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DECEMBER 2021 I DESIGN007 MAGAZINE 57 monitor, indicators). e purpose of using both symmetry and asymmetry in this situa- tion is to visually draw the attention of the user to the primary aspects of the board design and keep attention away from the secondary support items. As the user spends more time with the board and is satiated with the primary focus of the board, the secondary items come into play. ese distinct groupings of circuits off to the sides are actually sub-dominant focal points and centers of interest, exposing yet another set of artistic principles employed by PCB designers. e use of focal points and points of interest are commonly used to organize PCB designs into coherent collections of functionalities. Focal points are areas that attract the eye and centers of interest and are meant to engage the mind. 2 To avoid conflicts between our visual and mental attention, centers of interest should also be focal points, however, focal points need not be centers of attention. An example of an area that may only need to be a focus point is the part number etched or silkscreened onto the PCB. Focal points on a PCB design are commonly imple- mented by lumping components together in functional groups and using solder mask or silkscreen to create a color contrast. Centers of interest are about how you lump components together and use the solder mask/silkscreen to con- vey meaning or spark curiosity. It is important to understand that many PCBs are visually complex in nature and use of focal points should be approached in a hierar- chical manner to avoid making the PCB/PCBA visually confusing and hard to understand. ese hierar- chies are referred to as dominant (primary), sub-dominant (second- ary), and subordinate (tertiary) focal points. 3 ere should be only one dominant focal point and it is the main focus of the design. Subordinate focal points should be used for support circuitry. Subordinate focal points should be used for items such as etched/silk- screened part numbers, quality assurance markings, or circuit arraignments focused on internal support/debugging. Figure 5 shows a complex board design utilizing hierarchical focal points. e most important physical and electrical connections take place in this 7.5" x 5" area of the board and it needs to reliably interface with nearly 400 pogo pins applying an aggre- gate force of just under 200 pounds. Figure 4: The primary focus of the board (voltage and current MUX) is the two vertically stacked patterns of relays spaced horizontally apart from each other on an offset vertical axis.