test anything other than the standard ET parameters using volts, amps, and ohms. Mr. Henry introduces a variable that these me- tering systems simply cannot measure. Bur- ied or active inductance is not anything new to PCBs but the ability to properly measure the inductance is. In the past, simple primary and secondary passive coils are laid out in a PCB resembling nested circles or blocks. Resis- tance of the primary and secondary circuits can easily be measured but if there is a short in either the primary or secondary circuits to itself (remembering the circular patterns) the change of resistance in the primary or second- Meet Mr. Henry and Don't Blow a Fuse Testing Todd by Todd Kolmodin, GARDIEN SERVICES USA Figure 1: Circular coil. Figure 2: Square coil.

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