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50 DESIGN007 MAGAZINE I AUGUST 2024 PCBs on Layers In the early days, PCBs had one or two con- necting layers, which required only a single dielectric sheet with a conducting layer on one or both sides. As a child, electronics fas- cinated me, and as soon as I could read, I turned to hobby magazines. Some described the new technology: Instead of discrete wires, they could draw connections of electronic cir- cuits on copper-clad dielectric, and then etch away the copper where the connection wasn't needed. Later, I made little gadgets with transistors that I had purchased from a local hobby shop that sold materials, tools, and components for radio amateurs and hobbyists. With the non- market economy in those days, a transistor cost about the same as six pounds of bread. I built small portable radios on homemade printed circuits. e first attempts failed mis- erably. e hand-drawn pattern of ink that had to be baked before etching oen peeled off too early. Once I discovered the correct tempera- ture, length of baking over the kitchen gas range flame, and the proper etching time, the boards became more reliable. An example is shown in Figure 2. It is the audio amplifier of a battery- powered portable radio I built in the late '60s 4 . By the late 1990s, glass-reinforced epoxy had replaced Paper Bakelite, and etching and plating had become carefully optimized and automated processes. e circuit complexity required several routing layers, plated through- holes, and blind and buried vias (which had recently become available). Instead of manu- ally drawing the pattern with ink, engineers used CAD soware to perform the routing. e CPU module in Figure 3 (reproduced from Slide 12 5 ) had a 20" x 8.5" 24-layer PCB. e board did not have blind or buried vias and used only standard low-cost FR-4 laminates, but it had selective gold plating. e price of the prototype bare boards in small quantities was around $600. As production ramped up, prices came down. In the 2000s, the cost of bare PCBs with standard laminate materials, no blind or buried Figure 2: Homemade printed circuit board from the late 1960s. Figure 2a shows the top view of the single- layer PCB with the components. Figure 2b is the back side of the board with the copper traces. There was no need for vertical connections or plated through-holes, so the cost of the driver was simply the cost of the laminate. The color of the bare dielectric reveals this was an early Paper Bakelite board laminate. I recall the cost was probably around the price of a couple of scoops of ice cream at the time. a b Figure 3: CPU module of SUN Microsystems V880/V890.