Detailed PCB Screen Printing Bit Number of The Conventional Recommended Size, Adjustment Principles And Methods

Adjustment of screen printing bit number

For the later component assembly, especially manual assembly components, generally come up with PCB assembly diagrams, used for component placement and positioning, then the silkscreen bit number shows its necessity.

The silkscreen bit number on the PCB can be shown or hidden during production, but it does not affect the output of the assembly drawing. Press the shortcut key "L", press the button to close all layers, that is, close all layers, and then check the box to open only the silkscreen layer and the corresponding soldermask layer, you can adjust the silkscreen.

Principle of screen printing bit number adjustment and conventional recommended size

The following are the principles followed for screen printing bit number adjustment and the general recommended sizes:

(1) Silk-screen bit numbers are not on the soldermask and are missing after placement of the silk-screen production.

(2) Silk-screen bit numbers are clear, and the font size recommended word width/height dimensions are 4/25mil, 5/30mil, and 6/45mil.

(3) Keep the direction uniformity, generally a PCB should not be placed in more than two directions, recommended letters on the left or down, as shown in Figure 11-21.

Figure 11-21 Screen Printing Bit Number Display Direction

(4) For some silkscreen markings under the pendulum, they can be marked with placing 2D auxiliary lines or placing squares for easy reading, as shown in Figure 11-22.

Figure 11-22 Auxiliary lines and squares

Adjustment method of screen printing bit number

AltiumDesigner provides a quick way to adjust the silkscreen, the "Component Text Position" function, which allows you to quickly place the silkscreen around the component or in the center of the component.

(1) Select the component to be operated.

(2) Press the shortcut key "AP" to enter the "Component Text Position" dialog box, shown in Figure 11-23, the dialog box provides "Identifier" and "Note" two types of placement. The dialog box provides "Identifier" and "Note" two ways to place, here to "Identifier" as an example to explain.

(3) The "Identifier" provides upward, downward, rightward, leftward, upper-left, lower-left, upper-right, and lower-right directions, which correspond to the numeric keys on the keypad. By setting a shortcut key for the "Component Text Position" command, if you want to quickly place the silkscreen bit number of the selected component on top of the component, you can press the numeric keys "5" and "2" on the keypad to complete the operation. " will be able to complete this operation, as shown in Figure 11-24. Other direction placement is similar. For example, press the numeric keys "5" and "6" to place to the right side of the component, and press the numeric keys "5" and "8" to are placed below the component.

Figure 11-23 "Component Text Location" dialog box

Figure 11-24 Silk-screened bit numbers quickly placed on top of components

Some tips for PCB design

1、How to choose PCB board?

The selection of PCBs must strike a balance between meeting design requirements and mass production and cost. Design requirements include both electrical and mechanical components. This material issue is usually more important when designing very high speed PCBs (>GHz). For example, the FR-4 material commonly used nowadays may not be suitable as the dielectricloss at several GHz will have a significant impact on the signal attenuation. In terms of electrical, it is important to note that the dielectric constant (dielectricconstant) and dielectric loss at the designed frequency is suitable.

2. How to avoid high frequency interference?

The basic idea of avoiding high-frequency interference is to minimize the interference of electromagnetic fields of high-frequency signals, also known as crosstalk. The distance between the high-speed signal and the analog signal can be increased, or add groundguard/shunttraces next to the analog signal. Also pay attention to the digital ground to analog ground noise interference.

3、How to solve the problem of signal integrity in high-speed PCB design?

Signal integrity is basically a matter of impedance matching. The factors affecting impedance matching include the architecture and output impedance of the signal source, the characteristic impedance of the alignment, the characteristics of the load, and the topology of the alignment. The solution is to rely on the termination and adjustment of the topology of the alignment.

4、Can I add a ground wire in the middle of the differential signal line?

Differential signals in the middle of the general can not be added to the ground. Because the application principle of differential signals is the most important point is the use of differential signals coupled with each other (coupling) brought about by the benefits, such as fluxcancellation, anti-noise (noiseimmunity) ability. If you add a ground line in the middle, it will destroy the coupling effect.

5. Is it necessary to add ground shielding on both sides when laying out the clock?

Whether or not to add shielded ground depends on the crosstalk/EMI situation on the board, and it is possible to make the situation worse if the shielded ground is not handled properly.

6, allegro wiring appears a cut line segment (there is a small box) how to deal with?

The reason for this is that the module reuse automatically generates an auto-named group, so the key to solving this problem is to re-break up the group, by selecting the group in the placementedit state and then breaking it up.

Once you have completed this command, move all the small frames of the alignment to tap the ix00 coordinates.

7、How to meet the EMC requirements as far as possible, without causing too much cost pressure?

The increased cost of EMC on PCB boards is usually due to the increase in the number of ground layers to enhance the shielding effect and the addition of ferritebead, choke, and other high-frequency harmonic suppression devices. In addition, it is usually necessary to match the shielding structure of other organizations in order to make the whole system pass the EMC requirements. The following PCB board design techniques to provide a few to reduce the electromagnetic radiation generated by the circuit:

(1) As far as possible, use devices with slower signal slopes (slewrate) to reduce the high-frequency components produced by the signal.

(2) Pay attention to the location of the high-frequency device placement, not too close to the external connector.

(3) Pay attention to the impedance matching of high-speed signals, the alignment layer and its return current path (returncurrentpath) to reduce the reflection and radiation of high frequencies.

(4) In the power supply pins of each device to place enough and appropriate decoupling capacitors to moderate the power supply layer and the ground layer on the noise. Pay special attention to the frequency response and temperature characteristics of the capacitors to meet the design requirements.

(5) The ground in the vicinity of the external connector may be appropriately divided from the ground level, and the ground of the connector may be connected to the chassisground in close proximity.

(6) Appropriate use of groundguard/shunttraces in some special high-speed signal side. But pay attention to the guard/shunttraces on the impact of the characteristic impedance of the alignment.

(7) The power layer is 20 H more inwardly contracted than the ground layer, H being the distance between the power layer and the ground layer.

8, 2G or more high-frequency PCB design, microstrip design should follow which rules?

For RF microstrip line design, a 3D field analysis tool is required to extract the transmission line parameters. All the rules should be specified in this field extraction tool.

9, PCB board on the high-speed signal on the AC coupling near which end of the better results?

It is common to see different treatments, one close to the receiving end and one close to the transmitting end.

We first look at the role of the AC coupling capacitor, nothing more than three points: ① source and sink end of the DC is different, so isolate the DC; ② signal transmission may be crosstalk into the DC component, so isolate the DC signal to make a better eye diagram; ③ AC coupling capacitor can also provide DC bias and overcurrent protection. In the end, the role of the AC coupling capacitor is to provide DC bias, filter out the DC component of the signal, so that the signal is symmetrical about the 0 axis.

So why add this AC coupling capacitance? Of course there is a benefit, adding AC coupling capacitance certainly makes for better communication between the two stages and can improve the noise tolerance. It is important to realize that AC coupling capacitance is generally a point of discontinuity in the impedance of high-speed signals and can cause signal edges to become slow.

(1) Some protocols or manuals will provide design requirements that we place according to designguideline requirements.

(2) There is no requirement for the first one, so if it is IC to IC, place it close to the receiving end.

(3) If it is IC to connector, place it close to the connector.

10, PCB in the factory how to check whether the design process requirements?

Many PCB manufacturers go through a network on-off test with a power-up to ensure that all the linkages are correct before the PCB processing is completed and shipped out of the factory. At the same time, more and more manufacturers also use x-ray test to check some faults during etching or lamination. For finished boards after SMD processing, they are generally checked by ICT test, which requires adding ICT test points to the PCB design. If a problem occurs, a special x-ray inspection equipment can also be used to rule out whether the processing is the cause of the failure.