Point-to-point construction

Terminal strip construction, which is often referred to as point-to-point construction within the tube guitar amplifier community, uses terminal strips (also called "tag boards"). A terminal strip has stamped tin-plated copper terminals, each with a hole through which wire ends could be pushed, fitted on an insulating strip, usually made of a cheap, heat-resistant material such as synthetic-resin bonded paper (FR-2), or bakelite reinforced with cotton. The insulator has an integral mounting bracket, sometimes electrically connected to one or more of the stamped loops to ground them to the chassis. The chassis was constructed first, from sheet metal or wood. Insulated terminal strips were then riveted, nailed or screwed to the underside or interior of the chassis. Transformers, large capacitors, tube sockets and other large components were mounted to the top of the chassis. Their wires were led through holes to the underside or interior. The ends of lengths of wire or wire-ended components such as capacitors and resistors were pushed through the terminals, and usually looped and twisted. When all wires to be connected had been fitted to the terminal, they were soldered together (and to the terminal). Professional electronics assemblers used to operate from books of photographs and follow an exact assembly sequence to ensure that they did not miss any components. This process is labor-intensive, subject to error and not suitable for automated production. Even after the introduction of printed circuit boards, it did not require laying out and manufacturing circuit boards. Point-to-point and terminal strip construction continued to be used for some vacuum tube equipment even after the introduction of printed circuit boards. The heat of the tubes can degrade the circuit boards and cause them to become brittle and break. Circuit board degradation is often seen on inexpensive tube radios produced in the 1960s, especially around the hot output and rectifier tubes. American manufacturer Zenith continued to use point-to-point wiring in its tube-based television sets until the early 1970s. Some audiophile equipment, such as amplifiers, continues to be point-to-point wired using terminal pins, often in very small quantities. In this application modern point-to-point wiring is often used as a marketing design feature rather than a result of the economics of very-small-scale production. Sometimes true point-to-point wiring—without terminal strips—with very short connections, is still used at very high radio frequencies (in the gigahertz range) to minimise stray capacitance and inductance; the capacitance between a circuit-board trace and some other conductor, and the inductance of a short track, become significant or dominant at high frequencies. In some cases careful PCB layout on a substrate with good high-frequency properties (e.g., ceramic) is sufficient. An example of this design is illustrated in an application note describing an avalanche transistor-based generator of pulses with risetime of a fraction of a nanosecond; the (few) critical components are connected directly to each other and to the output connector with the shortest possible leads. Particularly in complex equipment, wired circuits are often laid out as a "ladder" of side-by-side components, which need connecting to ladders or components by wire links. A good layout minimizes such links and wiring complexity, often approaching that of direct point-to-point. Amongst complex devices, the pre-PCB Tektronix vacuum-tube oscilloscopes stand out for their very well-designed point-to-point wiring. If parasitic effects are significant, point-to-point and terminal strip wiring have variable parasitic components, while the inductance and capacitance due to a PCB are the same for all samples and can be compensated for reliably which may be essential for some RF circuits. In some heavily optimised point-to-point RF constructions the circuit can be tuned by bending wires around. Placing the completed unit in an enclosure protects the circuit from its environment, and users from electrical hazards. A few large brand names still use terminal strip-type point-to-point boards, but usually for special product lines. Electric guitar amplifier manufacturer Marshall have reissued some of their older models, using this type of construction as a design feature, although their standard products have long used PCBs. Thermionic valve equipment usually does not have the valves mounted on the PCB in order to avoid heat damage, but instead use PCBs for the wiring, achieving the economy of mass-produced PCBs without the heat damage. ==Breadboard==

Prototypes which are subject to modification are often not made on PCBs, using instead breadboard construction. Historically this could be literally a breadboard, a wooden board with components attached to it and joined up with wire. More recently the term is applied to a board of thin insulating material with holes at standard 0.1-inch pitch; components are pushed through the holes to anchor them, and point-to-point wired on the other side of the board. A type of breadboard specifically for prototyping has this layout, but with strips of metal spring contacts beneath a grid of holes into which components are pushed to make electrical connections like any removable connector. Some portion of the terminals in a straight line in one direction are electrically connected, commonly in groups of 5-10 with multiple groups per row, these may be interspersed with columns that span the height of the board for the more common connections (typically the power supply rails). Such breadboards, and stripboards, fall somewhere between PCBs and point-to-point; they do not require design and manufacture of a PCB, and are as easily modified as a point-to-point setup. ==Stripboard==

A stripboard is a board with holes in square grid pattern, commonly with a 0.1-inch pitch; all the holes in a straight line are connected by a copper strip as on a PCB. Components are pushed through from the side without strips and soldered in place. The strips can be interrupted by scraping out a section of the copper, stripboard cutters are available for this task which are effectively a drill bit with a handle, they are used by rotating on the holes in a strip. == "Dead bug" construction ==

Free-form construction can be used in cases where a PCB would be too big or too much work to manufacture for a small number of components. Several methods of construction are used. At one extreme a wiring pen can be used with a perforated board, producing neat and professional results. At the other extreme is "dead bug" style, with the ICs flipped upside-down with their pins sticking up into the air like a dead insect, the leads of components are usually soldered directly to other components where possible, with many small circuits having no added wires. While it is messy-looking, free-form construction can be used to make more compact circuits than other methods. This is often used in BEAM robotics and in RF circuits where component leads must be kept short. This form of construction is used by amateurs for one-off circuits, and also professionally for circuit development, particularly at high frequencies. ==See also==