PCB Fabrication – The Basics

PCBA printed circuit board is a mechanical support which connects different electronic components through the use of conductive pads, tracks and other elements engraved from copper sheets which were laminated on a substrate that’s non-conductive. PCBs are often categorized according to layer quantity. Multi-layer PCBs permit larger component density. Advanced printed circuit boards could include parts such as resistors, capacitors or active mechanisms inserted in the substrate. Moreover, the conductors on each of the layers are attached with vias which are plated-through holes.

PCB fabrication processes differ on each of the layer classifications. Each layer also has specifications for its circuits.

For single layer:

1. The maximum size of its circuit should be 8” x 8”

2. Minimum line width of 6 mils

3. 0.5 inch connector spacing

4. Minimum line gap is 6 mils

5. The text on each layer should have a minimum height of 80 mils and a track width of 8 mils

6. Gerber RS – 274X, precision 7. The origin must be located at the lowest left corner of the draft

8. A 200 x 200 x 20 mils cutting marks

Single layers which contain vias are also the same as single layer. However, there is a difference between the riveted vias and the plated vias. The specifications for each are as follows.

Riveted vias:

1. Riveted vias should only be used when the circuit contains less than 15 holes

2. A diameter size of 31 mils for each hole

3. 60 mils diameter pad

4. The center of the pad must be uncovered

Plated vias:

1. Plated vias should only be used when the hole size is critical or the holes on

2. The circuits are of large quantity

3. The maximum circuit size is 6” x 6”

4. The laser cutting area is only limited to 3.75 x 3.75

5. A minimum aspect ratio of 2:1

6. A .dfx file for holes with a precision of 2.4

7. The layout file is already filled with holes

8. Three alignment holes of 66/120 mils dia with donuts outside of the draft

9. A clearance of 10 mils

10. The center of the pad is covered

For multiple layer:

1. A 3D drawing is needed to represent the whole circuit

2. Plated hole is possible and an inner connection could also be possible

3. If connection between two substrates is needed, a plated via is required

4. The maximum size is 2” x 5”

5. A text must be printed on each layer

6. Gerber file scale 1 required on each layer

7. The first substrate must be positioned on the bottom

8. 0.125” diameter pins must be used for the alignment between substrates at a 2.5” center to center distance

9. The drill file should be limited to 3.75” x 3.75” and must be in .dxf form

Included in the manufacturing of a PCB is the PCB fabrication. PCB fabrication involves the PCB material, etching tanks, and many more. Basically, PCB fabrication is done by CAD. The Gerber or Excellon filed in the fabrication data are usually read by the Computer Aided Manufacturing software or CAM software.

Some of its principal functions are:

1. Gerber data input

2. Data verification; optional DFM

3. Reparation for the digression that exist in the manufacturing processes (e.g. scaling to compensate the alterations during lamination process)

4. Panelization

5. Output of the digital devices such as drill files, copper patterns, electrical test files, legend image, solder resist image, automated optical inspection data, etc.)

All in all, making PCBs isn’t as simple as many believe it to be; still, with the right steps and components, accomplishing such a task is far from impossible.

One Comment

  1. Malcolm Wagner May 17, 2016

    Wonderful Post…I like it…!!
    After reading this post i get an idea about PCB fabrication processes differ on each of the layer classifications and also gives the various types of PCBs layers…Read this post it give some of its principal functions…Click here Pcbnet foe more details about PCBs layers…Great work!!!

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