PCB design engineers have grading basis: introduction, elementary, intermediate (ABC), and advanced.Let’s have a look at what level of yourself.

Jobs: entry-level PCB engineers

Capacity requirements:

1, to create a simple package, such as DIP10 ;

2, to master the basic operation of at least one PCB design software, and can develop simple wiring width and spacing ;

3, to make reasonable and orderly layout and routing for the PCB with 100 components and 200 network or less.

4, to do the routing manually or automatically under the rules made by others or yourself and modity the routing,and 100% completion and DRC is completely passed.

5, to have the knowledge of the basic mechanical structure and thermal design

6, to have some basic requirements for double-sided traces.

Work:

1, design and modification of simple PCB,such as simple structure of the front panel,small single chip system board, etc.

2, specified part lines in complex PCB

3, the related debugging of their own pcb design.

4, write related development and debug logs.

Job duties: responsible for the part designed by yourself in the PCB.

Jobs: primary PCB engineers

Capacity requirements:

1, according to the manual and physical ,produce more complex packages such as lighted RJ-45 seat and so on, and to ensure that the size of shape and PAD is entirely correct (according to physical measurements ,to ensure that at least it can be inserted);

2, a master of at least one PCB design software,and can make detailed routing rules independently or under the guidance of others.

3, make reasonable and orderly layout and routing for the single-sided,double-sided and multilayer PCB with 400 components and 1000 network or less.During the layout and routing,consider the requirement of thermal design, structural design, electromagnetic compatibility design, aesthetics in a timely manner.When he is not sure,he should ask the more advanced PCB engineers for help or discuss with them.

4, expertly do the routing manually or automatically under the rules made by others or yourself and modity the routing,and 100% completion and DRC is completely passed.Basically there is no bottleneck of line width and the inner islands and other issues.During the routing ,he can find the stupid mistake on the principle of design and put forward the mistakes,and can correctly swap the pin and gate,and can correctly modify netlist and schematic.

5, correctly import and export mechanical drawings and basically understand structure size requirements;

6, He can proceed some high-speed and simulation PCB design under the rules or the guidance setted by others and basically stable

7, silk screen is clear.Independently complete design output work,such as Gerber, and proofread.

8, have a basic manufacturability aspects knowledge and use it for practice.More than 50% designed board can be used for production.

Work:
1, more complex PCB design and modification (eg scheduler boards in addition to CPU board , etc.);

2, specified part lines in complex PCB

3, the related debugging of their own pcb design.

4, for the work guidance of all lower-level PCB engineer;

5, write related development and debug logs.

6,if necessary,(that is to say you temporarily have no design task at a certain time,or some PCB design time is pressing,and we must transfer or strengthen the designer) you do the work of any low-level PCB engineer .

Job duties: responsible for the part designed by yourself in the PCB.

Jobs: intermediate PCB engineers (according to individual ability,it is subdivided into A, B, C three gears. A is supreme and B is the second)

Capacity requirements:
1, fully understand the various original components manuals and wiring manuals.Independently produce extremely complex packages such as placing the switch, and ensure that the capabilities entirely correct (according to physical measurements, ensure that at least the insertion).According to the principles and structural requirements on their own, find the right device or replacement

2,a skillful master of operation and skills of at least one PCB design software,and can make detailed routing rules .

3, put forward division and integration idea of various functional blocks according to the system requirements. Make reasonable layout and routing for any PCB with many components and network independently or cooperatively.During the layout and routing,consider the requirement of thermal design, structural design, SI,PI,EMC,aesthetics,and manufacturability in a timely manner and propose solutions.Can provide requirements and rules of some layout and wiring for entry-level and junior engineers.

4, correctly do the lamination design for PCB.Under the requirement that satisfy the performance ,try to minimize the number of layer and reduce the cost.

5, with more high-speed PCB design and simulation knowledge in the aspect of resistance, delay, overshoot, crosstalk, circuit, signal circuit, surface integrity, the inner slot, signal termination.Independently or under the guidance of SI engineers,complete SI simulation and analysis of key signal and regional and provide the improvement suggest.

6, under rule driven,skillfully rout by manual or automatic and pass the modification.The whole plate has a certain beauty.During the routing ,he can find the stupid mistake of 80% on the principle of design and put forward the mistakes,and can correctly swap the pin and gate.

7, He can be an excellent communication with the principles and structural design engineers. He can understand more complex mechanical drawings.He can put forward some reasonal improvement suggest of some principles,component selection ,and structure related PCB,and help system design early success.

8,test points and silk screen marking are clear and error-free.He makes few stupid mistakes in PCB design.Generally not due to PCB design error which led to the revision.The feedback,provide by more than 90% pcb factory engineers, can be always resolved by himself.

9, with more manufacturability aspects knowledge and use it for practice.More than 70% designed board can be used for production.

Work:
1, very complex PCB designs and modifications (such as 8-channel DVR chassis, PC motherboards, etc.);

2, the related debugging of their own pcb design.the SI simulation of specified position.

3, for the work guidance and routing rules of all lower-level PCB engineer;

4, write related development and debug logs.

5, production and maintenance for unit internal PCB standard package libraries and standard wiring module;

6, if necessary, do the work of any low-level PCB engineer .

Responsibilities:
1,responsible for the part designed by yourself in the PCB.

2,responsible for the part designed by yourself in unit internal PCB standard package libraries and standard wiring module.

3,responsible for their own SI simulation results and solutions.

Jobs: Senior PCB Engineer

Capacity requirements:
1, a master of document conversion between variety of common pcb design software.The document can be used to modify basically.

2, familiar with all the requirements of high-speed and simulation PCB design.More than 80% boards, designed by himself or by others but under his instruciton ,have no related issues.

3, with skillful manufacturability aspects knowledge and use it for practice and gudance work.More than 90% boards ,designed by himself or by others but under his instruciton ,can be used for mass production derictly.

4,skillful for high-density layout and routing under the high-speed rules.The module or board should be stable and reliable,and the same time,more than 80% board have great beauty.

5, very innovative, can often make various constructive proposals to improve PCB design efficiency, PCB design quality, PCB structure allocation in system.

Work:
1, to participate analysis, planning and simulation related to PCB in system design.

2, organize and carry out PCB design training;

3,for the work guidance and routing rules of all lower-level PCB engineer;

4, write related development and debug logs.

5,search, establishment, and file of SI simulation model.

6, SI, PI, EMC simulation of the entire board and system.Evaluation of PCB manufacturability . Analysis of defective PCB, and provide the effectibe solutions.

7, if necessary, do the work of any low-level PCB engineer.

Responsibilities:
1, responsible for all of their work;

2, responsible for guidance work of all the others.

First: preparation. This includes preparing component libraries and schematics. “To do a good job, one must first sharpen one’s tools”.To make a good board, in addition to good PCB design principles,drawing should also be well. Before PCB design,firstly component library of SCH schematic and PCB should be ready.Component library can use protel own libraries, but under normal circumstances it is difficult to find a suitable one.It is better to do the component library yourself according to the standard size data of the selected device. In principle, do first PCB component library, then do SCH component library. Requirements of PCB component library are higher,which directly affects the board installation.SCH component library requires relatively loose.As long as the attention to pin attributes and corresponding relationship with the PCB components. PS: Note hidden pins in the standard library. After that it is the schematic design.After finishing the schematic design,it is ready to do PCB design.

Second: PCB design. This step draws PCB board in the PCB design environment according to determined board size and the mechanical positioning,and according to the positioning requirements put the connector, button or switch, screw holes, mounting holes and so on. And fully consider and determine the wiring area and the non-wiring area .For example, how much area around the screw holes belongs to the non-wiring area?

Third: PCB layout. Layout means to put the device on the board. Then if the preparations mentioned above are ready, then you can generate a netlist (Design-> Create Netlist) on the schematic, and then import the netlist (Design-> Load Nets) on the PCB drawing.The components are all put up.There are fly line prompt connection among the pins.Then you can make layout for the device.

The following principles of the general layout :
①. According to the electrical performance,do the reasonable zoning,which generally can be divided into: digital circuit area where is fear of interference, and also makes interference, analog circuit area where is fear of interference,power driver region where is interference source;
②. When performing the same function circuit,they should be placed as close as possible, and we should adjust various components to ensure the connection is the most simple; At the same time, adjust the relative position of each block to make sure the connection among the function block is the most simple;
③. For large mass components, the installation location and mounting strength should be considered. The heating elements should be placed separately from the temperature-sensitive components.When necessary, thermal convection measures should be considered.
④. I / O driver device should be as close to the edge of the printing plate as possible,and near the lead connector;
⑤. A clock generator (eg: Crystal or Restructure) tries to close the device which may use this clock ;
⑥. Between power input pin and ground in each IC, you need to add a decoupling capacitor (generally monolithic capacitors with good high-frequency performance are used.) when board space is more dense, you can also add tantalum capacitors around a few integrated circuits.
⑦.The place of relay coil should be added the discharge diode (1N4148 is OK).
⑧. Layout requirements should be balanced and orderly. The layout can not be biased towards one end.

– Pay special attention:when placing components,the actual size (occupied area and height) of components and the relative position between the components must be considerred,in order to ensure the electrical performance of the circuit board and the feasibility and convenience of production and installation. At the same time,on the premise of guarantee to reflect the above principles ,appropriate modification of device placement makes it neat and beautiful.For example, the same device should be placed neatly in the same direction,and can not be put too “patchwork.” This step is related to the overall image of the board and the degree of difficulty in the next wiring.So it takes great effort to consider.When making the layout,you can make the preliminary wiring for the place where you are not sure.And you should have full consideration.

Fourth: cabling. Cabling is the most important step in entire PCB design.This will directly affect the performance of PCB is good or bad .In the PCB design process, the wiring is generally divided three realms: first,the wiring is smooth,which is the basic requirement of PCB design. If the line is not smooth, and everywhere is the fly line,that would be defective board. Followed by the meet of the electrical performance,which is a standard that can be used to measure the board is qualified or not.After the wiring is smooth, carefully adjust the wiring so that it can achieve the best electrical performance. Next it is beautiful.If your wiring is smooth,and there is no place which can effect electrical properties,but all is in a mess,even if electrical performance is good, in others’ eyes,it is just a piece of garbage,which cause great inconvenience for the test and maintenance.Wiring should be uniform,not maintenance.These can be achieved under the condition than can ensure the electrical properties and meet other individual requirements, or you concentrate on the trifles and neglect the essentials.

When wiring mainly according to the following principles:
①. Under normal circumstances,firstly do the wiring of power and ground wiring to ensure the electrical performance of the circuit board.Within the range of allowing conditions ,try to widen the power and ground line.It is better that ground line is wider than power line.Their width relationship is :Ground lines > power lines > signal lines. Generally signal line width is 0.2 ~ 0.3mm , the smallest width is up to 0.05 ~ 0.07mm,and the power lines is usually 1.2 ~ 2.5mm.For the PCB of digital circuit, you can use wide ground wire to form a loop,and that become a ground network to use(analog circuits can not be usde like this)
②.Do the wiring in advance for lines with the more stringent requirements,such as high frequency line.The edges of input and output terminal should avoid adjacent parallel,in order to avoide reflection interference.If necessary, add ground line to isolation.The wiring in two adjacent layers should be vertical.If they are paralles, it is to cause parasitic coupling.
③. Chassis of oscillator is on ground.The clock line should be as short as possible,and can not be attracted everywhere.
④. Do the wiring with 45° polyline as far as possible.Do not use 90° polyline,which reduce radiation of high frequency signal
⑤. Any signal lines do not form a loop.If it is inevitable, the loop should be as small as possible; via of signal lines should be as little as possible;
⑥. The key line should be short and thick, and is surrounded with protective ground.
⑦. When transmitting sensitive signal and the noise field signal through the flat cable, use the way of “Ground – Signal – ground” to leads.
⑧. Test points should be set aside for the key signal, to be convenient for the production and maintenance .
⑨. After completion of schematics wiring, wiring should be optimized.

– PCB wiring process requirement

①Line
In general, width of the signal line is 0.3mm (12mil), and the power line width is 0.77mm (30mil) or 1.27mm (50mil); the distance between lines and the distance between the lines and the pad are not less than 0.33mm (13mil ).In the actual application, if conditions permit, increasing the distance should be considered.When wiring density is higher,using two lines between IC feet can be considered,but not recommended.Line width is 0.254mm(10mil),and line spacing is not less than 0.254mm (10mil). In special cases, when the device pin is dense, the line width and line spacing can be appropriately reduced.

②. Pad (PAD)
The basic requirements of PAD and VIA are: diameter of PAD is larger 0.6mm than the hole . For example,for universal pin-type resistors, capacitors and integrated circuits,if the diameter of PAD is 1.6mm(32mil) and the diameter of holes is 0.8mm(32mil),the size of sockets, pins and diode 1N4007, etc should be 1.8mm （71mil）or 1.0mm（39mil）.In practical application, the size of PAD should be based on the actual size of the element.Conditionally, it may be appropriate to increase the size of the pad;The diameter of element mounting holes in PCB should be larger 0.2 ~ 0.4mm than the actual size of the element tin.

③. Vias (VIA)
Typically it is 1.27mm (50mil ) or 0.7mm ( 28mil);
When witing density is high,the via size can be ruduced appropriately,but not too small.You can consider 1.0mm(40mil) or 0.6mm ( 24mil)

(4)Spacing requirements of pad, line, and hole
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 rack their brains to design,after you finish the painting, and take a look, still feel a lot of places that you can modify. General design experience are: the time of wiring optimization is twice than the initial wiring time.If I feel no need to modify the place,you can shop the copper (Place-> polygon Plane).The shopped copper is generally ground wire(note that the analog ground shoulde separated from the digital ground).If multilayers. power may also be paved. For the silk screen,it can not be blocked by the device or removed by vias and pads . Meanwhile,when design,you should face the component layer,and the bottom layer should be mirrored, in order to avoid confusion level.

Sixth: The network and the DRC and structural inspection. First, under the circumstance of the right circuit schematic design,do the physical connection relationship check for the generated PCB network files and schematics network file.And timely correct the design according to the output file results, to ensure that the wiring connection relationship is right.After the network is checked and passed,check the pcb design by DRC.And timely correct the design according to the output file results, to ensure electrical performance.Finally, check and confirm the pcb mechanical mounting strcutre.

Seventh: making the board. Before that, it is better to have a review process.

PCB design is the work of a mind .People, whose mind is dense and experience is rich, design the board that is indeed good.So be extremely careful when design, and fully consider all aspects of the factors (for example, ease of maintenance and inspection that a lot of people do not consider).Be excelsior , we will be able to design a good board.

When talking about electrolytic capacitor, we shall know more about its role.

1, the filtering effect: in the power circuit, a rectifying circuit makes alternating current into the pulsating direct current.After a rectifier circuit ,access electrolytic capacitor of larger capacity.Using the properties of charge and discharge makes pulsating direct current voltage become relatively stable direct current voltage.

In practice, in order to prevent supply voltage of various parts of pcb manufacturing from change because of the change of electronic load, so the output of the power and the input of the power of the load generally have electrolytic capacitors of tens to hundreds of microfarads. Because large-capacity electrolytic capacitors generally have a certain inductance, which can not effectively filter out high frequency and pulse interference signal,so it has a capacitor with a capacity of 0.001–0.1 pF in parallel at both ends to filter out high frequency and pulse interference.

2, coupling effect: in transmission and amplification process of the low-frequency signal ,to prevent quiescent point of the front and back two level circuit from interaction effect,we often use the
capacitive coupling.To prevent too large loss of the low frequency component of the signal in the signal ,we usually use electrolytic capacitors with larger capacity.

Then we have to look at the judging method of electrolytic capacitors

Common faults of Electrolytic capacitor are : capacity reduce; the capacity disappear; breakdown ,short circuit and leakage.capacity change is caused by the gradual drying of the its inner electrolyte solution during the its use or place.While breakdown and leakage are caused by too high voltage that is added ro by itself poor quality.

Analyzing quality of the power capacitors of PCB prototype,we generally use the resistance of a multimeter to measure. Specific methods are: make two pins of capacitors short circuit ,to discharge,and then connect the positive of electrolytic capacitor with black pen of a multimeter ,connect the negative with red pen,which is for the pointer multimeter.If for digital multimeter,when measuring,the pens should have intermodulation. Normally hands should firstly swing in the direction of small resistance,then gradually return until infinity.If amplitude of swing of the hands is larger,or the return rate is slower,it indicates that the capacity of capacitor is greater.Otherwise, it indicates the capacity of capacitor is smaller.If the hand means no change somewhere in the middle,it indicates that this capacitor is leakage.If the resistance indicator value is very small or zero,it indicates that this capacitor is short-circuit breakdown.

Voltage of Battery that multimeter uses is generally low,so it is more accurate when measuring low-voltage capacitors, and when measuring high-voltage capacitor,although the measurement is normal,but when coupled with high pressure,it may appear leakage or breakway.

More attention to understanding the use of electrolytic capacitors

1, electrolytic capacitor has polarity, so the circuit can not be reversed . In the power supply circuit, when the output voltage is positive,then the positive of electrolytic capacitors connect the output of power,and the negative connect the ground.when the output voltage is negative,then the positive connect the output ,and the negative connect the ground.

When filter capacitor polarity of the power supply circuit reverse,because the filtering effect of the capacitor greatly reduce,which on the one hand cause fluctuation of power output voltage. On the other hand ,the reverse current makes electrolytic capacitors which is equivalent to resistance heat. When the reverse voltage exceeds a certain value, the reverse leakage resistance of capacitance will become very small,after power,it works soon,which can make the capacitor overheat, and then burst and damage.

2, voltage applied to both ends of the electrolytic capacitor can not exceed its allowable operating voltage. In the actual circuit design , a margin should leave depending on the circumstances.In the design of filter capacitor of stabilized voltage supply,if the voltage of AC power is 220v,secondary rectifier voltage of transformer can be up to 22v.When pcb prototype,using electrolytic capacitors of 25v can generally meet the requirements.

However, if fluctuations of the AC power supply voltage are large and likely to rise to more than 250V, it is better to use the electrolytic capacitor of 30V or more.

3, electrolytic capacitors in the circuit should not be close to the heating element with high power, to prevent electrolyte solution from accelerated drying because of the heat.

4, for the positive and negative polarity signal filtering ,we can use the method that two electrolytic capacitors connect in series with the same polarity,which can be treated as non-polar capacitor.

5, capacitor case, the auxiliary leads terminal, the positive and negative ,and the pcb board must be completely isolated.