Manufacturing - Etching Process

MANUFACTURING -ETCHING PROCESS

ABSTRACT:

The process of converting raw materials, components, or parts into finished goods that meet a customer's expectations or specifications is called as Manufacturing. Manufacturing commonly employs a man-machine setup with division of labor in a large scale production. Etching is nothing but the art of preparing etched plates, especially metal plates, from which designs and pictures are printed. It can also be defined as Method of engraving in which lines or textures are bitten, or etched, into a metal plate, usually copper, with acid. The image produced has spontaneity of line that comes from drawing on the plate in the same direct way as with pen or pencil on paper. The first etchings date from the early 16th century, but the basic principle had been used earlier for the decoration of armour. When we hear the word manufacturing we all think about the manufacturing of big materials, but in this paper I have explained how the PCB (PRINTED CIRCIUT BOARD) is manufactured using etching process. As it is manufactured by etching process it can also be called as etched wiring board. In industry, etching is also known as chemical milling. In this paper we have discussed about manufacturing of PCB by etching process, surface mount technology etc.

History:

Development of the methods used in modern printed circuit boards started early in the 20th century. In 1903, a German inventor, Albert Hanson, described flat foil conductors laminated to an insulating board, in multiple layers. Thomas Edison experimented with chemical methods of plating conductors on linen paper in 1904. Arthur Berry in 1913 patented a print-and-etch method in Britain, and in the United States Max Schoop obtained a patent to flame-spray metal onto a board through a patterned mask. Charles Durcase in 1927 patented a method of electroplating circuit patterns. The inventor of the printed circuit was the Austrian engineer Paul Eisler who, while working in England, made one circa 1936 as part of a radio set. Around 1943 the USA began to use the technology on a large scale to make proximity fuses for use in World War II. After the war, in 1948, the USA released the invention for commercial use. Printed circuits did not become commonplace in consumer electronics until the mid-1950s, after the Auto-Sembly process was developed by the United States Army.

During World War II, the development of the anti-aircraft proximity fuse required an electronic circuit that could withstand being fired from a gun, and could be produced in quantity. The Centralab Division of Globe Union submitted a proposal which met the requirements: a ceramic plate would be screenprinted with metallic paint for conductors and carbon material for resistors, with ceramic disc capacitors and subminiature vacuum tubes soldered in place. In recent years, the use of surface mount parts has gained popularity as the demand for smaller electronics packaging and greater functionality has grown.

MANUFACTUING:

MATERIALS:

Conducting layers are typically made of thin copper foil. Insulating layers dielectric are typically laminated together with epoxy resin prepreg. The board is typically coated with a solder mask that is green in color. Other colors that are normally available are blue, black, white and red. There are quite a few different dielectrics that can be chosen to provide different insulating values depending on the requirements of the circuit. Some of these dielectrics are polytetrafluoroethylene(Teflon) etc.Well known prepreg materials used in the PCB industry are FR-2 (Phenolic cotton paper)

PATTERNING (Etching):

The vast majority of printed circuit boards are made by bonding a layer of copper over the entire substrate, sometimes on both sides, (creating a "blank PCB") then removing unwanted copper after applying a temporary mask (e.g. by etching), leaving only the desired copper traces. A few PCBs are made by adding traces to the bare substrate (or a substrate with a very thin layer of copper) usually by a complex process of multiple electroplating steps. The PCB manufacturing method primarily depends on whether it is for production volume or sample/prototype quantities

Commercial (production quantities, usually PTH):

* silk screen printing-the main commercial method.

* Photographic methods-used when fine linewidths are required.

Hobbyist/prototype (small quantities, usually not PTH):

* Laser-printed resist: Laser-print onto paper (or wax paper), heat-transfer with an iron or modified laminator onto bare laminate, then etch.

* Print onto transparent film and use as photomask along with photo-sensitized boards. (i.e. pre-sensitized boards), Then etch. (Alternatively, use a film photoplotter).

* Laser resist ablation: Spray black paint onto copper clad laminate, place into CNC laser plotter. The laser raster-scans the PCB and ablates (vaporizes) the paint where no resist is wanted. Etch. (Note: laser copper ablation is rarely used and is considered experimental.)

* Use a CNC-mill with a spade-shaped (i.e. 45-degree) cutter or miniature end-mill to route away the undesired copper, leaving only the traces.

There are three common "subtractive" methods (methods that remove copper) used for the production of printed circuit boards:

1. Silk screen printing uses etch-resistant inks to protect the copper foil. Subsequent etching removes the unwanted copper. Alternatively, the ink may be conductive, printed on a blank (non-conductive) board. The latter technique is also used in the manufacture of hybrid circuits.

2. Photoengraving uses a photomask and developer to selectively remove a photoresist coating. The remaining photoresist protects the copper foil. Subsequent etching removes the unwanted copper. The photomask is usually prepared with a photoplotter from data produced by a technician using CAM, or computer-aided manufacturing software. Laser-printed transparencies are typically employed for phototools; however, direct laser imaging techniques are being employed to replace phototools for high-resolution requirements.

3. PCB milling uses a two or three-axis mechanical milling system to mill