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Common mistakes in the PCB that professional has sorted out

105 Published by FASTPCBA 7月 11,2019

Common mistakes in the PCB that professional has sorted out

First, the schematic common mistakes

(1) The ERC report pin has no access signal:

A. I/O attributes are defined for the pins when the package is created;

B. The inconsistent grid attribute is modified when the component is created or placed, and the pin is not connected to the wire;

C. When the component is created, the pin direction is reversed and must be connected to the non-pin name.

D. The most common reason is that no project files have been created. This is the most common mistake for beginners.

(2)The component ran outside the drawing boundary: no component was created in the center of the component library chart paper.

(3) The created project file network table can only be partially transferred to pcb: when the netlist is generated, it is not selected as global.

(4) Never use annotate when using a multi-part component created by yourself.

pcb

Second, common errors in the PCB

(1) report that the NODE is not found when the network is loaded.

A. The components in the schematic use the package that is not in the pcb library;

B. The components in the schematic use the inconsistent package in the pcb library;

C. The components in the schematic use a package with inconsistent pin numbers in the pcb library. For example, the triode: sch pin number is e, b, c, and pcb is 1, 2, 3. Circuit board proofing to find FASTPCBA.

(2) Can’t always print to one page when printing

A. The pcb library is created at the originplace;

B. The component is moved and rotated multiple times, and there are hidden characters outside the pcb board. Select show all hidden characters, shrink pcb, and move characters to the border.

(3) The DRC Reporting Network is divided into several sections:

Indicates that the network is not connected. Look at the report file and use the option CONNECTED COPPER to find it.

If you are designing more complicated PCB, try not to use automatic layout.

pcb

Third, common mistakes in the PCB manufacturing process

(1)Pad overlap

A. Causes heavy holes, which cause breakage and hole damage during drilling due to multiple holes in one place.

B. In the multi-layer board, there are both lands and isolation discs in the same position, and the board is made to be isolated and connected incorrectly.

(2) The use of the graphics layer is not standardized

A. Violation of the conventional design, such as the design of the component surface in the Bottom layer, the welding surface design in the TOP layer, causing misunderstanding.

B. There are a lot of design garbage on each layer, such as broken lines, useless borders, labels, etc.

(3) The character is unreasonable.

A. The character covers the SMD soldering piece, which brings inconvenience to the PCB continuity detection and component soldering.

B. Characters are too small, making screen printing difficult, too large will make characters overlap each other, difficult to distinguish, the font is generally > 40mil.

(4) Single-sided pad setting aperture

A. Single-sided pad is generally not drilled, and its aperture should be designed to be zero. Otherwise, when drilling data is generated, the coordinates of the hole appear at this position. For example, the hole should be specially specified.

B. If the single-sided pad is to be drilled, but the aperture is not designed, the software will treat the pad as an SMT pad when outputting the ground and ground data, and the inner layer will drop the isolation disk.

(5) Draw pads with padding

Although this can be checked by DRC, the solder resist data cannot be directly generated during processing, and the pad is covered with the solder resist and cannot be soldered.

(6)The electric ground layer is designed with both a heat sink and a signal line, and the positive image and the negative image are designed together and an error occurs.

(7) Large area grid spacing is too small

Grid line spacing <0.3mm, during the PCB manufacturing process, the pattern transfer process produces a broken film after development to cause wire breakage. Improve processing difficulty.

(8) The graphic is too close to the outer frame

Should keep space at least 0.2mm or more (V-cut 0.35mm or more), otherwise the copper foil will be lifted and the solder resist will fall off during the external processing. It will affect the appearance quality (including the inner layer of copper in the multilayer board).

(9) The design of the outline frame is not clear

Many layers are designed with borders and do not overlap, which makes it difficult for PCB manufacturers to judge which line is to be formed. The standard frame should be designed on the mechanical layer or BOARD layer, and the internal hollowed out parts should be clear.

(10) Uneven graphic design

When the pattern is electroplated, the current distribution is uneven, which affects the uniformity of the plating layer and even causes warpage.

(11) Short shaped hole

The length/width of the shaped hole should be >2:1 and the width should be >1.0mm, otherwise the CNC drilling machine cannot be processed.

(12) Undesigned milling shape positioning hole

If possible, design at least 2 positioning holes with a diameter of >1.5mm in the PCB.

13) The aperture is not clearly marked

A. The aperture label should be marked as metric as much as possible and incremented by 0.05.

B. Combine the apertures that are likely to be merged into one pool area as much as possible.

C. Whether the tolerances of metallized holes and special holes (such as crimping holes) are clearly marked.

(14) The inner layer of the multilayer board is unreasonable

A. The heat sink pad is placed on the isolation tape, and it is easy to be unconnected after drilling.

B. The isolation belt is designed with a gap and is easy to misunderstand.

C. The isolation belt design is too narrow to accurately judge the network

(15) buried blind hole plate design problem. The significance of designing the buried blind hole plate:

A. increase the density of the multilayer plate by more than 30%, reduce the number of layers and reduce the number of layers Size

B. Improve PCB performance, especially control of characteristic impedance (wire shortening, aperture reduction)

C. Improve PCB design freedom

D. Reduce raw materials’costs, and contribute to environmental protection. Others have summarized these issues into work habits, and people with problems often have these bad habits.

Lack of planning

The common saying goes, “If a person has no plans beforehand, they will find that trouble will come to the door.” This of course also applies to the design of the PCB. One of the many steps to make a PCB design successfully is to choose the right tool. Today’s PCB design engineers find many powerful and easy-to-use EDA kits on the market. Each has its own unique capabilities, advantages and limitations. In addition, it should be noted that no software is foolproof, so problems such as component packaging mismatch will definitely occur. It’s possible that no single tool can satisfy all your needs. However, you must work hard to find the best product that best suits your needs. Some information on the web can help you get started quickly.

Poor communication

Poor communication Although the practice of outsourcing PCB design to other vendors is becoming more common and often very cost-effective, this approach may not be suitable for complex PCB designs. Performance and reliability are extremely critical in this design. As design complexity increases, to ensure accurate component placement and routing in real time, face-to-face communication between engineers and PCB designers becomes very important, and this face-to-face communication will help to save future expensive rework (rework).

Equally important, PCB board manufacturers should be invited to join in the early stages of the design process. The FASTPCBA is a supplier focused on 1-6 layers of proofing. You can check out the website https://www.automotivepcba.com/ to maximize efficiency according to its processes and procedures. In the long run, this will help you save considerable time and money. By letting them know your design goals and inviting them to participate in the early stages of PCB layout, you can avoid any potential problems and reduce time to market before the product is put into production.

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