The Flexible Permanence Of Copper Tape Circuits
Generally speaking, [Hales] prefers plywood as the substrate to paper or cardboard for durability. He starts by drawing out the circuit and planning where all the tape traces will go and how wide they need to be. Then he lays out copper traces and pads, rubs the tape against the substrate to make it adhere strongly, and reinforces joints and laps with solder before adding the components. As you can see, copper tape circuits can get pretty complicated if you use Kapton tape as insulation between stacked layers of traces.
The Flexible Permanence Of Copper Tape Circuits
Dude, you gave me a nice idea.Re/create a flat cable with stripes of copper cable and (transparent) duct tape.The whole assembly does not need to have the right pitch, only the ends to connect existing things if needed.
In various other experiments I have also used aluminium tape (aluminium foil + double-sided adheseive). It feels almost identical to the copper stuff. I suspect that in this format it is too structurally weak to cut skin, just as normal kitchen foil is.
PCBs can be single-sided (one copper layer), double-sided (two copper layers on both sides of one substrate layer), or multi-layer (outer and inner layers of copper, alternating with layers of substrate). Multi-layer PCBs allow for much higher component density, because circuit traces on the inner layers would otherwise take up surface space between components. The rise in popularity of multilayer PCBs with more than two, and especially with more than four, copper planes was concurrent with the adoption of surface mount technology. However, multilayer PCBs make repair, analysis, and field modification of circuits much more difficult and usually impractical.
Each trace consists of a flat, narrow part of the copper foil that remains after etching. Its resistance, determined by its width, thickness, and length, must be sufficiently low for the current the conductor will carry. Power and ground traces may need to be wider than signal traces. In a multi-layer board one entire layer may be mostly solid copper to act as a ground plane for shielding and power return. For microwave circuits, transmission lines can be laid out in a planar form such as stripline or microstrip with carefully controlled dimensions to assure a consistent impedance. In radio-frequency and fast switching circuits the inductance and capacitance of the printed circuit board conductors become significant circuit elements, usually undesired; conversely, they can be used as a deliberate part of the circuit design, as in distributed-element filters, antennae, and fuses, obviating the need for additional discrete components. High density interconnects (HDI) PCBs have tracks and/or vias with a width or diameter of under 152 micrometers. 
Initially PCBs were designed manually by creating a photomask on a clear mylar sheet, usually at two or four times the true size. Starting from the schematic diagram the component pin pads were laid out on the mylar and then traces were routed to connect the pads. Rub-on dry transfers of common component footprints increased efficiency. Traces were made with self-adhesive tape. Pre-printed non-reproducing grids on the mylar assisted in layout. The finished photomask was photolithographically reproduced onto a photoresist coating on the blank copper-clad boards.
The first step is to replicate the pattern in the fabricator's CAM system on a protective mask on the copper foil PCB layers. Subsequent etching removes the unwanted copper unprotected by the mask. (Alternatively, a conductive ink can be ink-jetted on a blank (non-conductive) board. This technique is also used in the manufacture of hybrid circuits.)
Subtractive methods remove copper from an entirely copper-coated board to leave only the desired copper pattern. The simplest method, used for small-scale production and often by hobbyists, is immersion etching, in which the board is submerged in etching solution such as ferric chloride. Compared with methods used for mass production, the etching time is long. Heat and agitation can be applied to the bath to speed the etching rate. In bubble etching, air is passed through the etchant bath to agitate the solution and speed up etching. Splash etching uses a motor-driven paddle to splash boards with etchant; the process has become commercially obsolete since it is not as fast as spray etching. In spray etching, the etchant solution is distributed over the boards by nozzles, and recirculated by pumps. Adjustment of the nozzle pattern, flow rate, temperature, and etchant composition gives predictable control of etching rates and high production rates. As more copper is consumed from the boards, the etchant becomes saturated and less effective; different etchants have different capacities for copper, with some as high as 150 grams of copper per litre of solution. In commercial use, etchants can be regenerated to restore their activity, and the dissolved copper recovered and sold. Small-scale etching requires attention to disposal of used etchant, which is corrosive and toxic due to its metal content. The etchant removes copper on all surfaces not protected by the resist. "Undercut" occurs when etchant attacks the thin edge of copper under the resist; this can reduce conductor widths and cause open-circuits. Careful control of etch time is required to prevent undercut. Where metallic plating is used as a resist, it can "overhang" which can cause short-circuits between adjacent traces when closely spaced. Overhang can be removed by wire-brushing the board after etching.
Laminates provide the backbone for increasingly complex circuits built on both rigid and flexible (flex) substrates. They provide mechanical integrity to flex circuits while allowing designers the freedom to fit circuits into the available footprint. All the materials in multilayer flex laminates must be chosen to combine mechanical flexibility with sufficient electrical performance.
The laminate market is evolving to support the needs of high-speed, high-frequency circuits that connect 5G networks and power the next generation of consumer electronics. Flexible laminates are used in smartphone antennas and configurations that require thin substrates with tight bending radii. Such applications need thin, flexible designs made from low-loss materials to ensure signal integrity.
Current trends for developing miniaturized electronic devices place emphasis on achieving performance levels generally associated with integrated circuits. Here, we demonstrate an on-chip micro-supercapacitor that can be integrated with MEMS devices and CMOS in a single chip using the LightScribe direct writing technique. The structure of the device is schematically illustrated in Fig. 5b, with an ionogel used as the electrolyte. The device was fabricated using the same process described earlier, except for the plastic substrate that has been replaced with an oxidized silicon wafer, Fig. 5c. Figure 5d shows that the device reveals superior electrochemical performance with ultrahigh power, comparable to that demonstrated on the flexible substrate. This technique may thus present a low-cost and scalable solution for on-chip self-powered systems.
Conductive thread is a fiber that conducts electricity. Because it is thin and flexible, like ordinary thread, conductive thread traces can take many shapes and connect to a variety of conductive materials and components. Conductive thread is particularly useful for creating sewn circuits (also known as soft circuits or e-textiles) in applications that combine circuitry and textiles with the use of a needle.
Although conductive thread is most commonly used to make wearable electronics, it may also be paired with paper and conductive tapes. While it is most commonly used for attaching sewable LEDs, sensors, microcontrollers, and battery holders into garments, it is also useful for creating interactive components such as switches and sensors (such as a tilt sensor) that partner well with paper circuits.
Another advantage of multilayer flex circuits is that they are more flexible than traditional flex circuits. This is because they can accommodate more than one conductor layer. The rigid portions of the circuit act as support for its components, while the flexible sections provide interconnectivity. Multilayer flex circuits were used in military applications and have gained wide commercial acceptance. However, they have made substantial gains in the commercial world in recent years.
The rolled copper foil used in flexible printed circuits has an excellent flex fatigue property, adequate half-softening temperature, and good tensile strength. Its thickness ranges from five to fifty microns, and its softening temperature is 120-150deg C. Therefore, the copper foil rolled for flexible circuits is suitable for most electrical and electronic applications. However, the annealing process is ideal for applications where the copper foil flex circuit is not prone to damage or deterioration.
The primary conductive element in flexible laminates is a metal foil. Copper foil is the most popular metal foil choice, primarily because of its low surface oxygen content and excellent electrical and thermal conductivity. There are several different copper foil materials available for this purpose. Copper foil is available in two basic types: wrought and electrodeposited. Rolled copper foil is most common, while the thinner electroplated copper foil is becoming popular.