Point-to-point construction - AbsoluteAstronomy.com

Point-to-point construction refers to the method in which electronics

Electronics

Electronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...

circuits

Electronic circuit

An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow...

were constructed before the 1950s. Point-to-point construction is still used to construct prototype equipment with few or heavy electronic component

Electronic component

An electronic component is a basic electronic element and may be available in a discrete form having two or more electrical terminals . These are intended to be connected together, usually by soldering to a printed circuit board, in order to create an electronic circuit with a particular function...

s.

Before point-to-point connection, electrical assemblies used screw

Screw

A screw, or bolt, is a type of fastener characterized by a helical ridge, known as an external thread or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as an internal thread, often in the form of a nut or an object that has the...

s or wire nuts to hold wires to an insulating wooden or ceramic board. The resulting devices were prone to fail from corroded contacts, or mechanical loosening of the connections. Early premium marine radios, especially from Marconi

Marconi Company

The Marconi Company Ltd. was founded by Guglielmo Marconi in 1897 as The Wireless Telegraph & Signal Company...

, sometimes used welded copper in the bus-bar circuits, but this was expensive.

Point-to-point construction uses terminal strips (sometimes called 'tag boards') or turret board

Turret board

Turret boards were an early attempt at making electronic circuits that were relatively rugged, producible, and serviceable in the days before printed circuit boards...

s.
The crucial invention was to apply soldering

Soldering

Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a lower melting point than the workpiece...

to electrical assembly. In soldering, an alloy of tin

Tin

Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...

and lead

Lead

Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

, or later bismuth

Bismuth

Bismuth is a chemical element with symbol Bi and atomic number 83. Bismuth, a trivalent poor metal, chemically resembles arsenic and antimony. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The free element is 86% as dense as lead...

and tin

Tin

, is melted and adheres to other, nonmolten metal

Metal

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

s, such as copper

Copper

Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

or tinned steel

Steel

Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

. Solder makes a strong electrical and mechanical connection.

Terminal strip construction

Point-to-point construction uses terminal strips (also called 'tag boards'). A terminal strip is a stamped strip of tin-plated loops of copper. It is mounted in a way that electrically insulates

Electrical insulation

thumb|250px|[[Coaxial Cable]] with dielectric insulator supporting a central coreThis article refers to electrical insulation. For insulation of heat, see Thermal insulation...

each loop from the others. The metal loops are mounted on a cheap, heat-resistant material, usually synthetic-resin bonded paper (FR-2

FR-2

FR-2 is an abbreviation for Flame Resistant 2. It is a NEMA designation for synthetic resin bonded paper, a composite material made of paper impregnated with a plasticized phenol formaldehyde resin, used in the manufacture of printed circuit boards...

), or bakelite reinforced with cotton, or sometimes paxolin

FR-2

. The insulator has an integral mounting bracket, sometimes shorted to one or more of the stamped loops to ground them to the chassis.

The chassis

Chassis

A chassis consists of an internal framework that supports a man-made object. It is analogous to an animal's skeleton. An example of a chassis is the underpart of a motor vehicle, consisting of the frame with the wheels and machinery.- Vehicles :In the case of vehicles, the term chassis means the...

was constructed first, from sheet metal

Sheet metal

Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material...

or wood

Wood

Wood is a hard, fibrous tissue found in many trees. It has been used for hundreds of thousands of years for both fuel and as a construction material. It is an organic material, a natural composite of cellulose fibers embedded in a matrix of lignin which resists compression...

. Insulated terminal strips were then riveted, nail

Nail (engineering)

In woodworking and construction, a nail is a pin-shaped, sharp object of hard metal or alloy used as a fastener. Formerly wrought iron, today's nails are typically made of steel, often dipped or coated to prevent corrosion in harsh conditions or improve adhesion...

ed or screw

Screw

ed to the underside or interior of the chassis. Transformer

Transformer

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field...

s, large capacitor

Capacitor

A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...

s, Tube socket

Tube socket

Tube sockets are electrical sockets into which vacuum tubes can be plugged, holding them in place and providing terminals, which can be soldered into the circuit, for each of the pins. Sockets are designed to allow tubes to be plugged in in only one orientation...

s and other large components were mounted to the top of the chassis. Their wires were led through holes to the underside or interior. The wires of electronic components were physically looped through the terminals and soldered to them. Small electronic components were mounted by twisting their wire

Wire

A wire is a single, usually cylindrical, flexible strand or rod of metal. Wires are used to bear mechanical loads and to carry electricity and telecommunications signals. Wire is commonly formed by drawing the metal through a hole in a die or draw plate. Standard sizes are determined by various...

s around terminals

Terminal (electronics)

A terminal is the point at which a conductor from an electrical component, device or network comes to an end and provides a point of connection to external circuits. A terminal may simply be the end of a wire or it may be fitted with a connector or fastener...

and soldering.

Professional electronics assemblers used to operate from books of photograph

Photograph

A photograph is an image created by light falling on a light-sensitive surface, usually photographic film or an electronic imager such as a CCD or a CMOS chip. Most photographs are created using a camera, which uses a lens to focus the scene's visible wavelengths of light into a reproduction of...

s and follow an exact assembly sequence to assure that they did not miss any components. Although this process is error-prone and nearly impossible to automate, it is quite good for building small numbers of units when labor costs are low.

Point-to-point construction continued to be used for high quality tube

Vacuum tube

In electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...

electronics even after the invention 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. The American manufacturer Zenith continued to use point-to-point wiring in its tube based television sets until the early 1970s.

Today, audiophile equipment, such as amplifiers, may be point to point wired using terminal pins. Whilst many of these units are produced in very small quantities, it is perfectly possible for the public to produce commercial quality printed circuit boards using free design software and online prototyping printers. The point-to-point style is retained instead as mark of quality, as the connections between components are as thick as their lead out wires will allow and usually short, involving no tracks and few jumpers between points. This is desired as a common goal of audiophile equipment is to have the absolute minimum resistance possible where it is not controllable or needed, which is provided by the thick 'solid' wiring method; a common complaint against PCB layouts being that the tracks have a very small cross sectional area. Short, straight leads also produce the lowest values of inductance. With the leads being suspended in air, they have a minimal amount of capacitance, where as PCBs can suffer from capacitive effects between the layers. As silver is a slightly better conductor than copper, very expensive capacitors and resistors will be made from pure silver and feature silver lead outs. The slight increase in conductivity is not commercially worthwhile, or necessary, for the majority of electronics and so PCB manufacturers do not offer it as a standard option for the conductive material. But the point to point method allows the producer to have an essentially pure silver path between components.

As with the gain in conductivity when using copper, the electrical gains with regards to resistance, inductance, capacitance and so on are often of little importance to most electronics. However, they are extremely important at high frequencies, as frequency is a parameter in defining how currents and voltages interact with these properties. The effects can be so pronounced as to cause high frequency equipment to catastrophically fail with regards to performance if improperly laid out, regardless of component choice and the circuit's logic. As a result, it is still possible to see a direct, point-to-point, straight, heavy line layout used in high performance radio frequency equipment, particularly as the frequencies approach the gigahertz band. A blend of the two methods if used in many of these cases, where a ceramic board is used featuring tracks, but with the point-to-point layout logic. The difference between the values is small, and the audio spectrum is orders of magnitude below the radio frequencies, making the measurable difference between a PCB and point to point terminal method vanishingly minute in many cases. When the current is constant DC, the differences become essentially zero (bar the effect of DC resistance) as this has frequency of zero, meaning the inductances and capacitances are being multiplied by zero, which will give a zero result.

Despite its often superior electrical properties (and disregarding its bulky, often messy appearance), this method of wiring is by far and a way one of the most simple to put together and solder, as it has a basic nature to it and features large, easily handled and heated components and posts. More difficult than the actual assembly of a point-to-point board is usually the design, as boards are usually laid out as a 'ladder' of side by side elements, which may need connecting to others that aren't adjacent to themselves; requiring a jumper between the two. The art in a layout is the minimization of these jumpers (the wiring complexity).

This method of wiring (be it between terminals, components or leads) has one well known disadvantage in that the parasitic resistance of PCBs, poorer conductors and longer leads can actually add stability to a circuit. By reducing it close to zero, capacitive and inductive elements within the circuit may go into resonance, with the designer having to purposefully add a resistor at a later date.

Placing the completed unit in an enclosure protects it from mechanical damage when the chassis is mounted in a piece of furniture

Furniture

Furniture is the mass noun for the movable objects intended to support various human activities such as seating and sleeping in beds, to hold objects at a convenient height for work using horizontal surfaces above the ground, or to store things...

or an equipment rack, prevents foreign objects which may alter the electrical characteristics of the circuits and interfere with proper operation (such as by causing short circuits or altering electromagnetic fields), and protects humans and animals from contact with potentially dangerous voltages which may cause an electric shock while the machine is operating and from sharp edges and points on the assembly which could cause physical injury such as cuts.

Some large brand names still use point-to-point boards, but usually for special product lines. Marshall, who famously produce guitar amplifiers, have recently released reissues of their older models featuring point to point boards. At audio frequencies, it is highly debatable whether or not the any of the electrical gains of using this method are in any way tangible, but the method carries a weight of originality and solid, hands-on construction that implies more care and higher quality components have been used. Marshall's standard product line has been for many decades, and still is, PCB based. When it was realized mounting thermionic valves directly to the PCB caused heat issues, manufacturers of audio equipment like this began mounting the ceramic connectors for the valves on the metal chassis, running lead out wires to the PCB below. This allows them to mass produce the complex boards and still create a product that will last with a minimal amount of manual soldering involved.

'Dead bug' construction

For hobbyist work, free-form construction can be used in cases where a PCB would be too big or too much work for a small number of components. This is sometimes called "dead bug style" as the ICs

Integrated circuit

An integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...

are flipped upside-down with their pins sticking up into the air, evoking the image of the upturned body of an expired insect. While it is often messy-looking, error-prone, and difficult to repair, this can be used to make more compact circuits than other methods. This is often used in BEAM robotics

BEAM robotics

The word "beam" in BEAM robotics is an acronym for Biology, Electronics, Aesthetics, and Mechanics. This is a term that refers to a style of robotics...

and in RF circuits where component leads must be kept short. One advantage is the ease with which wire wrap

Wire wrap

Wire wrap is a technology used to assemble electronics. It is a method to construct circuit boards without having to make a printed circuit board. Wires can be wrapped by hand or by machine, and can be hand-modified afterwards. It was popular for large-scale manufacturing in the 60s and early 70s,...

connections may be made to components when resistor and capacitor leads are bent to a U shape and also glued in place.

External links

A picture of "dead bug style"
Progressive Wiring Techniques shows an example of point-to-point construction applied to surface-mount components.

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.

Terminal strip construction

'Dead bug' construction

See also

External links