Although semiconductor integration more and more high, many applications are available on chip system, and many powerful and out of the box with the development board are increasingly available, but many use of electronic products in the case of applications still need to use a custom PCB. In a one-time development, even an ordinary PCB can play a very important role. PCB is the physical platform for design and the most flexible component for the design of electronic systems for primitive components. This article will introduce several PCB design of the golden rule, these laws since 25 years ago, the commercial PCB design was born, mostly without any change, and is widely used in various PCB design projects, both for electronic design engineers young or more circuit board manufacturers mature, has great guiding effect.
The following are the ten most effective design principles that should be kept in mind when designing an PCB layout and commercial manufacturing using an electronic design engineer. Engineers do not have to follow these rules in chronological or relative importance, and they can greatly change product design by simply following them all.
Rule one: select the right grid - set and always use the grid spacing that matches the most components. Although multigrid seems to be very effective, engineers can avoid the problem of interval setting and maximize the use of circuit boards if they can think more about it in the early stages of PCB layout design. Since many devices are available in a variety of package sizes, engineers should use products that are most conducive to their own design. In addition, the polygon for the circuit board copper is critical, multi grid circuit board will produce deviation polygon polygon filling in copper, although not based on a single grid as standard, but beyond the required service life of circuit board.
Rule two: keep the path shortest and direct. This may sound simple, but it should always be remembered at all stages, even if it means changing the layout of the circuit to optimize the length of the wiring. This is especially true for systems that are always limited in part to impedance and parasitic effects, analog and high-speed digital circuits.
Rule three: use the power layer to manage the distribution of the power line and the ground wire as much as possible. Power layer copper is the fastest and simpler choice for most PCB design software. By sharing a large number of wires, a current with the highest efficiency and minimum impedance or voltage drop can be guaranteed, while adequate ground return paths are provided. If possible, can also run a number of power lines in the circuit board in the same area, the ground is covered by PCB to confirm a certain level of most level, which is beneficial to the interaction between adjacent layers of the operation line.
Rule four: grouping the associated components with the required test points. For example: the discrete component OpAmp operational amplifier required placed in close position away from the device to bypass capacitor and resistor can with cooperation, to help optimize the wiring length rule 2 mentioned, but also makes the test and fault detection easier.
Rule five: the circuit board will be required in a larger circuit board duplication times PCB panel. Choosing the most suitable size for the equipment used by the manufacturer will help reduce prototyping and manufacturing costs. The first circuit board layout on the panel, the preferred size of contact circuit board manufacturer for each panel, and then modify the design specifications for you, and try to the panel size many times within your design.
Rule six: integrating component values. As a designer, you will choose some component values, or high or low, but discrete components of the same performance. The bill of material can be simplified and cost may be reduced by integrating within a smaller standard range. If you have a range of PCB products based on preferred device values, then, in the longer run, it will also help you make the right inventory management decisions.
Rule seven: execute the design rules check (DRC) as often as possible. Although the operation of DRC function in PCB software takes a very short time, but in the design environment more complex, as long as you are in the process of design always perform inspection and can save a lot of time, it is a good habit worth keeping. Each wiring decision is critical, and by executing DRC, you can always remind you of the most important cabling.
Rule eight: use screen printing flexibly. Screen printing can be used to mark various useful information for future use by circuit boards manufacturers, service or test engineers, installers or equipment commissioning personnel. Not only mark clear functions and test point labels, but also mark the direction of the components and connectors as much as possible, even if they are printed on the lower surface of the component used by the circuit board (after the circuit board is assembled). Full screen printing technology is applied to the lower and lower surfaces of the circuit board to reduce repetitive work and streamline production process.
Rule nine: mandatory decoupling capacitor. Don't try to optimize your design by avoiding decoupling the power line and according to the limits in the component data sheet. Capacitors are inexpensive and rugged, and you can spend as much time as possible on the capacitor assembly, and follow the rule six. Use the range of standard values to keep the stock in order.
Rule ten: generate the PCB manufacturing parameters and verify them before submitting them to production. Although most circuit board manufacturers are happy to download and verify it directly, you'd better first output Gerber files and check with the free reader as expected, so as not to cause any misunderstanding. By checking personally, you may even find some careless mistakes and avoid making production in the wrong parameters.
Because the circuit design is more and more widely shared, and internal teams increasingly rely on the reference design, the basic rules above will remain a feature of printed circuit board design, we believe that it is very important for the design of PCB. By defining these basic rules, developers can be very flexible in enhancing the value of their products and maximizing the gains from their circuit boards. Even novice circuit designers, as long as these basic rules are kept in mind, can speed up the learning process and increase confidence.
