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November 2014 • The PCB Magazine 59 todd Kolmodin is the vice president of quality for Gardien services usa, and an expert in electrical test and reliability issues. to read past columns, or to contact Kolmodin, click here. WHAT IS 4-WIRE KELvIN? continues Z-Axis (3-Dimensional Adjacency) In conjunction with horizontal adjacency, this methodology can be used. This will scan the horizontal (line of sight) with the addition of the Z-axis (3 rd axis.) This method requires up- front information of the entire stack-up of the PCB. This is critical as an over measurement in the Z adjacency will have the flying probe per- form isolation testing well above and beyond what is required resulting in excessive test time. Figure 2 outlines Z-axis. From Here How the OEMs wish their product validated will always be their decision. Currently, the bed of nails is still available but the cost outweighs the benefits of the flying probe. Cost of tool- ing is greatly reduced, speed of program repair is virtually painless and the quality of the PCB test is strong. PCB References 1. Images copyright by IPC and IPC-9252A. Images appear with permission from IPC. figure 2: vertical layer adjacency. (source: iPC) 1. Grounded plane: C-l2. 2. dotted area denotes vertical layer adjacency area for net f on layer l3. 3. nets to be included in the vertical layer adjacency list for net f: b-l2, C-l2, d-l2/l3, G-l3/l4, h-l4, i-l4.