Specifications
103
Pads are defined as a portion of a pattern on PCB‟s that are selected for the
purpose of surface mounting electrical components. The important topics
concerning pads involve their sizes, shapes, and dimensions. Pads heavily rely
upon the manufacturing process used to make the printed circuit board as well as
a person‟s solder ability. Another factor that is used to evaluate pads on a PCB is
known as the pad or hole ratio. More generally the pad or hole ratio is referring to
the pad size to hole size. The rule of thumb for the pad on the PCB should be 1.8
times the diameter of the hole because it will let the alignment tolerances on the
drill.
Using the PCB 123 software, the manufacturer has the option of choosing which
hole sizes he prefers best to implement on the printed circuit board. Make sure to
notice that when picking a hole size the plate-through will directly result in making
a hole narrow. These plate-through thickness of the holes range from 0.001
inches to 0.003 inches.
Another design rule to consider when making a PCB is trace width and spacing.
The trace width of the PCB depends upon the maximum temperature rise of
current and as well as the impedance tolerance. The least width of trace and
spacing are factored upon the x/y rules. X stands for the least trace width and y
is the least trace spacing.
Tracing spacing is an important parameter to discuss when trying to make a
PCB. It will tell the designer how to layout the traces width and spacing between
the holes. When a manufacturer makes a PCB he has to make sure that you are
given adequate spacing, so if the traces are adjacent to the holes there is a
possibility that they will be shorted and therefore the board will be no longer good
to use. To calculate the spacing requirements one must determine the peak
voltage and then plug it into the formula described below.
Trace Spacing
V
peak
= peak voltage (in Volts)
To find peak voltage in terms of Root - Mean Square Voltage:
Often when setting a workspace for the development of the PCB, people must
lay your board on a fixed grid, called a “snap grid.”This will function in order to
make all the components on the PCB snap into their permanent positions on the
grid. Another grid to question whether a developer would want to use is a visible
grid. A visible grid consist of an on-screen grid of solid lines or dots. Here are
some facts to bear in mind when working on grids for the design of PCB‟s.
- A snap grid is crucial because the workspace for the PCB will allow the
parts being placed on the board to be neat and well organized.