How to make a PCB – an ExpressPCB Tutorial (Part 2)
Lets proceed to making the layout itself. At this point,i am assuming that you have a .sch (Schematic) file ready with you.
- Fire up ExpressPCB (and not ExpressSCH).
- Before we move on to the layout,some basics about PCB’s. A pcb can be of different types-single layered,2 layered,4 layered. A layer basically means that traces(copper connections) will be present on the surface. So a single layered pcb has copper traces only on upper surface,a 2 layered pcb has traces on upper and lower surfaces.
- A single layered pcb is advised for most of the applications,whether you are making a board which has a 40 pin IC or anything else. This is bcoz it is cheaper.
- However,if you are using RF components of high frequency,then you should probably be using 2 or 4 layered PCB’s .This is becoz there are some issues regarding Power Planes and Ground Planes.
- ExpressPCB has 2 options-2 layered or 4 layered.
- This tutorial will deal with making 2 layered PCB’s only.
- Click —–>File—->New—->2 Layers—->Ok.
- Then click —-> File—->Link Schematic to PCB—–> (Select your .sch schematic file)—->ok
- Now remember this…anything in RED is on the upper surface of your board,while anything in GREEN is on the lower surface. Anything in YELLOW means that it is ‘silk’ or just the name or label of a component.
- Keeping everything in either only RED or only GREEN will make your board single layered. If you have traces in both red and green,it will make your board 2 layered.
- Rest of the interface is similar to ExpressSCH, only here you have ‘Place Trace’ instead of ‘Place wire’. also there is an additional option of ‘Place Pad’. A ‘pad’ is a hole in your board. It connects the upper layer to lower layer.Components are inserted through holes. Placing pads in your ground and Vcc traces at regular intervals is recommended.
- Lets proceed with making a layout for the Voltage regulator whose Schematic we made yesterday.
- Click—-> Component Manager—->Semiconductor-TO 92—->Insert Component into PCB
- Then place the capacitors. For capacitors, leading space of 4.5mm is sufficient for disc and electrolytic capacitors. For resistors, keep leading space of 0.5 inch. Note that we aren’t using SMD’s over here,just normal components.
- Now double click on each component. Assign EACH of them the SAME PART ID that was assigned in the schematic(.sch). For eg,we named the capacitors C1 and C2. So give them the same names in the layout. You can see i have done that in the above picture.
- Click—–>Place a trace—->Then click on one terminal of C1. You will see 2 BLUE marks appearing. One at the C1 terminal and other at the Regulator terminal. BLUE marks indicate that these 2 are to be connected together.
- Connect all terminals together as per the dots shown.
- Now to make some of the traces thicker,double click on each one—>Trace type—>Select the Width
- The main Vcc and Ground Trace should be made thicker than the others. Check out the pic below. Also ,if you want to draw a trace on the lower surface,select the Green icon with arrows pointing downwards. Check pic below. Don’t forget to place ‘Pads’ at regular intervals in the traces.
- Good. Your nearly done. Re-size the yellow border(outline) of the PCB to make it as small as possible. A SMALLER pcb is a CHEAPER pcb. But take care that its not so small,that you find it difficult to solder components.
- Congratulations ! Take a print out of the layout,and give it to some professional PCB maker. It’ll be done real cheap. An AVR development board layout that i made myself cost me only Rs. 80 (less than US 2$).
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