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The 7 Right Steps to Design an Excellent PCB?

A good PCB design company has a complete set of PCB design processes. MIV Solutions is a IDH PCB design company specializing in smart hardware electronic product design (layout wiring design). It has a PCB design team with an average of more than 10 years of work experience. Customers provide efficient and high-quality PCB design services.

MIV Solutions PCB design process is as follows: preliminary preparation-> PCB structure design-> PCB layout-> wiring-> wiring optimization and screen printing-> network and DRC inspection and structural inspection-> plate making.

First: preliminary preparation

This includes preparing component libraries and schematics. "Workers must first sharpen their tools if they want to do their job well." To make a good board, in addition to designing the principles, you must also draw well. Before the PCB design, we must first prepare the schematic SCH component library and PCB component library. The component library can use protel.

Second: PCB structure design

In this step, according to the determined circuit board size and various mechanical positioning, draw the PCB surface in the PCB design environment, and place the required connectors, buttons / switches, screw holes, assembly holes, etc. according to the positioning requirements. And fully consider and determine the wiring area and non-wiring area (such as how much range around the screw hole belongs to the non-wiring area).

Third: PCB layout

To put it bluntly, is to put the device on the board. At this time, if the preparatory work mentioned above is completed, you can generate a netlist (Design-> Create Netlist) on the schematic diagram, and then import the netlist (Design-> Load Nets) on the PCB diagram. I saw the full stack of the device clamoring, and there were flying leads between the pins to prompt the connection. Then the device can be laid out. The general layout is as follows:

1. Reasonable division according to electrical performance, generally divided into: digital circuit area (that is, fear of interference and interference), analog circuit area (fear of interference), power drive area (interference source);
2. The circuits that accomplish the same function should be placed as close as possible, and the components should be adjusted to ensure the most concise connection; at the same time, the relative position between each functional block should be adjusted to make the connection between the functional blocks simplest;
3. For high quality components, the installation location and installation strength should be considered; the heating element should be placed separately from the temperature sensitive element, and if necessary, thermal convection measures should also be considered;
4. The I / O drive device should be as close as possible to the side of the printed board and close to the leading connector;
5. The clock generator (such as: crystal oscillator or clock oscillator) should be as close as possible to the device that uses the clock;
6. Between the power input pin and ground of each integrated circuit, a decoupling capacitor (generally a monolithic capacitor with good high-frequency performance) needs to be added; when the circuit board space is dense, it can also be around several integrated circuits Add a tantalum capacitor;
7. Discharge diode (1N4148 is enough) at the relay coil;
8. The layout needs to be balanced, dense and orderly, not top-heavy or heavy. What is the PCB design process of a good PCB design company?

Need special attention

When placing components, be sure to consider the actual size of the components (occupied area and height) and the relative position between the components to ensure the electrical performance of the circuit board and the feasibility and convenience of production installation. Under the premise of ensuring that the above principles can be reflected, the placement of devices should be appropriately modified to make them neat and beautiful. For example, the same devices should be placed neatly and in the same direction.

This step is related to the overall image of the board and the difficulty of the next wiring, so it takes a lot of effort to consider. When laying out, you can make preliminary wiring for the less sure place first, and fully consider.

Fourth: wiring

Wiring is the most important process in the entire PCB design. This will directly affect the performance of the PCB board. In the PCB design process, there are generally three such divisions of wiring:

The first is routing, at this time the most basic requirements in PCB design. If none of the lines are routed and you can get flying lines everywhere, it will be an unqualified board.

The second is the satisfaction of electrical performance. This is a measure of whether a printed circuit board is qualified. This is after wiring, carefully adjust the wiring so that it can achieve the best electrical performance.

Then comes the beauty. If your wiring is laid, there is nothing that affects the performance of electrical appliances, but at a glance the messy past, plus the colorful, colorful, then how good your electrical performance, in the eyes of others is still a piece of garbage. This brings great inconvenience to testing and maintenance. The wiring should be neat and uniform, and can not be crisscrossed and unruly. These must be achieved under the condition of ensuring the performance of electrical appliances and meeting other individual requirements, otherwise it will be a waste of money.

The wiring is mainly carried out according to the following principles:

1. Under normal circumstances, the power cord and ground wire should be wired first to ensure the electrical performance of the circuit board. Within the scope of the conditions, try to widen the width of the power supply and the ground wire. It is better that the ground wire is wider than the power wire. Their relationship is: ground wire> power wire> signal wire, usually the signal wire width is 0.2 ~ 0.3mm , The thinnest width can reach 0.05 ~ 0.07mm, the power cord is generally 1.2 ~ 2.5mm. For the digital circuit PCB, a wide ground wire can be used to form a loop, that is, to form a ground network to use (analog circuit ground cannot be used in this way)

2. Route the stricter lines (such as high-frequency lines) in advance, and the side lines of the input and output should avoid adjacent parallel to avoid reflection interference. Ground wire isolation should be added when necessary, and the wiring of two adjacent layers should be perpendicular to each other, and parasitic coupling is likely to occur in parallel.

3. The shell of the oscillator is grounded, the clock line should be as short as possible, and can not be led everywhere. The area of the special high-speed logic circuit under the clock oscillation circuit should increase the area of the ground, and should not take other signal lines to make the surrounding electric field approach zero;

4. Use 45o polyline wiring as much as possible. Do not use 90o polyline to reduce the radiation of high-frequency signals; (requires high lines to use double arcs)
5. Do not form a loop in any signal line. If it is inevitable, the loop should be as small as possible; the vias of the signal line should be as few as possible;
6. The key line should be as short and thick as possible, and add protective grounds on both sides.
7. When transmitting sensitive signals and noise field-band signals through a flat cable, the "ground wire-signal-ground wire" method should be used.
8. Test points should be reserved for key signals to facilitate production and maintenance testing.
9. After the schematic wiring is completed, the wiring should be optimized; at the same time, after the preliminary network inspection and DRC inspection are correct, fill the unwired area with a ground wire, use a large area copper layer for the ground wire, and put it on the printed board. All unused places are connected to the ground for grounding. Or it can be made into a multi-layer board, and the power supply and ground wire each occupy one layer. What is the PCB design process of a good PCB design company?

PCB wiring process requirements 1. Line

In general, the signal line width is 0.3mm (12mil), and the power line width is 0.77mm (30mil) or 1.27mm (50mil); the distance between the line and the line and the pad is greater than or equal to 0.33mm (13mil) ), In practical applications, the distance should be increased when conditions permit;

When the wiring density is high, it can be considered (but not recommended) to use two lines between the IC feet, the width of the line is 0.254mm (10mil), and the line spacing is not less than 0.254mm (10mil). In special cases, when the device pins are dense and the width is narrow, the line width and line spacing can be appropriately reduced. 2. Pad (PAD)

The basic requirements for pads (PAD) and transition holes (VIA) are: the diameter of the disk is greater than 0.6mm than the diameter of the hole; for example, for general-purpose pin-type resistors, capacitors, and integrated circuits, the size of the disk / hole is 1.6mm / 0.8 mm (63mil / 32mil), socket, pin and diode 1N4007, etc., using 1.8mm / 1.0mm (71mil / 39mil). In actual application, it should be determined according to the size of the actual component. When conditions permit, the pad size can be increased appropriately;

The component mounting aperture designed on the PCB board should be larger than the actual size of the component pins by about 0.2 to 0.4 mm.

3. Via (VIA)

Generally 1.27mm / 0.7mm (50mil / 28mil);
When the wiring density is high, the size of the via hole can be reduced appropriately, but it should not be too small. 1.0mm / 0.6mm (40mil / 24mil) can be considered.

4. The spacing requirements of pads, lines and vias
PAD and VIA: ≥ 0.3mm (12mil)
PAD and PAD: ≥ 0.3mm (12mil)
PAD and TRACK: ≥ 0.3mm (12mil)
TRACK and TRACK: ≥ 0.3mm (12mil)

When the density is higher:
PAD and VIA: ≥ 0.254mm (10mil)
PAD and PAD: ≥ 0.254mm (10mil)
PAD and TRACK: ≥ 0.254mm (10mil)
TRACK and TRACK: ≥ 0.254mm (10mil)

Fifth: wiring optimization and screen printing

"There is no best, only better"! No matter how you think about the design, after you finish painting, and then take a look, you still feel that many places can be modified. The general design experience is that the time for optimizing wiring is twice the time for initial wiring. After feeling that there is nothing to be modified, you can lay copper (Place-> polygon Plane). Copper laying generally lays ground wires (note the separation of analog ground and digital ground), and may also need to lay power when multi-layer boards. For screen printing, be careful not to be blocked by the device or removed by vias and pads. At the same time, when designing, we should look squarely at the component surface, and the characters at the bottom should be mirrored to avoid confusion.

Sixth: Network and DRC inspection and structural inspection

First of all, on the premise of confirming that the circuit schematic design is correct, the generated PCB network file and the schematic network file are subjected to a network check (NETCHECK) of the physical connection relationship, and the design is corrected in time according to the output file result to ensure the wiring The correctness of the connection relationship;

After the network check is passed correctly, the DRC check is performed on the PCB design, and the design is corrected in time according to the output file results to ensure the electrical performance of the PCB wiring. Finally, the mechanical installation structure of the PCB needs to be further inspected and confirmed.

Seventh: plate making

Prior to this, it is best to have a review process.

PCB design is a thought-provoking job. Whoever has the most thoughtfulness and high experience can design the board. Therefore, design must be extremely careful, fully consider all factors (such as easy maintenance and inspection, many people do not consider it), and strive for excellence, we can certainly design a good board.