PCB design layers meaning

Before we proceed with the PCB design, the first step is to choose the right working layer. Protel 99 SE offers several types of working layers. Only after understanding the functions of these working layers can the printed circuit board design be accurate and reliable.

The working layers provided by the Protel 99 SE can be broadly categorized into seven categories: Signal Layers, Internal Planes, Mechanical Layers, Masks, Silkscreen Layers), Others (Working Layers) and System (Working Layers), execute menu commands during PCB Design [Design] Design / [Options ...] Options to set the visibility of each working layer.

1. Signal Layers

Protel 99 SE provide 32 signal layers including TopLayer, BottomLayer, MidLayer1, MidLayer2, ... [Mid Layer 30]. The signal layer is mainly used to place the components (top and bottom) and traces. The signal layers are positive, ie the traces or other objects placed on these working planes are copper-clad areas.

2. Internal Planes 

The Protel 99 SE supply 16 internal power / ground planes (referred to as the internal plane): [InternalPlane1] - [InternalPlane16]. These working planes are dedicated to power lines and a ground lines. The traces or other objects placed on these planes are copper-free, ie the working layers are negative * (negative). Each internal power/ground plane can be given an electrical network name, and the board editor automatically connects this level with other pads of the same network name (ie, electrical connections) in the form of pre-cords. In Protel 99 SE. It also allows you to divide the internal power/ground plane into multiple sub-layers, ie each internal power/ground plane can have two or more power supplies such as +5 V and +15 V and so on.

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3. Mechanical Layers

There are 16 mechanical layers available in the Protel 99 SE: [Mechanical1] - [Mechanical16]. The mechanical layer is typically used to place information on board and assembly methods, such as circuit board physical dimensions, dimensional markings, datasheets, Hole information, assembly instructions, and other information.

4. Masks (solder mask, solder paste protective layer)

In Protel 99 SE there are 2 solder masks: [Top Solder] and Bottom Solder. The solder mask is negative and the solder placed on this layer Trays or other objects are copper-free areas. Generally, in order to meet manufacturing tolerances, manufacturers often require the designation of a solder mask expansion rule to enlarge the solder mask. For different requirements of different pads, in the solder mask There are multiple rules that can be set and the Protel 99 SE also provides two layers of solder paste that are [Top Paste] and [Bottom Paste]. The solder mask functions similarly, but when using "hot re-follow" technology to mount SMD components, the solder mask is primarily used to create a silkscreen of the solder mask that is also positive. Similar to the solder layer, we can also enlarge or reduce the solder paste by specifying an extension rule. For different requirements of different solder pads, multiple rules can also be set in the solder paste protection layer.

5. Silkscreen (silk screen layer)

Protel 99 SE comes with 2 silkscreen, Top Overlay and Bottom Overlay. Silk screen layer is mainly used to draw the outline of the components, placing the number of components or other text messages. When a PCB library component is placed on a printed circuit board, the component number and outline are automatically placed on the silkscreen.

6. Others (other work level)

In Protel 99 SE, in addition to the above working planes, there are the following working layers: [KeepOutLayer] Prohibit Wiring Layers are used to define the area where components are placed. Normally, we place a track or arc on the no-lamination wiring layer to form a closed area where automatic component placement and routing are allowed. Note: If you want to auto-route part or all of the circuits, then you need to define at least one forbidden wiring area on the forbidden wiring layer. [Multilayer] This layer represents all the signal layers, and the components placed on it are automatically placed on all the signal layers, so we can use [MultiLayer] to connect the pads or through-vias Place quickly on all signal layers. Drill guide Drill drawing Protel 99 SE is provided with 2 drill hole positions, Drill guide and Drill drawing, ), These two layers are mainly used to draw the drilling map and drilling location. The Drill Guide is primarily intended to be compatible with manual drilling and older circuit board fabrication, and Drill Drawing is more often used to provide drilling references for modern manufacturing processes. We generally place the specified information for the hole in the Drill Drawing working layer. The drilling information is included in the printout when generating the drilling file, and a code map of the drilling locations is generated. It is often used to produce a drawing of how to make circuit boards.

Here to remind everyone Note:

(1) Drilling information that is automatically generated at output is visible in the PCB document, regardless of whether or not the Drill Drawing working layer is set to visible.

(2) The [Drill Drawing] layer contains a special ".LEGEND" string, which, when printed, determines where the drill map information is generated.

7. System (system working layer)

[DRC Error Layer]

Used to display information that violates the design rules check. While this layer is off, DRC errors will not be visible on the workspace screen, but the online design rule checking will still work. [Connections] This layer is used to display the electrical connections between objects such as components, pads, and vias, such as the Broken Net Marker or Ratsnest, but the Track does not contain In it. When the layer is closed, these connections are not displayed, but the program still analyzes its internal connections. [Pad Holes] When this layer is opened, the inner hole of the pad will be shown on the drawing. [Via Holes] When this layer is opened, the inner hole of the via hole is shown on the figure. [Visible Grid 1] Visible Grid 2 These two items are used to display grid lines. The corresponding grid spacing can be set as follows: Execute the menu command [Design ] / [Options ...], the visible grid spacing can be set in [Visible 1 [Visiblc 2] in the popup dialog box.