PCB Prototype or Prototyping

As we know for before producing the original market ready product we need to produce a prototype, in order to check whether it meets all the expectations. Therefore the printed circuit board prototype basically verifies that the design is right in various aspects of the customer, before the full scale production starts.  And if there is any error, it can be corrected without much loss of money and time. These prototypes can be sending for testing, so that other technical errors can be detected before the standard production run.

 

After prototypes are being made, and they have demonstrated their ability to meet with the required quality levels, then one can go for full production run. Sometimes, it may be desirable to go for a full production directly, and people assume that it is easy to deal with any sort of design flaws, as they will arise; it is not an efficient or economic solution.

 

Printed circuit boards are the main component of every product that switch on and off, lights up etc. Before prototyping, for PCB fabrication one needs to create Gerber files for prototype. Gerbers files are the blueprints that allow manufactures to build PCB by various prototyping techniques. Many design software available within the market, have built in tools for generating such prototyping files, ex. EAGLE, is one example which is used across the world and widely popular. One always has to keep in mind that following the common standards which offers cheap, fast and less complicated route for processing of prototype. Following design rule and standard must be followed:
(which are generally overlooked) in order to control the price and the yield.

 

1. Dimensions: The important part regarding this point is that the cost of printed circuit board is proportional to the surface area, and hence to the dimension of the printed circuit board. Irregular shapes are also required to be avoided, since it result waste of material, and hence the price increases.

Relay PCBA

2. Number of Layers:It indicates the complexity present within the printed circuit board. The Lamellar structure provides multiple paths for transmission of electrons, according to the requirement.

 

3. Type of Material: Printed circuit board consists of several copper clad which are fused together by suitable joining methods. Glass epoxy is most widely used nowadays. Each material has its specific properties therefore we use them according to the application. Across the world most of the manufacturer has the default choice of glass epoxy (FR-4), but it cannot be the case every time, because when case is of high speed designing where the dielectricity and thickness of material plays a vital role.

 

4. Board Thickness:As per standard the thickness of the board should be of order 1.6 mm. It can be varied, depending upon the number of copper layers; thickness can be less if space is limited. The lowest value of thickness is of order 0.4 mm.

 

5. Plating Finish:Plating is a technique in which the copper surfaces plated with another metallic material in order to improve the solderability during assembly. The plating technique used for Hot air solder welding, electroless nickel immersion gold plating.

Plating Finish

 

6. Impedance Control: For applications like wi-fi and Bluetooth designer need to specify the impedance control. Impedance control is nothing but the specified resistance to all signals travelling between them. Impedance depends upon various factors like dielectric of pre-prag, solder mask etc. Impedance control require expensive equipment, it cannot be done for all devices.

 

7. Minimum width/Spacing:In this the context is of width of copper traces over the printed circuit board, as well as the spacing between them. It has been an achievement to route out 64 or 128 pins from a microcontroller, but in this situation fabrication the limited spacing is challenge. And standard has also been defined for this also, like 6 mm spacing is very safe, some manufacturers also suggests 3-4 mm spacing.

Minimum width/Spacing

8. Hole Sizes:Holes are used to make connections between different layers, viz. vertical connection. It also creates some difficulty in fabrication. 0.2-0.3mm size of hole are quite typical and tight tolerance is also required to be followed.

 

9. Solder Mask:It is nothing but a layer of polymer over the copper traces of a printed circuit board. It avoids the problem of short circuiting between copper traces, or by other means. There are color choices also available. Green color was more favorable by most manufacturer, but during the processing of prototype the solder mask discolored because of high temperature flow and wave soldering. Therefore manufacturer switched to black in order to save the cost related to the cosmetic defects.

Solder Mask

 

10. Silkscreen:This the final layer applied over the printed circuit board which involves text, graphics, designations etc. which helps in annotations in documents of printed circuit board. The silkscreen sometimes used alternatively with legend printing. Liquid photo imaging technique is used to create silk screen, which usually develops high resolution legends of course with substantially higher cost.

Silkscreen

11. Minimum Pitch:Pitch refers to distance between adjacent pins on an electrical component. If the product is complicated and has lots of pins, it results very fine pitch. Therefore the manufacturing cost will go higher with the use of modern equipment.

There are different machines of different capabilities under different parameters ex. Quality grade, number of layers, build time, board size, board tolerance, solder mask type, aspect ratio, drilling hole diameter, surface finish, etc.

 

12. Benefits: The process of prototyping entails too many benefits. Some of them were paraphrased above. The major reason of prototyping is to check the design parameters, it appearance, various technical parameters without wasting money, material and time. Therefore all the flaws related to anything can be avoided.

  • Quick testing of printed circuit board prototype, and if any error detected, it can be fixed.
  • Clear indication about PCB functioning, and it also provides benefit from lower production tolerances.