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46 The PCB Magazine • July 2014 Introduction Substrates have become more critical with regard to pitch and density in today's designs with challenges for passive components in terms of surface placement. This negates the opportunity for high speed, high cost compo- nents to be placed on the surfaces of the PCB. With this the capacitance and resistive com- ponents have to be embedded into the design. This has been accomplished with the advent of buried capacitance cores and buried resis- tors. Unfortunately, this has caused some chal- lenges to the ET test centers/labs in the ability to effectively test these buried passive compo- nents. Processes have had to change and adapt to these new technologies. The paper will dis- cuss what these new technologies are and how the electrical test arena has adapted to provide accurate testing of the buried resistors and ac- commodate the buried capacitive cores to not receive false errors from the grid testers and fly- ing probes. Resistors In the past, pull-up, terminating and volt- age dividing resistors have been placed on the surface of the PCB. Early applications were stan- dard carbon resistors placed on the board utiliz- ing plated through-holes. As can be seen in Figure 1, the standard car- bon resistor took up a lot of space on the PCB. You will also notice in the photo that capacitors are also stealing valuable space from the surface topography. As time progressed, SMT technol- ogy was introduced and the older, bulky stan- dard carbon resistor was replaced by the newer SMT packages (Figure 2). by Todd L. Kolmodin, Manfred Ludwig, Howard Carpenter and Rick Meraw gardien SerViceS uSa and china F e a t u r e Electrical Testing of Passive Components

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