Though the PCB started in a very crude form, the technology has improved over the years and the present practices are much mare advanced and effective than the primitive ones. The change has been a gradual one and the approaches have been modified gradually over the years to its present form. This article is an attempt presenting the chronology.
- 1903 : Albert Hanson proposed depositing flat foils in multiple layers on an insulating substrate.
- 1904 : Thomas Edison attempted electroplating conductors on a linen paper.
- 1913 : Arthur Berry patented a print and etch method.
- 1913 : Max Schoop patented a method of flame spraying metal onto a substrate.
- 1927 : Charles Durcase patented a method to electroplate circuit patterns.
The earliest commercial approach
Dr. Paul Eisler invented the first PCB while working in England in 1936.
Later, the U.S Army started large scale production of PCBs utilize in proximity fuse in World War II. The development of anti-aircraft proximity fuse required the use of a circuit that could be fired from a gun and one that can be produced in large quantities. This led to the initial large scale production of PCBs. After the end of the war, the technology was released for commercial purposes.
- Early practice: Initially much emphasis was on the type and nature of the substrate used and any insulating substrate such as wood, plastic or paper was randomly used.
- Chemical etching: In this method, the substrate material is electroplated with copper, the circuit to be used is printed on the board and is then covered with acid resistant material. The work piece is then dipped in an etching solution and is agitated. The excess copper gets etched leaving behind useful tracks. The speed and efficiency of etching solution slowly decreases. Bubbles and splash methods are used to speed up the process.
- Cordwood construction: Cordwood construction was achieved by sandwiching the components between two etched PCBs. Although it reduced the space and gained a little mechanical strength, it was very difficult to troubleshoot the PCB. This approach became obsolete over time.
- Through hole construction: Initially the boards were pierced at requisite points where the components have to be soldered and the etch was done. The lead parts of the components were turned 90 degrees and inserted into the hole and soldered on the opposite side.
- Surface mount technology: To use the second side of the PCB that was rendered useless due to soldering, surface mount technology came into effect. In this approach, the components were designed in flat designs with the end leads and these could be placed and soldered on the same side of the board. This led to the utilization on both the sides of the PCB giving birth to double sided PCBs.
- Double sided PCBs: Both sides of the PCB started getting etched. The components were soldered on both the sides, or the second surface was dedicated to a particular purpose for example for applying the ground common to the circuit components. With this, the miniaturization of the PCB entered a new trend.
- Multilayer PCB: To reduce the dimensions further and add more features in the same size, manufacturers started stacking multiple layers of PCBs with an insulating laminate in between the layers. Often, certain layers were dedicated to a particular purpose only like a layer for power, one for ground and yet another for signals. Usually, 3-4 layers were stacked, but layers as high as 25 to 400 can be stacked according to he required application.
- 2.5D and PCB CAM : To achieve a high resolution of track designs and for miniaturization of dimensions, software came to the rescue for the cause. With the help of available software, designing the high resolution tracks became simpler and more complex designing cam now could be done to achieve greater economy in capital, size and features. Commonly used tools are ELIC, Genesis 2000, RS274-D & RS274-X.
The next generation technology
The next generation approaches witness the development of 3D printing to beneficially use the third dimension of the structure. This will also eliminate the problem of electronic reflection and interference and of limited data transfer capabilities.
New technologies are being developed to meet the needs of the rapidly changing technological scenario.