PCB Tech - Introduction to PCB Factory PCB Design Related Concepts

Introduction to PCB Design Company PCB Design Related Concepts

Via:

Once a via is selected in the PCB design, be sure to handle the gap between it and the surrounding entities, especially the gap between the lines and the vias that are easily overlooked in the middle layers and the vias. If it is automatic routing, you can Select the "on" item in the Via Minimiz8tion submenu to automatically solve it. The larger the current-carrying capacity required, the larger the size of the vias required, such as the larger vias used to connect the power layer and ground layer to other layers.

Silk screen layer:

In order to facilitate the installation and maintenance of the circuit, the PCB design prints the required logo patterns and text codes on the upper and lower surfaces of the printed board, such as component label and nominal value, component outline shape and manufacturer logo, production date, etc. . When many beginners design the relevant content of the silk screen layer, they only pay attention to the neat and beautiful placement of the text symbols, ignoring the actual PCB effect. On the printed board they designed, the characters were either blocked by the component or invaded the soldering area and wiped off, and some of the components were marked on the adjacent components. Such various designs will bring a lot to assembly and maintenance. inconvenient. The correct principle for the layout of the characters on the silk screen layer is: "no ambiguity, stitches at a glance, beautiful and generous".

SMD package:

There are a large number of SMD packages in the PCB design software Protel package library, that is, surface soldering devices. The biggest feature of this type of device in addition to its small size is the single-sided distribution of pin holes. Therefore, when choosing this type of device, it is necessary to define the surface of the device to avoid "missing pins (Missing Plns)". In addition, the relevant text annotations of this type of component can only be placed along the surface where the component is located.

Filling area:

Grid-like filled area (External Plane) and filled area (Fill)

Just like the names of the two, the network filled area is to process a large area of copper foil into a network, and the filled area only keeps the copper foil intact. Beginners often can't see the difference between the two on the computer in the design process, in fact, as long as you zoom in, you can see it at a glance. It is precisely because it is not easy to see the difference between the two in normal times, so when using it, it is even more careless to distinguish between the two. It should be emphasized that the former has a strong effect of suppressing high-frequency interference in circuit characteristics, and is suitable for needs. Places filled with large areas, especially when certain areas are used as shielded areas, partitioned areas, or high-current power lines are particularly suitable. The latter is mostly used in places where a small area is required such as general line ends or turning areas.

Pad:

The pad is the most frequently contacted and most important concept in PCB design, but beginners tend to ignore its selection and modification, and use circular pads in the design. The selection of the pad type of the component should comprehensively consider the shape, size, layout, vibration and heating conditions, and force direction of the component. Protel provides a series of pads of different sizes and shapes in the package library, such as round, square, octagonal, round and positioning pads, but sometimes this is not enough and needs to be edited by yourself. For example, for pads that generate heat, are subjected to greater stress, and are current, they can be designed into a "teardrop shape". In the familiar color TV PCB line output transformer pin pad design, many manufacturers are just In this form.

Generally speaking, in addition to the above, the following principles should be considered when editing the pad by yourself:

(1) When the length of the shape is inconsistent, the difference between the width of the wire and the specific side length of the pad should not be too large;

(2) It is often necessary to use asymmetric pads with asymmetrical length when wiring between component lead angles;

(3) The size of each component pad hole should be edited and determined separately according to the thickness of the component pin. The principle is that the size of the hole is 0.2 to 0.4 mm larger than the pin diameter.

Various types of membranes:

These films are not only indispensable in the PCB manufacturing process, but also a necessary condition for component soldering. According to the position and function of the "membrane", the "membrane" can be divided into component surface (or soldering surface) soldering mask (TOp or Bottom) and component surface (or soldering surface) solder mask (TOp or BottomPaste Mask). As the name implies, the soldering film is a film that is applied to the pad to improve the solderability, that is, the light-colored round spots on the green board that are slightly larger than the pad. The situation of the solder mask is just the opposite, for To adapt the finished board to wave soldering and other soldering methods, it is required that the copper foil at the non-pad on the board cannot be tinned. Therefore, a layer of paint must be applied to all parts other than the pad to prevent tin from being applied to these parts. It can be seen that these two kinds of membranes are in a complementary relationship. From this discussion, it is not difficult to determine the settings of items like "solder Mask En1argement" in the menu.

The flying line has two meanings:

The rubber band-like network connection used for observation during the automatic routing of PCB design. After importing the components through the network table and making a preliminary layout, you can use the Show command to see the crossover status of the network connection under the layout. Adjust the position of the component to minimize this crossover to obtain the maximum automatic routing rate. This step is very important. In addition, after the automatic wiring is completed, which networks have not yet been deployed, you can also use this function to find out. After finding the unconnected network, it can be compensated manually. If it can't be compensated, the second meaning of "flying line" is used, which is to connect these networks with wires on the future printed board. If the circuit board is produced in a large-scale automatic line, this flying lead can be designed as a resistance element with a 0 ohm resistance value and a uniform pad spacing.