Newbie-PCB design--FIRST POST

[chimera786]

Hello guys..just downloaded and made my first pcb in diptrace. Im going to be doing the whole DIY pcb board..so i need to understand a few things.

1- What is a ground plane and why do I need it?

2- The pads dimensions are for the following parameters : Width, height and Hole. What physical proprieties of the pad do these parameters define.

3- What are the common values for the pad parameters . I want to use them when I make my first pcb so that I can get a hang of this.

Im really digging this software. Its for sure better than eagle, im my opinion. Thanks for reading guys!!!

 

[mister_rf]

1- What is a ground plane and why do I need it?

A ground plane in PCB assembly is a layer of copper that appears to most signals as an infinite ground potential. This helps reduce noise and helps ensure that all integrated circuits within a system compare different signals' voltages to the same reference potential.
It also serves to make the circuit design easier, allowing the designer to ground anything without having to run multiple tracks; the component needing grounding is routed directly to the ground plane on another layer.
Ground planes can also be placed on adjacent layers to power planes creating a large parallel plate capacitor that helps filter the power supply. Ground planes are sometimes split and then connected by a thin trace. This allows the separation of analog and digital sections of a board or the inputs and outputs of amplifiers. The thin trace has low enough impedance to keep the two sides very close to the same potential while keeping the ground currents of one side from impacting the other.

For the standard components, you need to check the suppliers recommendations pad sizes to follow and those are readily available on the internet. Some factors need to be considered determining the dimensions of the solder pads as the part dimension tolerances, PCB production tolerances and for the SMD components need to consider also the accuracy-of-placement tolerances. A properly designed solder pad try to minimizes solder bridging while affording a strong and easily inspected joint. Sometimes these goals have conflicting dimensional requirements. You should also consider the limitations of the soldering process to be used. So the boards designed for wave soldering usually have slightly wider pads than those designed for reflow techniques. If you are going to solder the wires into through holes just make sure that your clearances are enough to avoid shorts and try and make the pad as long and skinny has possible so there is as much surface area to solder to as possible.

 

[nelsonys]

Hi Chimera,

I assumed those routing theories and current flowing theories for PCB are easily found by you through various kinds of books and info available online.
If you are doing plain DC or usual analog board, it is not necessary to pour ground onto your board.

As you mentioned, this is your DIY board, I assume you do soldering by yourselves. There are major differences between handmade and machine-made PCB.

One obvious difference is how narrow you can achieve your clearance, follow by how thin can you fabricate your trace.
My experience is try not to challenge small pitch components for example, TSSOP.

You might think that TSSOP is still not that hard to achieve. But what about soldering? IC with TSSOP package usually needs a lower temperature heat profile not more than 300 degree celcius for more than 6 seconds (refer to datasheet). Besides do you have such fine tip soldering iron to do so (it's somewhat expensive)? Make sure you are using a temperature-controlled soldering station or at least, a soldering iron lesser than 25W, say 18W.

It makes sense that you are not going to make something like QFP and BGA on the board. I have a hard time trying to solder QFP manually using blower.
Therefore I would suggest SOIP only.

Talking about the pad parameters, libraries provided by the software usually follow the same pattern as in AXIAL 0.X, RADIAL 0.X and so on...
I do not know whether you came across these terms or not, I would like to briefly introduce about it.

Axial represents those components in "lying" condition, like resistors, diodes, etc. Bending of pins is needed for inserting into the PCB.
Radial represents those components in vertical standing condition, aluminium electrolytic capacitors, diode bridge, etc. Usually bending is not needed.
0.X represents the hole size which depends on your needs. Try not use up to 2 decimal places for your case, as you rarely find drill bits with such detail size in nearby shops.

You will need reworking in the future for debugging of circuit. That's why for handmade PCB, it is suggested to create a pad size with larger hole for easier desoldering. For eg, 0.5mm pin diameter into a 1mm hole with a pad size of 1.5mm. Some people might think that it's a bit large and loose for a resistor pin. I wouldn't say so. I experienced that small hole size will just make your life harder during desoldering, you might accidentally tear off the pad with small pad size.

It's recommended to apply teardrops on your pads to strengthen them on the board follow by wider trace to prevent over-etching.

 

[marce]

How to be a Circuit Board Designer

 

[marce]

search for:
"IPC-7351"
"Cad Library of the Future"