What are the common errors in PCB? from szcaravan's blog

When studying or working on a PCB circuit board , you will encounter all kinds of big and small problems. In order to let everyone better solve these problems and avoid detours, today I will sort out some of the various problems encountered in PVBA

table of Contents:

1. Common Schematic Errors

2. Common errors in PCB

3. Common mistakes in PCB 

1. Common errors in schematic diagrams

(1) There is no signal connected to the ERC report pin:

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

     b. Inconsistent grid attributes are modified when components are created or placed, and the pins and wires are not connected;

     c. When creating the component, the pin direction is reversed, and the non-pin name end must be connected.

     d. The most common reason is that there is no project file, which is the most common mistake for beginners. Freewing  

(2) The component went out of the drawing boundary: no component was created in the center of the diagram paper of the component library.

(3) The network table of the created project file can only be partially transferred into the PCB circuit board: when generating the netlist, it is not selected as global.

(4) When using multi-part components created by yourself, never use annotate.

2. common errors in PCB

(1) It is reported that NODE is not found when the network is loaded

a. The components in the schematic diagram use packages that are not in the PCB circuit board library;

b. The components in the schematic diagram use packages with inconsistent names in the PCB library;

c. The components in the schematic diagram use packages with inconsistent pin numbers in the PCB library. For example, a triode: the pin numbers in sch are e, b, and c, while those in PCB are 1, 2, and 3.

(2) Can not always print on LX RC Jet one page when printing

a. It is not at the origin when creating the PCB library;

 b. The components have been moved and rotated many times, and there are hidden characters outside the boundaries of the PCB board. Choose to show all hidden characters, shrink the PCB, and then move the characters to the boundary.

(3) The DRC reporting network is divided into several parts:

This indicates that this network is not connected. Look at the report file and use the CONNECTED COPPER to find it.

If you make a more complicated design, try not to use automatic wiring.

3.common mistakes in the PCB manufacturing process

(1) Pad overlap

a. Causes heavy holes and breaks the drill, and damages the holes due to multiple drilling in one place during drilling.

b. In the multilayer board, there is both a connecting plate and an isolating plate at the same position, and the board is shown as • Isolation and connection errors.

(2) Irregular use of graphics layer

a. Violation of conventional design, such as the component surface design in the Bottom layer, and the welding surface design in the TOP layer, causing misunderstandings.

b. There is a lot of design rubbish on each layer, such as broken lines, useless borders, labels, etc.

(3) Unreasonable characters

a. The characters cover the SMD solder tabs, which brings inconvenience to the on-off detection of the PCB circuit board and component soldering.

b. The characters are too small, which makes screen printing difficult. If the characters are too large, they will overlap each other and be difficult to distinguish. The font is generally >40mil.

(4) Single-sided pad setting aperture

a. Single-sided pads are generally not drilled, and the aperture should be designed to be zero; otherwise, when the drilling data is generated, the coordinates of the hole will appear at this position. Special instructions should be given for drilling.

b. If a single-sided pad needs to be drilled, but the aperture is not designed, the software treats this pad as an SMT pad when outputting electrical and ground data, and the inner layer will lose the isolation disk.

(5) Draw pads with filling blocks

Although it can pass the DRC inspection, the solder mask data cannot be directly generated during processing, and the pad is covered with a solder mask and cannot be soldered.

(6) The electrical ground layer is designed with both a heat sink and a signal line, and the positive and negative images are designed together, and errors occur.

(7) Large area grid spacing is too small

Gridline spacing is less than 0.3mm. In the process of PCB manufacturing, the pattern transfer process will cause film breakage after development, which will increase the processing difficulty.

(8) The graphics are too close to the frame

At least 0.2mm or more spacing should be ensured (V-cut 0.35mm or more). Otherwise, the copper foil will be warped. The solder resist will fall off during the exterior processing, affecting the appearance quality (including the inner copper skin of the multilayer board).

(9) The outline frame design is not clear

In PCB manufacturing, many layers are designed with borders and do not overlap, which makes it difficult for PCB circuit board manufacturers to determine which line to form. The standard border should be designed on the mechanical layer or the 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 coating, and even causes warpage.

(11) Short shaped hole

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

(12) Milling profile positioning hole is not designed

If possible, design at least two positioning holes with a diameter> 1.5mm in the PCB circuit board.

(13) The aperture is not clearly marked

a. The aperture marking should be marked in the metric system as far as possible and in increments of 0.05.

b. Combine the apertures that may be combined into a reservoir area as much as possible.

c. Whether the tolerances of metalized holes and special holes (such as crimp holes) are clearly marked.

(14) Unreasonable wiring in the inner layer of the multilayer board

a. The heat dissipation pad is placed on the isolation tape, and it is easy to fail to connect after drilling.

b. There are gaps in the design of the isolation belt, which is easy to misunderstand.

c. The isolation band design is too narrow to accurately judge the network

(15) Design problem of buried blind hole plate

The significance of designing buried and blind vias:

a. Increase the density of the multilayer board by more than 30%, reduce the number of layers, and reduce the size of the multilayer board

b. Improve the performance of PCB circuit board, especially the control of characteristic impedance (shortened wire and reduced aperture)

c. Improve PCB design freedom

d. Reduce raw materials and costs, which is conducive to environmental protection.